Earth  

Famous "Blue Marble" photograph of Earth, taken from Apollo 17. The Blue Marble is a famous Photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft at
Orbital characteristics
Epoch J2000
Aphelion	152,097,701 km 1. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 0167103335 AU
Perihelion	147,098,074 km 0. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 9832898912 AU
Semi-major axis	149,597,887. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 5 km 1. 0000001124 AU
Eccentricity	0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 016710219
Orbital period	365. The orbital period is the time taken for a given object to make one complete Orbit about another object 256366 days 1. 0000175 yr
Average orbital speed	29. In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it 783 km/s 107,218 km/h
Inclination	Reference (0) 7. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 25° to Sun's equator
Longitude of ascending node	348. The Sun (Sol is the Star at the center of the Solar System. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 73936°
Argument of perihelion	114. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 20783°
Satellites	1 (the Moon)
Physical characteristics
Mean radius	6,371. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. 0 km[1]
Equatorial radius	6,378. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the 1 km[2]
Polar radius	6,356. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based 8 km[2]
Flattening	0. Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. 0033528[2]
Circumference	40,075. 02 km (equatorial) 40,007. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the 86 km (meridional) 40,041. The terms zonal and meridional are used to describe directions on a Globe. 47 km (mean)
Surface area	510,072,000 km²[3] 148,940,000 km² land  (29. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 2 %) 361,132,000 km² water (70. 8 %)
Volume	1. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 0832073×1012 km³
Mass	5. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 9736×1024 kg
Mean density	5. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 5153 g/cm³
Equatorial surface gravity	9.780327 m/s²[4] 0. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface 99732 g
Escape velocity	11. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 186 km/s  40,270 km/h
Sidereal rotation period	0. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars 997258 d 23h 56m 04. 09054s[4]
Equatorial rotation velocity	465. 11 m/s
Axial tilt	23. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 439281°
Albedo	0. The albedo of an object is the extent to which it diffusely reflects light from the sun 367
Surface temp.    Kelvin    Celsius	min mean max 184 K 287 K 331 K −89 °C 14 °C 57. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The Celsius Temperature scale was previously known as the centigrade scale. 7 °C
Adjectives	Terrestrial, Terran, Telluric, Tellurian, Earthly
Atmosphere
Surface pressure	101. Terra Mater or Tellus was a Goddess personifying the Earth in Roman mythology. 3 kPa (MSL)
Composition	78. Sea level can refer to Sea level, average height of the ocean Sea Level (band, 1970s musical group 08% Nitrogen (N2) 20. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 95% Oxygen (O2) 0. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 93% Argon 0. This article pertains to the chemical element For other uses see Argon (disambiguation. 038% Carbon dioxide About 1% water vapor (varies with climate)[5]

Earth (pronounced [ˈɝːθ] (help·info))^[6] is the third planet from the Sun. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is The Sun (Sol is the Star at the center of the Solar System. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different It is also referred to as the Earth, Planet Earth, the World, and Terra. "The world " is a proper noun for the planet Earth envisioned from an Anthropocentric or Human Worldview, as a place ^[7]

Home to millions of species,^[8] including humans, Earth is the only place in the universe where life is known to exist. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism Scientific evidence indicates that the planet formed 4.54 billion years ago,^{[9][10][11][12]} and life appeared on its surface within a billion years. Modern geologists and Geophysicists consider the age of Earth to be around 4 Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful radiation, permitting life on land. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In Biology, abiotic components are non-living Chemical and Physical factors in the environment. An aerobic organism or aerobe is an Organism that has an Oxygen based Metabolism. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges ^[13]

Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. In Geology, a crust is the outermost solid shell of a planet or moon Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and islands; liquid water, necessary for all known life, is not known to exist on any other planet's surface. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3 An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions An island (ˈaɪlənd or isle (/ˈaɪl/ is any piece of land that is completely surrounded by water in two dimensions above high tide and isolated from other significant Water is a common Chemical substance that is essential for the survival of all known forms of Life. ^[14][15] Earth's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided The inner core of the Earth, its innermost layer as detected by seismological studies, is a primarily solid Sphere about in radius only about 70%

Earth interacts with other objects in outer space, including the Sun and the Moon. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. At present, Earth orbits the Sun once for every roughly 366. 26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365. The sidereal year is the time taken for the Sun to return to the same position with respect to the Stars of the Celestial sphere. 26 solar days. Solar times are measures of the apparent position of the Sun on the Celestial sphere. ^[16] The Earth's axis of rotation is tilted 23. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 4° away from the perpendicular to its orbital plane,^[17] producing seasonal variations on the planet's surface with a period of one tropical year (365. In Geometry, two lines or planes (or a line and a plane are considered perpendicular (or orthogonal) to each other if they form congruent The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth 24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. 53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood A cometary bombardment during the early history of the planet played a role in the formation of the oceans. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — ^[18] Later, asteroid impacts caused significant changes to the surface environment. Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but

History

Main article: History of Earth

See also: Geological history of Earth

Scientists have been able to reconstruct detailed information about the planet's past. The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present geological history of Earth began 4567 billion years ago when the planets of the Solar System were formed out of the Solar nebula, a disk-shaped mass of Earth and the other planets in the Solar System formed 4. 54 billion years ago^[9] out of the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun. The formation and evolution of the Solar System is estimated to have begun Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. Melting is a process that results in the phase change of a substance from a Solid to a Liquid. The Moon formed soon afterwards, possibly as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass^[19] impacting the Earth in a glancing blow. ^[20] Some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.

Outgassing and volcanic activity produced the primordial atmosphere. Plate tectonics and hotspots Divergent plate boundaries At the Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated The question of the origin of water on Earth, or more accurately put the question of why there is clearly more Water on the Earth than on the other planets of the Solar ^[18] The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later, the last common ancestor of all life existed. The last universal ancestor ( LUA) also called the last universal common ancestor ( LUCA) the cenancestor or "number one" ^[21]

The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and resulted in a layer of ozone (a form of molecular oxygen [O₃]) in the upper atmosphere. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the OZONE is an object oriented Operating system written in the C programming language. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. The endosymbiotic theory concerns the origins of mitochondria and Plastids (e Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex ^[22] True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 ^[23]

Beginning with almost no dry land, the total amount of surface lying above the oceans has steadily increased. During the past two billion years, for example, the total size of the continents has doubled. ^[24] As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. In Geology, a supercontinent is a Landmass comprising more than one Continental core or Craton. Roughly 750 million years ago (mya), the earliest known supercontinent, Rodinia, began to break apart. In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". For the Genus of Metalmark butterflies, see Rodinia (butterfly. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which broke apart 180 mya. Pannotia, first described by Ian W D Dalziel in 1997 is a hypothetical Supercontinent that existed from the Pan-African orogeny about 600 million years ago to the Pangaea, Pangæa or Pangea (pænˈdʒiːə from παν pan, meaning entire, and Γαῖα Gaea, meaning Earth in ^[25]

Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 mya, during the Neoproterozoic, covered much of the planet in a sheet of ice. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. The Neoproterozoic Era is the unit of geologic time from 1000 to 542 +/- 0 This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate. The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the ^[26]

Following the Cambrian explosion, about 535 mya, there have been five mass extinctions. The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period ^[27] The last extinction event occurred 65 mya, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Over the past 65 million years, mammalian life has diversified, and several mya, an African ape-like animal gained the ability to stand upright. ^[28] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,^[29] affecting both the nature and quantity of other life forms.

The present pattern of ice ages began about 40 mya, then intensified during the Pleistocene about 3 mya. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago. ^[30]

Composition and structure

Main article: Earth science

Further information: Earth physical characteristics tables

Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet These are tables showing Composition and structure of Earth; Earth dimensions Continents and population See also A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily It is the largest of the four solar terrestrial planets, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity and the strongest magnetic field. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface ^[31]

Shape

Main article: Figure of the Earth

Size comparison of inner planets (left to right): Mercury, Venus, Earth, and Mars

The Earth's shape is very close to an oblate spheroid—a rounded shape with a bulge around the equator—although the precise shape (the geoid) varies from this by up to 100 meters. The expression figure of the Earth has various meanings in Geodesy according to the way it is used and the precision with which the Earth's size and shape is to be defined The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University An oblate Spheroid is a rotationally symmetric Ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The geoid is that Equipotential surface which would coincide exactly with the mean ocean surface of the Earth if the oceans were in equilibrium at rest and extended through ^[32] The average diameter of the reference spheroid is about 12,742 km. More approximately the distance is 40,000 km/π because the meter was originally defined as 1/10,000,000 of the distance from the equator to the north pole through Paris, France. IMPORTANT NOTICE Please note that Wikipedia is not a database to store the millions of digits of π please refrain from adding those to Wikipedia as it could cause technical problems The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern Paris (ˈpærɨs in English; in French) is the Capital of France and the country's largest city This article is about the country For a topic outline on this subject see List of basic France topics. ^[33]

The rotation of the Earth creates the equatorial bulge so that the equatorial diameter is 43 km larger than the pole to pole diameter. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation An equatorial bulge is a bulge which a planet may have around its Equator, distorting it into an Oblate spheroid. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based ^[34] The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Mount Everest, also called Sagarmatha (सगरमाथा meaning Head of the Sky) or Chomolungma, Qomolangma or Zhumulangma (in Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface The Mariana Trench (or Mariana's Trench) is the deepest part of the world's Oceans and the deepest location on the surface of the Earth 's Hence compared to a perfect ellipsoid, the Earth has a tolerance of about one part in about 584, or 0. An ellipsoid is a type of quadric surface that is a higher dimensional analogue of an Ellipse. Engineering tolerance is the permissible limit of variation in a physical Dimension, a measured value or Physical property of a 17%, which is less than the 0. 22% tolerance allowed in billiard balls. Billiard balls are used in Cue sports, such as Carom billiards, pool, and Snooker. ^[35] Because of the bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador. The inactive Stratovolcano Chimborazo (tʃimboˈraso is Ecuador's highest summit For a topic outline on this subject see List of basic Ecuador topics. ^[36]

Chemical composition

See also: Abundance of elements on Earth

The mass of the Earth is approximately 5. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 98×10²⁴ kg. It is composed mostly of iron (32. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 1%), oxygen (30. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 1%), silicon (15. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 1%), magnesium (13. Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 9%), sulfur (2. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 9%), nickel (1. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 8%), calcium (1. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 5%), and aluminium (1. WikipediaNaming 4%); with the remaining 1. 2% consisting of trace amounts of other elements. Due to mass segregation, the core region is believed to be primarily composed of iron (88. In Astronomy, dynamical mass segregation is the process by which heavier members of a gravitationally bound system such as a Star cluster or cluster of 8%), with smaller amounts of nickel (5. 8%), sulfur (4. 5%), and less than 1% trace elements. ^[37]

The geochemist F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. Frank Wigglesworth Clarke (1847-1931 was a chemist born in Boston Massachusetts 19 March, 1847. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. In Geology, a crust is the outermost solid shell of a planet or moon The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99. 22% were composed of 11 oxides (see the table at right. ) All the other constituents occur only in very small quantities. ^[38]

Internal structure

Main article: Structure of the Earth

Earth cutaway from core to exosphere. The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers Not to scale.

The interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers. A chemical substance is a Material with a definite chemical composition. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The silicate minerals make up the largest and most important class of rock-forming Minerals They are classified based on the structure of their silicate Ion group The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers The inner core of the Earth, its innermost layer as detected by seismological studies, is a primarily solid Sphere about in radius only about 70% The crust is separated from the mantle by the Mohorovičić discontinuity, and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. The Mohorovičić discontinuity, usually referred to as the Moho, is the boundary between the Earth 's crust and the mantle. ^[39]

The geologic component layers of the Earth^[40] are at the following depths below the surface:^[41]

The internal heat of the planet is probably produced by the radioactive decay of potassium-40, uranium-238 and thorium-232 isotopes. Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides All three have half-life decay periods of more than a billion years. Half-Life (computer-game page here It's already listed in the disambiguation page ^[42] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa. ^[43] A portion of the core's thermal energy is transported toward the crust by Mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. These plumes can produce hotspots and flood basalts. In Geology, a hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time A flood basalt or trap basalt is the result of a giant Volcanic eruption or series of Eruptions that coats large stretches of land or the Ocean floor ^[44]

Tectonic plates

Main article: Plate tectonics

A map illustrating the Earth's major plates. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere

According to plate tectonics theory, the outermost part of the Earth's interior is made up of two layers: the lithosphere, comprising the crust, and the solidified uppermost part of the mantle. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. In Geology, a crust is the outermost solid shell of a planet or moon The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Below the lithosphere lies the asthenosphere, which forms the inner part of the upper mantle. The asthenosphere (from an invented Greek a + ' sthenos "without strength" and Greek word σφαίρα (sphera meaning globe is the The asthenosphere behaves like a superheated material that is in a semi-fluidic, plastic-like state. ^[45]

The lithosphere essentially floats on the asthenosphere and is broken up into what are called tectonic plates. This is a list of tectonic plates on Earth Tectonic plates are pieces of the Earth's crust and uppermost mantle together referred to as the Lithosphere These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent, divergent and transform. In Plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region In Plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a A transform fault is a fault which runs along the boundary of a Tectonic plate. The last occurs where two plates move laterally relative to each other, creating a strike-slip fault. In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries. An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor ^[46]

The main plates are:^[47]

Notable minor plates include the Indian Plate, the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Pacific Ocean is the largest of the Earth 's Oceanic divisions The India or Indian Plate is a Tectonic plate that was originally a part of the ancient continent of Gondwanaland from which it split off eventually The Arabian Plate is one of three Tectonic plates (the African Arabian and Indian crustal plates) which have been moving northward over millions of The Caribbean Plate is a mostly oceanic Tectonic plate underlying Central America and the Caribbean Sea off the north coast of South The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic Tectonic plate in the eastern Pacific Ocean basin off the west South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a The Scotia Plate is an oceanic Tectonic plate bordering the South American Plate on the north the South Sandwich Plate to the east and the Antarctic The Australian Plate actually fused with Indian Plate between 50 and 55 million years ago. The India or Indian Plate is a Tectonic plate that was originally a part of the ancient continent of Gondwanaland from which it split off eventually The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/yr^[48] and the Pacific Plate moving 52–69 mm/yr. The Cocos Plate is an oceanic Tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides The Pacific Plate is an oceanic Tectonic plate beneath the Pacific Ocean. At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21 mm/yr. The Eurasian Plate is a Tectonic plate which includes most of the continent of Eurasia (a landmass consisting of the traditional Continents of Europe ^[49]

Surface

Main articles: Landform and Extreme points of the World

Present day Earth altimetry and bathymetry. This is a list of lists of extreme points of Earth, the points that are farther North, South, East or West than any other locations on the Terrain, or relief, is the third or vertical dimension of land surface. Bathymetry is the underwater equivalent to Hypsometry. The name comes from Greek βαθυς deep, and μετρον measure. Data from the National Geophysical Data Center's TerrainBase Digital Terrain Model. The National Geophysical Data Center (NGDC provides scientific stewardship products and services for Geophysical Data describing the solid Earth,

The Earth's terrain varies greatly from place to place. Terrain, or relief, is the third or vertical dimension of land surface. About 70. 8%^[50] of the surface is covered by water, with much of the continental shelf below sea level. The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes,^[34] oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by Plate tectonics and hotspots Divergent plate boundaries At the The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor A submarine canyon is a steep-sided Valley on the Sea floor of the Continental slope. An oceanic plateau (also submarine plateau) is an undersea Large igneous province, the equivalent of continental Flood basalts such as the Deccan Traps Abyssal plains are flat or very gently sloping areas of the deep Ocean basin floor The remaining 29. 2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies. A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak A desert is a Landscape or region that receives very little precipitation. In Geography, a plain is an area of land with relatively low relief — meaning that it is flat In Geology and Earth science, a plateau, also called a high plateau or tableland, is an area of highland, usually consisting Geomorphology (from Greek: γη ge, "earth" μορφή morfé, "form" and λόγος Logos, "knowledge"

The planetary surface undergoes reshaping over geological time periods due to the effects of tectonics and erosion. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts^[51] also act to reshape the landscape. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Coastal erosion is the wearing away of land or the removal of Beach or Dune Sediments by Wave action tidal currents, wave currents Coral reefs are Aragonite structures produced by living organisms found in marine waters with little to no nutrients in the water

As the continental plates migrate across the planet, the ocean floor is subducted under the leading edges. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other At the same time, upwellings of mantle material create a divergent boundary along mid-ocean ridges. In Plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by The combination of these processes continually recycles the ocean plate material. Most of the ocean floor is less than 100 million years in age. The oldest ocean plate is located in the Western Pacific, and has an estimated age of about 200 million years. By comparison, the oldest fossils found on land have an age of about 3 billion years. ^[52][53]

The continental plates consist of lower density material such as the igneous rocks granite and andesite. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. ^[54] Sedimentary rock is formed from the accumulation of sediment that becomes compacted together. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust. ^[55] The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change The most abundant silicate minerals on the Earth's surface include quartz, the feldspars, amphibole, mica, pyroxene and olivine. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg ^[56] Common carbonate minerals include calcite (found in limestone), aragonite and dolomite. Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3 Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed ^[57]

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. The pedosphere (from the Greek πέδον soil earth + σφαίρα sphere is the outermost layer of the Earth that is composed of Soil and subject to soil Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Pedogenesis or soil evolution (formation is the process by which Soil is created It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. A hydrosphere (from Greek ύδωρ - hydor, " Water " + σφαίρα - sphaira, " Sphere " The biosphere is the broadest level of ecological study the global sum of all Ecosystems. Currently the total arable land is 13. 31% of the land surface, with only 4. 71% supporting permanent crops. ^[58] Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1. 3×10⁷ km² of cropland and 3. 4×10⁷ km² of pastureland. ^[59]

Elevation histogram of the surface of the Earth—approximately 71% of the Earth's surface is covered with water. In Statistics, a histogram is a Graphical display of tabulated frequencies, shown as Bars It shows what proportion of cases fall into each of

The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The Dead Sea (יָם הַ‏‏מֶ‏ּ‏לַ‏ח, "Sea of Salt"البَحْر المَيّت, "Dead Sea" is a salt lake between Mount Everest, also called Sagarmatha (सगरमाथा meaning Head of the Sky) or Chomolungma, Qomolangma or Zhumulangma (in The mean height of land above sea level is 686 m. ^[60]

Hydrosphere

Main article: Hydrosphere

The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the solar system. A hydrosphere (from Greek ύδωρ - hydor, " Water " + σφαίρα - sphaira, " Sphere " The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of −10,911. The Challenger Deep is the deepest surveyed point in the oceans with a depth of about 11000 metres (about 36000 feet The Mariana Trench (or Mariana's Trench) is the deepest part of the world's Oceans and the deepest location on the surface of the Earth 's The Pacific Ocean is the largest of the Earth 's Oceanic divisions 4 m. ^[61][62] The average depth of the oceans is 3,794 m, more than five times the average height of the continents. ^[60]

The mass of the oceans is approximately 1. 35×10¹⁸ metric tons, or about 1/4400 of the total mass of the Earth, and occupies a volume of 1. This article is about the tonne or metric ton For other tons see Ton. 386×10⁹ km³. If all of the land on Earth were spread evenly, water would rise to an altitude of more than 2. 7 km. ^[63] About 97. 5% of the water is saline, while the remaining 2. 5% is fresh water. The majority of the fresh water, about 68. 7%, is currently in the form of ice. ^[64]

About 3. 5% of the total mass of the oceans consists of salt. Salt is a Dietary mineral composed primarily of Sodium chloride that is essential for Animal life but toxic to most land plants Most of this salt was released from volcanic activity or extracted from cool, igneous rocks. ^[65] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. ^[66] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. In Thermodynamics a heat reservoir is considered as a constant Temperature source ^[67] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation. El Niño-Southern Oscillation ( ENSO; commonly referred to as simply El Niño) is a global coupled ocean-atmosphere phenomenon ^[68]

Atmosphere

Main article: Earth's atmosphere

The atmospheric pressure on the surface of the Earth averages 101. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five 325 kPa, with a scale height of about 8. A scale height is a term often used in scientific contexts for a distance over which a quantity decreases by a factor of e. 5 km. ^[5] It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The height of the troposphere varies with latitude, ranging between 7 km at the poles to 17 km at the equator, with some variation due to weather factors. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the

Earth's biosphere has significantly altered its atmosphere. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Oxygenic photosynthesis evolved 2. Oxygen evolution is the process of generating molecular Oxygen through Chemical reaction. 7 billion years ago, forming the primarily nitrogen-oxygen atmosphere that exists today. The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks ultraviolet solar radiation, permitting life on land. An aerobic organism or aerobe is an Organism that has an Oxygen based Metabolism. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Other atmospheric functions important to life on Earth's include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. ^[69] This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. The Greenhouse effect refers to the change in the Thermal equilibrium temperature of a planet or moon by the presence of an Atmosphere containing gas that absorbs Carbon dioxide, water vapor, methane and ozone are the primary greenhouse gases in the Earth's atmosphere. Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared Without this heat-retention effect, the average surface temperature would be −18 °C and life would likely not exist. ^[50]

Weather and climate

Main articles: Weather and Climate

The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of Three-quarters of the atmosphere's mass is contained within the first 11 km of the planet's surface. This lowest layer is called the troposphere. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospheric circulation that drives the weather and climate through redistribution of heat energy. Atmospheric circulation is the large-scale movement of air and the means (together with the smaller Ocean circulation) by which Heat is distributed on the surface The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of ^[70]

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. The trade winds (also called trades) are the prevailing pattern of easterly winds found in the Tropics near the Earth's Equator. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The Westerlies or the Prevailing Westerlies are the prevailing winds in the Middle latitudes between 30 and 60 degrees Latitude, blowing from ^[71] Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes heat energy from the equatorial oceans to the polar regions. The term thermohaline circulation (THC refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and ^[72]

Source regions of global air masses. For airmass in Astronomy, see Airmass. In Meteorology, an air mass is a large volume of Air that

Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as precipitation. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric ^[70] Most of the water is then transported back to lower elevations by river systems, usually returning to the oceans or being deposited into lakes. "Riverine" redirects here For the use of that term in Maritime geography, see there A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the This water cycle is a vital mechanism for supporting life on land, and is a primary factor in the erosion of surface features over geological periods. The Earth 's Water is always in movement and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on above Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topological features and temperature differences determine the average precipitation that falls in each region. Atmospheric circulation is the large-scale movement of air and the means (together with the smaller Ocean circulation) by which Heat is distributed on the surface ^[73]

The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 The subtropics are the zones of the Earth immediately north and south of the tropic zone which is bounded by the Tropic of Cancer and the Tropic of Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. ^[74] Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. For airmass in Astronomy, see Airmass. In Meteorology, an air mass is a large volume of Air that The commonly-used Köppen climate classification system (as modified by Wladimir Köppen's student Rudolph Geiger) has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes. The Köppen climate classification is one of the most widely used climate classification systems It was developed by Wladimir Köppen, a German climatologist Wladimir Peter Köppen (Владимир Петрович Кёппен (born September 25, 1846 in Saint Petersburg, Russia &mdash died A desert is a Landscape or region that receives very little precipitation. Continental climate is a Climate that is characterized by Winter Temperatures cold enough to support a fixed period of Snow cover each Year ^[71]

Upper atmosphere

This view from orbit shows the full Moon partially obscured by the Earth's atmosphere. NASA image.

See also: Outer space

Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. This article is about the atmospheric mesosphere for the Earth's mantle see Mesosphere (mantle. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. ^[69] Each of these layers has a different lapse rate, defining the rate of change in temperature with height. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere Beyond these, the exosphere thins out into the magnetosphere (where the Earth's magnetic fields interact with the solar wind). The exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary at the edge of the Thermosphere is estimated to be 500 km to A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. ^[75] An important part of the atmosphere for life on Earth is the ozone layer, a component of the stratosphere that partially shields the surface from ultraviolet light. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 The Kármán line, defined as 100 km above the Earth's surface, is a working definition for the boundary between atmosphere and space. ^[76]

Due to thermal energy, some of the molecules at the outer edge of the Earth's atmosphere have their velocity increased to the point where they can escape from the planet's gravity. In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy This results in a slow but steady leakage of the atmosphere into space. There are several different processes that can lead to the escape of a planetary atmosphere. Because unfixed hydrogen has a low molecular weight, it can achieve escape velocity more readily and it leaks into outer space at a greater rate. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy ^[77] For this reason, the Earth's current environment is oxidizing, rather than reducing, with consequences for the chemical nature of life which developed on the planet. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state A chemical substance is a Material with a definite chemical composition. Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism The oxygen-rich atmosphere also preserves much of the surviving hydrogen by locking it up in water molecules. ^[78]

The Earth's magnetic field, which approximates a dipole. Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see

Magnetic field

Main article: Earth's magnetic field

The Earth's magnetic field is shaped roughly as a magnetic dipole, with the poles currently located proximate to the planet's geographic poles. Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a According to dynamo theory, the field is generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. The dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a Magnetic field. These in turn produce the Earth's magnetic field. The convection movements in the core are chaotic in nature, and periodically change alignment. This results in field reversals at irregular intervals averaging a few times every million years. A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged The most recent reversal occurred approximately 700,000 years ago. ^[79][80]

The field forms the magnetosphere, which deflects particles in the solar wind. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The sunward edge of the bow shock is located at about 13 times the radius of the Earth. A bow shock is a boundary between a Magnetosphere and an ambient medium The collision between the magnetic field and the solar wind forms the Van Allen radiation belts, a pair of concentric, torus-shaped regions of energetic charged particles. The Van Allen radiation belt is a Torus of energetic Charged particles ( plasma) around Earth, held in place by Earth's Magnetic In Geometry, a torus (pl tori) is a Surface of revolution generated by revolving a Circle in three dimensional space about an axis Coplanar In Physics, a charged particle is a particle with an Electric charge. When the plasma enters the Earth's atmosphere at the magnetic poles, it forms the aurora. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound ^[81]

Orbit and rotation

Main article: Earth's rotation

An animation showing the rotation of the Earth as seen from the northern hemisphere of the solar system. Rotation period Earth's rotation period relative to the Sun (its mean solar day is 86400 Seconds of mean solar time

Relative to the background stars, it takes the Earth, on average, 23 hours, 56 minutes and 4. 091 seconds (one sidereal day) to rotate around the axis that connects the north and the south poles from west to east. Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. ^[82] From Earth, the main apparent motion of celestial bodies in the sky (except that of meteors within the atmosphere and low-orbiting satellites) is to the west at a rate of 15°/h = 15'/min. This is equivalent to an apparent diameter of the Sun or Moon every two minutes. (The apparent sizes of the Sun and the Moon are approximately the same. )

Earth orbits the Sun at an average distance of about 150 million kilometers every 365. 2564 mean solar days (1 sidereal year). The sidereal year is the time taken for the Sun to return to the same position with respect to the Stars of the Celestial sphere. From Earth, this gives an apparent movement of the Sun with respect to the stars at a rate of about 1°/day (or a Sun or Moon diameter every 12 hours) eastward. Because of this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. Solar times are measures of the apparent position of the Sun on the Celestial sphere. This article is about the astronomical concept For other uses of the word see Meridian. The orbital speed of the Earth averages about 30 km/s (108,000 km/h), which is fast enough to cover the planet's diameter (about 12,600 km) in seven minutes, and the distance to the Moon (384,000 km) in four hours. ^[5]

Earth seen as a tiny dot by the Voyager 1 spacecraft, more than 6 billion kilometers from Earth. The Pale Blue Dot is a photograph of planet Earth taken by Voyager 1 from a record distance showing it against the vastness of space The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5,

The Moon revolves with the Earth around a common barycenter every 27. 32 days relative to the background stars. When combined with the Earth–Moon system's common revolution around the Sun, the period of the synodic month, from new moon to new moon, is 29. The month is a unit of Time, used with Calendars which is approximately as long as some natural period related to the motion of the Moon; 53 days. Viewed from the celestial north pole, the motion of Earth, the Moon and their axial rotations are all counter-clockwise. The north and south celestial poles are the two imaginary points in the sky where the Earth's Axis of rotation, "infinitely extended" intersects the A clockwise motion is one that proceeds 'like the Clock 's hands' from the top to the right then down and then to the left and back to the top The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 5 degrees from the perpendicular to the Earth–Sun plane (which causes the seasons); and the Earth–Moon plane is tilted about 5 degrees against the Earth-Sun plane (without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses). A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. A lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured ^[83][5]

Because of the axial tilt of the Earth, the position of the Sun in the sky (as seen by an observer on the surface) varies over the course of the year. For an observer at a northern latitude, when the northern pole is tilted toward the Sun the day lasts longer and the Sun climbs higher in the sky. This results in warmer average temperatures from the increase in solar radiation reaching the surface. When the northern pole is tilted away from the Sun, the reverse is true and the climate is generally cooler. Above the arctic circle, an extreme case is reached where there is no daylight at all for part of the year. The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. (This is called a polar night. The polar night is the night lasting more than 24 hours usually inside the Polar circles The opposite phenomenon when the sun stays above the horizon for a long time is called )

This variation in the climate (because of the direction of the Earth's axial tilt) results in the seasons. A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. By astronomical convention, the four seasons are determined by the solstices—the point in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when the direction of the tilt and the direction to the Sun are perpendicular. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Winter solstice occurs on about December 21, summer solstice is near June 21, spring equinox is around March 20 and autumnal equinox is about September 23. Events 69 - The end of the Year of the four emperors: Following Galba, Otho and Vitellius, Vespasian Events 524 - Godomar, King of the Burgundians defeats the Franks at the Battle of Vézeronce. Events 1600 - The Linköping Bloodbath takes place on Maundy Thursday in Linköping, Sweden. Events 1122 - Concordat of Worms. 1459 - Battle of Blore Heath, the first major battle of the English The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed.

The angle of the Earth's tilt is relatively stable over long periods of time. However, the tilt does undergo a slight, irregular motion (known as nutation) with a main period of 18. Nutation is a slight irregular motion (etymologically a "nodding" in the Axis of rotation of a largely axially symmetric object such as a Gyroscope 6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Precession refers to a change in the direction of the axis of a rotating object A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. An equatorial bulge is a bulge which a planet may have around its Equator, distorting it into an Oblate spheroid. From the perspective of the Earth, the poles also migrate a few meters across the surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. Polar motion is the movement of Earth 's rotation axis across its surface In Mathematics and Theoretical physics, quasiperiodic motion is in rough terms the type of motion executed by a Dynamical system containing a finite number In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. The Chandler wobble is a small motion in the Earth 's axis of rotation relative to the Earth's surface which was discovered by American Astronomer The rotational velocity of the Earth also varies in a phenomenon known as length of day variation. ^[84]

In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4 (for other eras, see precession and Milankovitch cycles). In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from Events 1431 - Joan of Arc is handed over to the Bishop Pierre Cauchon. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from Events 836 - Pactum Sicardi, peace between the Principality of Benevento and the Duchy of Naples In Astronomy, Precession refers to the movement of the rotational axis of a body such as a planet with respect to Inertial space. Milankovitch cycles are the collective effect of changes in the Earth 's movements upon its climate named after Serbian civil engineer and Mathematician The changing Earth-Sun distance results in an increase of about 6. 9%^[85] in solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere. ^[86]

The Hill sphere (gravitational sphere of influence) of the Earth is about 1. A Hill sphere is roughly the volume around an Astronomical body (such as a Planet) where it dominates in attraction of Satellites to that body rather Gravitation is a natural Phenomenon by which objects with Mass attract one another 5 Gm (or 1,500,000 kilometers) in radius. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand ^[87][88] This is maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.

Earth, along with the Solar System, is situated in the Milky Way galaxy, orbiting about 28,000 light years from the center of the galaxy, and about 20 light years above the galaxy's equatorial plane in the Orion spiral arm. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " The Orion Arm is a minor Spiral arm of the Milky Way galaxy The Solar System and Earth are within the Orion Arm ^[89]

Moon

Main article: Moon

The Moon is a relatively large, terrestrial, planet-like satellite, with a diameter about one-quarter of the Earth's. A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our It is the largest moon in the solar system relative to the size of its planet. (Charon is larger relative to the dwarf planet Pluto. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded ) The natural satellites orbiting other planets are called "moons" after Earth's Moon.

The gravitational attraction between the Earth and Moon causes tides on Earth. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the Earth. A separate article treats the phenomenon of Tidal resonance in Oceanography. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases: The dark part of the face is separated from the light part by the solar terminator. Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth The terminator is a fictive line that delimits the illuminated day side and dark Night side of a planetary body (also known as the "grey line" or

Because of their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm a year. Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs a year—add up to significant changes. To help compare Orders of magnitude of different Times this page lists times between 10&minus6 seconds and 10&minus5 seconds (1 micro ^[90] During the Devonian period, for example, (approximately 410 million years ago) there were 400 days in a year, with each day lasting 21. The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. 8 hours. ^[91]

The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon. Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. ^[92] Some theorists believe that without this stabilization against the torques applied by the Sun and planets to the Earth's equatorial bulge, the rotational axis might be chaotically unstable, as it appears to be for Mars. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about If Earth's axis of rotation were to approach the plane of the ecliptic, extremely severe weather could result from the resulting extreme seasonal differences. The ecliptic is the apparent path that the Sun traces out in the sky during the year One pole would be pointed directly toward the Sun during summer and directly away during winter. Planetary scientists who have studied the effect claim that this might kill all large animal and higher plant life. Planetary science, also known as planetology and closely related to planetary astronomy, is the Science of Planets or Planetary systems ^[93] However, this is a controversial subject, and further studies of Mars—which has a similar rotation period and axial tilt as Earth, but not its large Moon or liquid core—may settle the matter. Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane.

Viewed from Earth, the Moon is just far enough away to have very nearly the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle The solid angle, Ω, is the angle in three-dimensional space that an object Subtends at a point This allows total and annular eclipses to occur on Earth. An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another

A scale representation of the relative sizes of, and distance between, Earth and Moon.

The most widely accepted theory of the Moon's origin, the giant impact theory, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. Protoplanets are moon-sized planets or larger embryos within Protoplanetary discs They are believed to form out of kilometer-sized Planetesimals that attract each This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust. ^[94]

Earth has at least two co-orbital asteroids, 3753 Cruithne and 2002 AA₂₉. A quasi-satellite is an object in a 11 Orbital resonance with its Planet that stays close to the planet over many orbital periods TemplateInfobox Planet. --> 3753 Cruithne (ˈkrɪnjə from Old Irish ˈkrɪθnɛ Modern TemplateInfobox Planet. -->Asteroid ( also written 2002 AA29) is a Near-Earth asteroid ^[95]

Habitability

See also: Planetary habitability

A planet that can sustain life is termed habitable, even if life did not originate there. Planetary habitability is the measure of a Planet 's or a Natural satellite 's potential to develop and sustain Life. The Earth provides the (currently understood) requisite conditions of liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain metabolism. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. ^[96] The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the conditions necessary to originate and sustain life on this planet. ^[97]

Biosphere

Main article: Biosphere

The planet's life forms are sometimes said to form a "biosphere". The biosphere is the broadest level of ecological study the global sum of all Ecosystems. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. This biosphere is generally believed to have begun evolving about 3. eVolution is the third Album by eLDee, it was due to be released in 2008 5 billion years ago. Earth is the only place in the universe where life is known to exist. Some scientists believe that Earth-like biospheres might be rare. In Planetary astronomy and Astrobiology, the Rare Earth hypothesis argues that the emergence of complex Multicellular life ( Metazoa ^[98]

The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. A biome is a climatically and geographically defined area of ecologically similar climatic conditions such as communities of Plants Animals and Plants are living Organisms belonging to the kingdom Plantae. On land primarily latitude and height above the sea level separates biomes. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Terrestrial biomes lying within the Arctic, Antarctic Circle or in high altitudes are relatively barren of plant and animal life, while the greatest latitudinal diversity of species is found at the Equator. The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. The Antarctic Circle is one of the five major circles (or parallels of latitude that mark maps of the Earth. Plants are living Organisms belonging to the kingdom Plantae. The pattern The increase in species richness or Biodiversity that occurs from the Poles to the Tropics, often referred to as the latitudinal gradient The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the ^[99]

Natural resources and land use

Main article: Natural resource

The Earth provides resources that are exploitable by humans for useful purposes. Natural resources are naturally occurring substances that are considered valuable in their relatively unmodified ( natural) form Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale. Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust.

Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. Petroleum ( L petroleum, from Greek πετρέλαιον, lit Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Methane clathrate, also called methane hydrate or methane ice, is a solid form of water that contains a large amount of Methane within its Crystal These deposits are used by humans both for energy production and as feedstock for chemical production. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere ^[100] These bodies form concentrated sources for many metals and other useful elements. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus.

The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( Topsoil is the upper outermost layer of soil usually the top 2 to 8 inches An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( ^[101] Humans also live on the land by using building materials to construct shelters. The ecological footprint is a measure of human demand on the Earth's Ecosystems. For other kinds of building materials see Hardware, Biology, Star formation. A home is a place of Residence or Refuge. It is usually a place where an individual or a family can rest in and be able to store Personal property. In 1993, human use of land is approximately:

The estimated amount of irrigated land in 1993 was 2,481,250 km². ^[58]

Natural and environmental hazards

Large areas are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other calamities and disasters. An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur A tsunami ((tsuːˈnɑːmi is a series of waves created when Plate tectonics and hotspots Divergent plate boundaries At the A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or Cenote, is a natural depression A blizzard is a severe Winter storm condition characterized by low Temperatures strong Winds and heavy blowing Snow Blizzards are formed when A flood is an overflow of an expanse of water that submerges land a deluge A drought is an extended period of months or years when a region notes a deficiency in its water supply A disaster is the impact of a natural or human-made hazard that negatively affects society or environment.

Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species. Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in Acid rain is Rain or any other form of precipitation that is unusually Acidic It has harmful effects on plants aquatic animals and infastructure Overgrazing occurs when plants are exposed to Livestock Grazing for extended periods of time or without sufficient recovery periods Deforestation is the conversion of Forested areas to non-forest land for use such as Arable land, Pasture, urban use logged area or wasteland Desertification is the degradation of land in arid and dry sub-humid areas resulting primarily from human activities and influenced by climatic variations Wildlife includes all non-domesticated plants animals and other organisms In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Soils retrogression and degradation in the French school of pedology are two regressive evolution processes associated with the loss of equilibrium of a stable Soil Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Introduced species|Weed Invasive species is a phrase with several definitions

A scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. Scientific consensus is the collective judgement position and Opinion of the community of Scientists in a particular field of Science at a particular Global warming is the increase in the average measured temperature of the Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather conditions and a global rise in average sea levels. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. An ice sheet is a mass of Glacier Ice that covers surrounding terrain and is greater than 50000 km² (20000 mile²) Sea-level rise is an increase in Sea level. Multiple complex factors may influence this change ^[102]

Human geography

Main article: Human geography

See also: World

The Earth at night, a composite of DMSP/OLS ground illumination data on a simulated night-time image of the world. Human geography is a branch of Geography that focuses on the study of patterns and processes that shape human interaction with the environment with particular reference to "The world " is a proper noun for the planet Earth envisioned from an Anthropocentric or Human Worldview, as a place South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a The Pacific Ocean is the largest of the Earth 's Oceanic divisions The Pacific Ocean is the largest of the Earth 's Oceanic divisions The Indian Ocean is the third largest of the world's Oceanic divisions covering about 20% of the water on the Earth 's surface The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region is the smallest and shallowest of the world's five major The Middle East is a Subcontinent with no clear boundaries often used as a synonym to Near East, in opposition to Far East. The Caribbean (ˌkærəˡbiən kæ'rəbiən Cariben|Caraïben or Caraïben; Caraïbe or more commonly Antilles; Caribe is a Region consisting Central Asia is a region of Asia from the Caspian Sea in the west to central China in the east and from southern Russia in the north to northern Pakistan in the south North Asia or Northern Asia is sometimes defined as a Subregion of Asia consisting only of the Asian portion of Russia. Southwest Asia or Southwestern Asia (largely overlapping with the Middle East) is the southwestern portion of Asia. Australasia is a Region of Oceania: New Zealand, Australia, Papua New Guinea, and neighbouring Islands in the Pacific Melanesia (from Greek: μέλας black, νῆσος island) means "islands of the black-skinned people" Micronesia, from the Greek mikros (μικρός (meaning small) and nesos (νῆσος (meaning island) is a Subregion Polynesia (from Greek: πολύς many, νῆσος island) is a Subregion of Oceania, comprising a large grouping of over The Americas are the lands of the Western hemisphere or New World, consisting of the Continents of North America and South America Central Africa is a core Region of the African Continent often considered to include Burundi, the Central African Republic, Chad East Africa is the Easternmost Region of the African Continent. North Africa or Northern Africa is the Northernmost Region of the African Continent, separated by the Sahara from Sub-Saharan Southern Africa is the Southernmost Region of the African Continent, variably defined by Geography or Geopolitics. West Africa or Western Africa is the Westernmost Region of the African Continent. Central Europe is the Region lying between the variously and vaguely defined areas of Eastern and Eastern Europe is a general term that refers to the Geopolitical region encompassing the easternmost part of the European continent. Northern Europe is a term for the northern part of Europe. The United Nations defines Northern Europe as (Finland The term Southern Europe can have four definitions geographical political climatic phytogeographic Western Europe at its most general meaning means 'all the countries in the West of Europe ' The Defense Meteorological Satellite Program (DMSP monitors Meteorological, oceanographic and solar-terrestrial physics for the United States Department of Defense This image is not photographic and many features are brighter than they would appear to a direct observer. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing

Earth has approximately 6,671,226,000 human inhabitants as of July 2007. ^[103] Projections indicate that the world's human population will reach seven billion in 2013 and 9. The world population is the total number of living Humans on Earth at a given time 2 billion^[104] in 2050. Most of the growth is expected to take place in developing nations. Developing countries are countries that haven't reached Western-style standards of democratic government free market economy industrialization social programs and human rights guaranties Human population density varies widely around the world, but a majority live in Asia. Population density (in agriculture standing stock and Standing crop) is a measurement of Population per unit area or unit volume By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas. Rural areas can be large and isolated (also referred to as "the country" and/or "the countryside over the course of time ^[105]

It is estimated that only one eighth of the surface of the Earth is suitable for humans to live on—three-quarters is covered by oceans, and half of the land area is either desert (14%),^[106] high mountains (27%),^[107] or other less suitable terrain. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. A desert is a Landscape or region that receives very little precipitation. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada. Alert, in the Qikiqtaaluk Region, Nunavut Canada, is the northernmost permanently inhabited place in the world Ellesmere Island is part of the Qikiqtaaluk Region of the Canadian territory of Nunavut. Nunavut (ˈnuːnəvʊt ( Inuktitut syllabics: ᓄᓇᕗᑦ is the largest and newest territory of Canada; it was separated officially from the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page ^[108] (82°28′N) The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole. Description and history The Amundsen-Scott South Pole Station is the southernmost continually inhabited place on the planet The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. (90°S)

Independent sovereign nations claim all of the planet's land surface, with the exception of some parts of Antarctica. A nation is a Human Cultural and Social Community. In as much as most members never meet each other yet feel a common bond it may be considered As of 2007 there are 201 sovereign states, including the 192 United Nations member states. This list of sovereign states, alphabetically arranged gives an overview of States around the world with information on the extent of their Sovereignty. This article lists the member states of the United Nations (UN. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities. A dependent territory dependent area or dependency is a territory that does not possess full political Independence or Sovereignty as a ||-||}This list of Autonomous areas arranged by country gives an overview of autonomous areas of the world This is a list of extant Territorial disputes around the world Historically, Earth has never had a sovereign government with authority over the entire globe, although a number of nation-states have striven for world domination and failed. Sovereignty is the exclusive Right to control a Government, a country, a people or oneself For the government of parliamentary systems see Executive (government. World domination (sometimes world conquest, global domination, or Colloquially taking over the world) in which a single political authority

The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict. The United Nations ( UN) is an International organization whose stated aims are to facilitate cooperation in International law, International security International Organization is a peer-reviewed Academic journal that covers the entire field of International affairs. It is not, however, a world government. While the U. N. provides a mechanism for international law and, when the consensus of the membership permits, armed intervention,^[109] it serves primarily as a forum for international diplomacy. International law is the term commonly used for referring to the system of implicit and explicit agreements that bind together nation-states in adherence to recognized values and standards

In total, about 400 people have been outside the Earth's atmosphere as of 2004, and, of these, twelve have walked on the Moon. Normally the only humans in space are those on the International Space Station. The station's crew of three people is usually replaced every six months.

Cultural viewpoint

The first photograph ever taken of an "Earthrise," on Apollo 8.

Etymology

The name Earth originates from the 8th century Anglo-Saxon word erda, which means ground or soil. In Old English the word became eorthe, then erthe in Middle English. Middle English is the name given by Historical linguistics to the diverse forms of the English language spoken between the Norman invasion of ^[110] Earth was first used as the name of the sphere of the Earth around 1400. ^[111] It is the only planet whose name in English is not derived from Greco-Roman mythology. Greek mythology is the body of stories belonging to the ancient Greeks concerning their gods and Heroes the nature of the world and the origins and significance Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its

The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle. This symbol is known as the wheel cross, sun cross, Odin's cross or Woden's cross. Although it has been used in various cultures for different purposes, it came to represent the compass points, earth and the land. Another version of the symbol is a cross on top of a circle; a stylized globus cruciger that was also used as an early astronomical symbol for the planet Earth. The globus cruciger ( Latin, "cross-bearing orb" is an orb (lat ^[112]

Religious beliefs

Earth has often been personified as a deity, in particular a goddess. See also List of deities A deity is a Postulated Preternatural or Supernatural Being, who is always A goddess is a Female Deity. Many Cultures have goddesses Often deities are part of a polytheistic system that includes several deities In many cultures the mother goddess, also called the Mother Earth, is also portrayed as a fertility deity. A mother goddess is a Goddess, often portrayed as the Earth Mother who serves as a general Fertility deity the bountiful embodiment of the Earth. In polytheistic religions and mythologies a fertility god is a male deity who is responsible for ensuring human Fertility. See also Graha. Graha (from Sanskrit ग्रह gráha -- seizing laying hold of holding is a 'cosmic influencer' on the living beings of mother Bhumidevi ( Earth) To the Aztec, Earth was called Tonantzin—"our mother"; to the Incas, Earth was called Pachamama—"mother earth". Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political In Aztec mythology, Tonantzin is a considered Mother Earth Among the titles and honorifics bestowed upon Tonantzin are "Goddess of Sustenance" "Honored Pachamama is a goddess revered by the indigenous people of the Andes. The Chinese Earth goddess Hou-T'u^[113] is similar to Gaia, the Greek goddess personifying the Earth. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Gaia (ˈgeɪə or /ˈgaɪə/ (" land " or " Earth " from the Ancient Greek Γαîα also Gæa or Gea To Hindus it is called Bhuma Devi, the Goddess of Earth. A Hindu ( Devanagari: हिन्दू is an adherent of the philosophies and scriptures of Hinduism, a set of religious, Philosophical Bhūma Devī or Bhūmi-Devī or Bhū Devī is the divine wife of Lord Varaha, an Avatar of Lord Vishnu. In Norse mythology, the Earth goddess Jord was the mother of Thor and the daughter of Annar. Norse mythology comprises the indigenous pre-Christian religion, beliefs and Legends of the Scandinavian peoples including those who settled on Iceland In Norse mythology, Jörð ( Old Norse "earth" jɔrð Jarð jɑrð in Old East Norse --> sometimes Anglicized as Jord Thor ( Old Norse: Þórr) is the red-haired and bearded God of Thunder in Germanic paganism and its subset Norse paganism In Norse mythology, according to the Gylfaginning, Annar ( Old Norse Annarr 'second another' was the father of Jörd 'Earth' Ancient Egyptian mythology is different from that of other cultures because Earth is male, Geb, and sky is female, Nut. Ancient Egyptian religion encompasses the various religious beliefs and rituals practiced in Ancient Egypt from the predynastic period until the adoption of Christianity Geb (pronunciation as such from the Greek period onwards formerly erroneously read as Seb) or Keb (in Egyptian originally Gebeb/Kebeb meaning probably In the Ennead Mythology, Nut (alternatively spelled Nuit, Newet and Neuth was the goddess of the Sky.

In many religions, creation myths exist, recalling a story involving the creation of the Earth by a supernatural deity or deities. A religion is a set of Tenets and practices often centered upon specific Supernatural and moral claims about Reality, the Cosmos A creation myth is a supernatural mytho-[[religion religious]] story or explanation that describes the beginnings of humanity, Earth, life, and See also List of deities A deity is a Postulated Preternatural or Supernatural Being, who is always A variety of religious groups, often associated with fundamentalist branches of Protestantism,^[114] or Islam,^[115] assert that their interpretations of the accounts of creation in sacred texts are literal truth and should be considered alongside or replace conventional scientific accounts of the formation of the Earth, and the origin and development of life. Fundamentalism refers to a "deep and totalistic commitment" to a belief in and strict adherence to a set of basic principles (often Religious in nature a reaction Protestantism refers to the forms of Christian faith and practice that originated in the 16th century Protestant Reformation. For other meanings including people named 'Islam' see Islam (disambiguation. Hermeneutics may be described as the development and study of Theories of the interpretation and understanding of texts Creation science or scientific creationism is a movement within Creationism which attempts to use scientific means to disprove the accepted scientific theories on ^[116] Such assertions are opposed by both the scientific community,^[117][118] and other religious groups. The scientific community consists of the total body of Scientists its relationships and interactions ^{[119][120][121]} For a prominent example, see the creation-evolution controversy. The creation-evolution controversy (also termed the creation vs

Exploration and mapping

In the ancient past there were varying levels of belief in a flat Earth, with the Mesopotamian culture portraying the world as a flat disk afloat in an ocean. The idea of a flat Earth is the idea that the surface of the Earth is flat (a plane) rather than the view that it is a very close approximation of Mesopotamian mythology is the collective name given to Sumerian Akkadian Assyrian and Babylonian mythologies from the land between the Tigris The spherical form of the Earth was suggested by early Greek philosophers; a belief espoused by Pythagoras. Ancient Greek philosophy focused on the role of Reason and Inquiry. "Pythagoras of Samos" redirects here For the Samian statuary of the same name see Pythagoras (sculptor. By the Middle Ages—as evidenced by thinkers such as Thomas Aquinas—European belief in a spherical Earth was widespread. The concept of a spherical Earth dates back to around the 6th century BC in ancient Greek philosophy and possibly ancient Indian philosophy. ^[122] Prior to circumnavigation of the planet and the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets. Spaceflight is the use of Space technology to fly a Spacecraft into and through Outer space. ^[123]

Cartography, the study and practice of map making, and vicariously geography, have historically been the disciplines devoted to depicting the Earth. Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena Surveying, the determination of locations and distances, to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information. Surveying is the technique and science of accurately determining the terrestrial or three-dimensional space Position of points and the distances and angles between Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another

Modern perspective

See also: Spaceship Earth, Gaia theory, and Geocentric orbit

The technological developments of the latter half of the 20th century are widely considered to have altered the public's perception of the Earth. Spaceship is a World view term usually expressing concern over the use of limited resources available on Earth. The Gaia hypothesis is an ecological Hypothesis proposing that the Biosphere and the physical components of the Earth ( Atmosphere Before space flight, the popular image of Earth was of a green world. Science fiction artist Frank R. Paul provided perhaps the first image of a cloudless blue planet (with sharply defined land masses) on the back cover of the July 1940 issue of Amazing Stories, a common depiction for several decades thereafter. Frank Rudolph Paul ( April 18 1884 - June 29 1963) was an illustrator of US Pulp magazines in the Science fiction field Amazing Stories was an American Science fiction magazine launched in April 1926 by Hugo Gernsback 's Experimenter Publishing. ^[124]

Earth and Moon from Mars, imaged by Mars Global Surveyor. The Mars Global Surveyor ( MGS) was a US Spacecraft developed by NASA and the Jet Propulsion Laboratory and launched From space, the Earth can be seen to go through phases similar to the phases of the Moon. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth

Earth was first photographed from space by Explorer 6 in 1959. Explorer 6 (1959-004A or S-2) was a United States Satellite launched on August 7, 1959. ^[125] Yuri Gagarin became the first human to view Earth from space in 1961. The crew of the Apollo 8 was the first to view an Earth-rise from lunar orbit in 1968. In 1972 the crew of the Apollo 17 produced the famous "Blue Marble" photograph of the planet Earth from cislunar space (see top of page). The Blue Marble is a famous Photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft at Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. This became an iconic image of the planet as a marble of cloud-swirled blue ocean broken by green-brown continents. NASA archivist Mike Gentry has speculated that "The Blue Marble" is the most widely distributed image in human history. A photo taken of a distant Earth by Voyager 1 in 1990 inspired Carl Sagan to describe the planet as a "Pale Blue Dot. The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, Carl Edward Sagan ( November 9 1934 &ndash December 20 1996) was an American Astronomer, astrochemist, author The Pale Blue Dot is a photograph of planet Earth taken by Voyager 1 from a record distance showing it against the vastness of space "^[126] Earth has also been described as a massive spaceship, with a life support system that requires maintenance,^[127] or as having a biosphere that forms one large organism. A spacecraft is a Vehicle or machine designed for Spaceflight. In Human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space The biosphere is the broadest level of ecological study the global sum of all Ecosystems. ^[128]

Over the past two centuries a growing environmental movement has emerged that is concerned about humankind's effects on the Earth. The environmental movement, a term that includes the conservation and green movements is a diverse scientific social and Political movement for The key issues of this socio-political movement are the conservation of natural resources, elimination of pollution, and the usage of land. The conservation movement also known as nature conservation is a political social and to some extent scientific movement that seeks to protect natural resources including Natural resources are naturally occurring substances that are considered valuable in their relatively unmodified ( natural) form Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in Environmentalists advocate sustainable management of resources and stewardship of the environment through changes in public policy and individual behavior. Sustainability, in a general sense is the capacity to maintain a certain process or state indefinitely Stewardship is personal responsibility for taking care of another person's property or financial affairs or in religious orders taking care of finances See also Natural environment The '''biophysical''' environment is the symbiosis between the physical environment and the Biological Of particular concern is the large-scale exploitation of non-renewable resources. Changes sought by the environmental movements are sometimes in conflict with commercial interests due to the additional costs associated with managing the environmental impact of those interests. ^[129]

Future

See also: Risks to civilization, humans and planet Earth

The future of the planet is closely tied to that of the Sun. This is about the future of civilization humans and the earth As a result of the steady accumulation of helium ash at the Sun's core, the star's total luminosity will slowly increase. The solar luminosity, L_\odot is a unit of Luminosity ( power emitted in the form of Photons conventionally used by Astronomers to The luminosity of the Sun will increase by 10 percent over the next 1. 1 billion years (1. 1 Gyr), and by 40% over the next 3. In Astronomy, Geology, and Paleontology, bya or " bya " is an Acronym for billion years ago. 5 Gyr. ^[130] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans. ^[131]

The Earth's increasing surface temperature will accelerate the inorganic CO₂ cycle, reducing its concentration to the lethal levels for plants (10 ppm for C4 photosynthesis) in 900 million years. Traditionally inorganic compounds are considered to be of mineral not biological origin The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the Biosphere, Pedosphere, Geosphere, Hydrosphere, and "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly C4 carbon fixation is one of three biochemical mechanisms along with C3 and CAM photosynthesis, functioning in land Plants to The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years. ^[24] But even if the Sun were eternal and stable, the continued internal cooling of the Earth would have resulted in a loss of much of its atmosphere and oceans (due to lower volcanism). Plate tectonics and hotspots Divergent plate boundaries At the ^[132] After another billion years the surface water will have completely disappeared^[133] and the mean global temperature will reach 70°C. ^[24] The Earth is expected to be effectively habitable for another 500 million years or so. ^[134]

The Sun, as part of its evolution, will expand to a red giant in about 5 Gyr. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime A red giant is a luminous Giant star of low or intermediate mass (roughly 0 Models predict that the Sun will expand out to about 250 times its present size, roughly 1 AU (150,000,000 km). The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand ^[130][135] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will be in an orbit 1. 7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. Therefore, the planet is thought to escape envelopment by the expanded Sun's sparse outer atmosphere, though most (if not all) existing life would have been destroyed by the Sun's proximity to Earth. ^[130] However, a more recent simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be destroyed. ^[135]

See also

• List of Earth-related topics
• List of basic Earth science topics
• List of Earth science topics (alphabetical)
• List of basic geography topics
• List of basic geology topics

Notes

References

• Comins, Neil F. (2001). Discovering the Essential Universe, Second Edition, W. H. Freeman. ISBN 0-7167-5804-0. Retrieved on 2007-03-17. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger  
• Kirk Munsell:Solar System Exploration: Earth. NASA (October 19, 2006). Events 202 BCE - The Battle of Zama results in the defeat of Carthage and Hannibal. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Retrieved on 2007-03-17. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger
• Ward, Peter D. ; Donald Brownlee (2002). The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World. Times Books, Henry Holt and Company. ISBN 0-8050-6781-7.  
• Williams, David R. (September 1, 2004). Events 462 - Possible start of first Byzantine indiction cycle. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Earth Fact Sheet. NASA. Retrieved on 2007-03-17. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger
• Yoder, Charles F. (1995). in T. J. Ahrens: Global Earth Physics: A Handbook of Physical Constants. Washington: American Geophysical Union. ISBN 0875908519. Retrieved on 2007-03-17. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger  

External links

• USGS Geomagnetism Program
• NASA Earth Observatory
• Earth Profile by NASA's Solar System Exploration
• The size of Earth compared with other planets/stars
• Climate changes cause Earth's shape to change - NASA
• Geody Earth World's search engine that supports Google Earth, NASA World Wind, Celestia, GPS, and other applications. Google Earth is a Virtual globe program that was originally called Earth Viewer and was created by Keyhole Inc, a company acquired by Google in 2004 WorldWind is a free Open source Virtual globe developed by NASA and open source community for use on Personal computers running Microsoft Celestia is a 3-D Astronomy program created by Chris Laurel The program is based on the Hipparcos Catalogue (HIP and allows users to travel through an extensive