Earth — Introduction
Earth is the third planet from the Sun and the only known body in the Solar System that supports life. It is distinguished by globally persistent liquid surface water: the ocean contains almost all planetary water and covers about 70.8% of the crust, while the remaining 29.2% of the surface area is land, largely concentrated in continental masses within the planet’s land hemisphere. Terrestrial freshwater is dominated by polar ice sheets in the planet’s high-latitude deserts; these ice reservoirs store more water than the combined total held in groundwater, lakes, rivers, and the atmosphere.
The planet’s solid portion comprises a layered interior and a fractured outer crust divided into slowly drifting tectonic plates. Interactions among these plates give rise to mountain building, volcanism, and earthquakes. Beneath the mantle a convecting, liquid outer core generates a geomagnetic field that deflects much of the solar wind and cosmic radiation, while also responding to and modulating long-term rotational dynamics.
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Earth’s atmosphere — primarily nitrogen and oxygen with variable amounts of water vapor — is both protective and dynamic. It ablates most small meteoroids upon entry, attenuates harmful ultraviolet radiation, and sustains widespread cloud cover. Greenhouse gases, notably carbon dioxide along with water vapor, trap outgoing longwave radiation and maintain a mean surface temperature near 14.76 °C (58.57 °F), conditions under which water remains liquid at typical surface pressures. Latitudinal contrasts in incoming solar energy drive atmospheric and oceanic circulation, establish climate zones, and generate weather patterns (including precipitation) that underpin global biogeochemical cycles such as the carbon and nitrogen cycles.
Geometrically, Earth is an oblate spheroid with a circumference of roughly 40,000 km (24,900 mi); it is the densest known planet and, among the four terrestrial planets, the largest and most massive. The planet orbits the Sun at about 1 astronomical unit (≈8 light-minutes) and completes one revolution in roughly 365.25 days. It rotates in approximately 23 hours 56 minutes, and its axial tilt relative to the orbital plane produces seasonal variation in incident solar radiation.
Earth’s sole permanent natural satellite, the Moon, has a mean distance of about 384,400 km (238,855 mi; 1.28 light-seconds) and a diameter near one quarter that of Earth. Lunar gravity generates the principal tidal forces, contributes to long-term stabilization of Earth’s axial tilt, and exerts a torque that gradually slows Earth’s rotation. The Moon is tidally locked, with the same hemisphere continually facing Earth.
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Planetary formation and biospheric evolution unfolded over deep time: Earth accreted from the protoplanetary disk roughly 4.5 billion years ago; within the first billion years oceans formed and life emerged in marine settings. Biological activity progressively transformed the atmosphere and surface environments, most notably during the Great Oxidation Event about two billion years ago. Anatomically modern humans (Homo sapiens) arose in Africa ca. 300,000 years ago and subsequently dispersed globally. Human societies depend on Earth’s ecosystems and resources but have increasingly altered planetary systems, producing unsustainable impacts on climate and biodiversity that threaten livelihoods and are driving elevated rates of species extinction.
Etymology
The Modern English name Earth derives from Old English eorðe (Proto‑Germanic *erþō), a root attested across the Germanic family and originally applied to ground, dry land as opposed to water, the inhabited world, the surface of the globe, and ultimately the planet itself. In early English usage eorðe served as a functional equivalent to Latin terra and Greek gē, covering both literal soil and the broader concept of the world.
Germanic culture also personified the land: in late Norse myth the giantess Jörð (“Earth”) is portrayed as Thor’s mother, a feminine embodiment of the soil comparable to Roman Terra and Greek Gaia. Orthographically, the word has moved from routine lowercase through the Early Modern English practice of capitalizing “the Earth” in astronomical lists to the contemporary variability in which Earth is often capitalized when treated as a proper name but remains lowercase in idiomatic or nonspecific uses. Style guides differ (for example, Oxford tends to prefer lowercase while accepting a capitalized form); a common convention is to capitalize Earth in possessive or proper‑name contexts (“Earth’s atmosphere”) but to use lowercase after the definite article (“the atmosphere of the earth”), and idioms almost always retain lowercase.
Latinate and poetic alternatives appear in specialized registers: Terra (pron. /ˈtɛrə/, “TERR‑ə”) is frequent in scientific and science‑fiction contexts, and Tellus (pron. /ˈtɛləs/, “TELL‑əs”) occurs in poetic or classical usage. Romance languages preserve the Latin root in forms such as Italian/Portuguese Terra and in related forms like Spanish Tierra and French Terre. Greek‑derived names also persist: the Latinate Gaea (pron. /ˈdʒiː.ə/) is rare, while Gaia, revived in part by the modern Gaia hypothesis, is commonly pronounced /ˈɡaɪ.ə/ (occasionally /ˈɡeɪ.ə/), reflecting variation from the original Greek phonetics.
A productive set of adjectival derivatives documents these roots: from Earth come earthly; from Terra derive terran (/ˈtɛrən/), terrestrial (/təˈrɛstriəl/), and terrene (/təˈriːn/); and from Tellus derive tellurian (/tɛˈlʊəriən/) and telluric, each term occupying distinct semantic and stylistic niches when describing planetary or terrestrial attributes.
Formation
The Solar System originated when a portion of a molecular cloud underwent gravitational collapse and, conserving angular momentum, flattened into a rotating protoplanetary (solar) disk from which the Sun and all planetary bodies co-evolved. That disk contained gas, ice-coated grains and refractory dust carrying primordial nuclides, which served as the feedstock for progressive growth of solids and volatile reservoirs. Within this nebular environment small solid bodies—planetesimals—grew by collisional accretion and subsequently merged into planetary embryos and ultimately the planets.
High-precision radiometric and cosmochemical measurements anchor the earliest stages of this sequence: the oldest known Solar System solids have an age of 4.5682+0.0002 −0.0004 Ga. The Earth reached a recognizably planetary, differentiated state shortly thereafter, with formation constrained to about 4.54±0.04 Ga and accretion and primary differentiation likely occurring over tens of millions of years (roughly 70–100 Myr). The prevailing explanation for the Moon’s origin invokes a late, high‑energy, oblique collision in which a Mars‑sized body (commonly called Theia, ≈10% of Earth’s mass) struck the proto‑Earth; material from the impactor and Earth’s outer layers was launched into orbit and later aggregated to form the Moon. Estimates of the Moon’s formation age vary, however, and remain subject to interpretation of subsequent thermal and impact modification, although the giant‑impact and accretion scenario remains the favored mechanism.
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Between roughly 4.0 and 3.8 Ga the inner Solar System experienced a phase of intensified bombardment—the Late Heavy Bombardment—during which numerous large impacts drastically reworked the lunar surface; by analogy, this epoch would have produced profound contemporaneous disturbances of Earth’s surface environment.
After formation
Earth’s primary reservoirs of atmosphere and ocean water were established early through volcanic outgassing of the interior, with water vapor condensing to form oceans and additional volatiles delivered by asteroids, protoplanets and comets. Under this scenario enough water may have been present essentially from planetary formation, while elevated concentrations of greenhouse gases offset the reduced solar output of the young Sun and prevented global freezing. By the Archean, a geomagnetic field (established by ~3.5 Ga) also helped protect the atmosphere from erosion by the solar wind. Reconstructions of the early atmosphere indicate a methane-rich composition that would have imparted an orangeish appearance and produced a radiative environment quite different from the modern atmosphere.
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As the molten outer layer cooled the first solid crust was probably mafic; subsequent partial melting of that material generated more silica-rich (felsic) rocks that became the nuclei of primordial continental crust. Detrital and igneous studies, notably Hadean-age zircon grains preserved in Eoarchean sediments, demonstrate the presence of felsic, continental-like crust as early as ~4.4 Ga—only ~140 million years after Earth’s formation. Two end-member models account for continental growth: a roughly continuous, long-term increase in crustal volume and an alternative scenario of rapid crustal production concentrated in the Archean. These differing interpretations, drawn from radiometric ages and isotopic systems (e.g., Hf in zircons, Nd in sediments), can be reconciled if extensive recycling of crustal material—especially during the planet’s early history—substantially modified both volumes and isotopic signatures.
The generation and recycling of continental crust are intimately linked to plate tectonics, a surface expression of secular heat loss from Earth’s interior. Over hundreds of millions of years tectonic processes cause continental fragments to amalgamate into supercontinents and subsequently break apart, producing the long-term supercontinent cycle. Key Phanerozoic–Neoproterozoic events include the breakup of Rodinia beginning ~750 Ma, the transient assembly of Pannotia between ~600 and 540 Ma, and the later formation and fragmentation of Pangaea, which began disintegrating around 180 Ma.
Cenozoic climate evolution shows a long-term shift toward cooler conditions beginning roughly 40 Ma and an intensification of global glaciation in the Pleistocene from ~3 Ma onward. Since that time high- and mid-latitude regions have experienced repeated glacial–interglacial cycles paced primarily by Milankovitch periodicities of ~21,000, ~41,000 and ~100,000 years. The most recent major glacial interval, the Last Glacial Period, extended ice sheets to middle latitudes and ended approximately 11,700 years ago.
Origin of life and evolution
Life on Earth began at the molecular level in the early Archean, when abiotic chemistry yielded the first self-replicating molecules roughly four billion years ago; within several hundred million years a last universal common ancestor (LUCA) had appeared, providing the genetic foundation for subsequent diversification. Photosynthetic metabolisms evolved early as well, allowing organisms to capture solar energy and to release molecular oxygen; the progressive accumulation of O2 in the atmosphere enabled photochemical formation of an ozone layer that reduced surface ultraviolet flux and altered global redox conditions.
Cellular complexity increased through endosymbiotic events in which formerly free-living prokaryotes became integrated as organelles within host cells, producing eukaryotes capable of greater internal compartmentalization. Increasing cellular specialization and cooperative organization in colonies ultimately led to true multicellularity, opening morphological and ecological niches inaccessible to single-celled life. The combination of an ozone shield and other environmental changes facilitated expansion of life from marine habitats into shallow-water and terrestrial environments.
Geological and geochemical archives place traces of life deep in time: putative biogenic carbon in ca. 3.7 Ga Greenland rocks, stromatolitic microbial mats preserved in ca. 3.48 Ga Australian sandstones, and contested reports of biotic material as old as ca. 4.1 Ga indicate a protracted early record, with the oldest widely accepted microfossils appearing in ~3.45–3.5 Ga strata. The Archean surface was characterized by a cooling, water-rich crust with emergent continental crust, persistent volcanism, and extensive microbial mats (stromatolites) that contributed significantly to oxygen production.
Physical planetary conditions also influenced early ecosystems: following the Late Heavy Bombardment the Moon orbited much closer to Earth, producing tides far stronger than today and thereby affecting coastal and shallow-marine environments that were important for early life. Much later, during the Neoproterozoic (ca. 1000–539 Ma), Earth experienced extreme glaciations (the “Snowball Earth” hypothesis), an interval that directly preceded the rapid rise in body plans and ecological complexity in the Cambrian.
The Cambrian explosion, beginning around 535 Ma, marks a comparatively abrupt diversification of multicellular animals and ecosystems. Since then the biosphere has undergone repeated turnover, including at least five major mass extinctions; the most recent of these, the Cretaceous–Paleogene event at 66 Ma, was precipitated by an extraterrestrial impact that eliminated non‑avian dinosaurs and many large reptiles while disproportionately favoring smaller vertebrates and invertebrates, thereby reshaping terrestrial and marine communities.
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After the K–Pg crisis mammals radiated into diverse forms, and over the last several million years an African ape lineage evolved habitual bipedalism, which supported tool use, changes in diet and social behavior, and a trajectory of encephalization that culminated in anatomically and behaviorally modern humans. The advent of agriculture and the rise of complex societies initiated persistent, large‑scale anthropogenic alteration of Earth’s surface, biotic distributions, and evolutionary pathways—a transformation some researchers frame as driving a contemporary, human‑mediated biodiversity crisis.
Rising solar luminosity over the next billion to several billion years will drive a long‑term warming of Earth’s surface with major implications for climate and habitability. As surface temperatures increase, the inorganic carbon cycle will accelerate, drawing down atmospheric CO2 to levels incompatible with most modern plant physiology; models indicate CO2 could fall to the ~10 ppm threshold required for C4 photosynthesis within roughly 100–900 million years, jeopardizing global vegetation cover. The collapse of terrestrial and marine primary production would in turn reduce atmospheric O2, ultimately undermining the aerobic metabolisms that sustain contemporary animal life. Continued brightening of the Sun may elevate mean global temperatures to on the order of 100 °C in ~1.5 billion years, at which point liquid water and extant biospheric processes would largely cease to operate normally. Over the ensuing interval—approximately 1.6–3 billion years—ocean evaporation and hydrogen escape to space could drive a runaway greenhouse and the near‑complete loss of surface oceans, although some loss of ocean water to the mantle is also expected through reduced ridge outgassing and enhanced sequestration as Earth’s interior cools. On much longer timescales, when the Sun evolves into a red giant in roughly 5 billion years it will expand to a radius comparable to 1 AU; concomitant stellar mass loss of order ~30% would, absent strong tidal interactions, cause Earth’s orbit to migrate outward to about 1.7 AU. If tidal coupling between the swollen solar envelope and the planet is significant, however, Earth may be drawn into the expanding star, be vaporized, and have its constituents assimilated into the stellar interior.
Earth’s gross geometry reflects a balance between self-gravity and rotational forces: hydrostatic equilibrium produces an approximately rounded body with a mean diameter of about 12,742 km, making Earth the fifth largest planetary-sized object in the Solar System and the largest terrestrial planet. Rapid rotation deforms this idealized sphere into an oblate ellipsoid, yielding an equatorial bulge that increases the equatorial diameter relative to the polar diameter by roughly 43 km; as a result, points on the equator lie farther from Earth’s center than polar points. Local relief superimposed on the ellipsoid produces further departures from smoothness: Mount Everest rises about 8,848 m above local sea level (increasing the average radius by ≈0.14%), while the Mariana Trench plunges 10,925 m below local sea level (decreasing the average radius by ≈0.17%). Because of the equatorial bulge, the summit of Chimborazo in Ecuador is the single terrestrial point farthest from Earth’s center, at a radial distance of about 6,384.4 km, despite being lower than some more poleward peaks.
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Topography behaves differently on land and at sea: continental features (mountain ranges, trenches, volcanic edifices) are relatively static on human timescales, whereas the ocean surface is continually perturbed by tides, winds and currents. Geodesy therefore employs an idealized reference surface—the geoid—conceptualized as the equipotential surface the oceans would assume if they covered the entire planet and were free from dynamic disturbances. Using the geoid as the vertical datum provides a stable, physically based mean sea level against which elevations and depths are consistently measured, and it permits clear distinction between heights referenced to geocentric radial distance (distance from Earth’s center) and those given relative to mean sea level. Maps and analyses that use radial distance rather than the geoid thus produce different visual and quantitative portrayals of relief.
Surface
The Earth’s surface—the contact zone between the atmosphere and the solid Earth including the oceans—covers roughly 510 million km2 and exhibits the crust’s visible relief across continental land, continental shelves and ocean basins. Large-scale geographic division is commonly effected by two orthogonal schemes: latitudinally into Northern and Southern (polar) hemispheres and longitudinally into Eastern and Western (continental) hemispheres.
Marine realms dominate the planetary surface: about 70.8% (≈361 million km2) is occupied by the continuous global ocean, which in Earth’s history may at times have been nearly planet‑wide. Conventionally the ocean is partitioned, from largest to smallest, into the Pacific, Atlantic, Indian, Southern (Antarctic) and Arctic Oceans; these waters overlie oceanic crust and extend onto shelf seas above continental shelves. The ocean floor forms deep basins with an average depth near 4 km and varied bathymetry—abyssal plains, seamounts and submarine volcanoes, trenches and canyons, oceanic plateaus and a continuous mid‑ocean ridge system. Oceanic crust beneath sediments is predominantly basaltic.
Polar regions display seasonal sea‑ice cover that commonly interacts with adjoining permafrost, ice sheets and land to form polar ice caps; Antarctic conditions in particular present distinct sea‑ice cover over the Southern Ocean and an extensive Antarctic ice sheet over the continent.
Land comprises the remaining 29.2% of the surface (≈149 million km2), numerically many islands but spatially dominated by four major continental masses—Africa‑Eurasia, the Americas, Antarctica and Australia—which are further subdivided into continents. Terrestrial relief is highly variable, ranging from mountains and plateaus to plains and deserts: elevations span about −418 m at the Dead Sea to 8,848 m at Mount Everest, with a mean land height above sea level of roughly 797 m. Surface cover on land includes freshwater, seasonal snow and permanent ice, built infrastructure and vegetation; while most terrestrial area supports vegetation, significant portions are occupied by ice sheets (≈10% of land, not counting a comparable extent under permafrost) and deserts (≈33% of land), reflecting major contrasts in habitability and land‑use potential.
Soils—the pedosphere—constitute the outermost terrestrial layer and are fundamental for agriculture. Globally, about 10.7% of land is classified as arable, permanent cropland accounts for about 1.3%, and measured agricultural extents are on the order of 16.7 million km2 of cropland and 33.5 million km2 of pasture.
Together the land surface and ocean floor form the upper boundary of Earth’s crust; this crust and portions of the upper mantle constitute the lithosphere. Crustal types differ: oceanic crust is chiefly basaltic, whereas continental crust contains lower‑density materials such as granites, sediments and metamorphic rocks. Although sedimentary rocks cover nearly three‑quarters of continental surfaces, they represent only about 5% of the crust’s mass. Surface morphology is continually reshaped by internal plate‑tectonic forces (earthquakes, volcanism), external weathering and erosion agents (ice, water, wind, temperature) and biological processes (biomass growth and decomposition that contribute to soil formation).
Tectonic plates
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The lithosphere, comprising the crust and the uppermost mantle, forms Earth’s mechanically rigid outer shell and is broken into tectonic plates—coherent blocks that move relative to one another and constitute the fundamental units of plate tectonics. Plate interactions occur at three principal boundary types: convergent margins, where plates collide and one plate may be driven beneath another producing subduction zones, oceanic trenches, mountain-building, intense seismicity and volcanism; divergent margins, where plates separate and mantle upwelling generates new crust at mid‑ocean ridges; and transform margins, where lateral sliding between plates produces strike‑slip earthquakes.
Beneath the plates lies the asthenosphere, a mechanically weaker, ductile layer of the upper mantle that can flow slowly and thereby accommodates horizontal plate motions and associated mantle circulation. Oceanic lithosphere is continually renewed and recycled: new oceanic crust forms at spreading ridges and older oceanic crust is consumed at subduction zones, so most seafloor is geologically young (generally <100 Ma). The oldest preserved oceanic crust is found in the western Pacific and is roughly 200 Ma, whereas continental lithosphere can be far older—the oldest dated continental crust is about 4,030 Ma, and detrital zircons from Eoarchean sediments record ages up to ~4,400 Ma, indicating portions of continental crust existed by that time.
Global plate organization includes seven conventionally recognized major plates—the Pacific, African, North American, Eurasian, Antarctic, Indo‑Australian and South American plates—together with numerous smaller or regional plates such as the Arabian, Caribbean, Nazca and Scotia plates, whose interactions with the majors produce important regional tectonics. Plate configurations evolve through time (for example, the Australian and Indian plates amalgamated between ~50 and 55 Ma to form the Indo‑Australian Plate used in many reconstructions), and absolute motion rates vary substantially: oceanic plates commonly move fastest (the Cocos Plate ~75 mm/yr; the Pacific Plate ~52–69 mm/yr), whereas some continental plates advance more slowly (the South American Plate typically ~10.6 mm/yr).
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Internal structure of the Earth is organized into concentric shells defined both by chemical composition and by rheological behavior. From the surface inward these are the crust, mantle, outer core and inner core; mechanically distinct shells such as the lithosphere (rigid crust plus uppermost mantle) and the underlying, relatively low‑viscosity asthenosphere couple these compositional layers and govern their dynamical interactions.
The silicate crust—separated from the underlying mantle by the Mohorovičić discontinuity—varies markedly in thickness, averaging roughly 6 km beneath oceans and about 30–50 km beneath continents (crustal layer conventionally 0–35 km in global models). Together with the cold, rigid portion of the uppermost mantle the crust forms the lithosphere (extending to ~0–60 km), which is segmented into independently moving tectonic plates.
Beneath the lithosphere the asthenosphere is a mechanically soft, low‑viscosity zone (commonly placed between ~100 and 700 km depth) that permits plate motion. The mantle is conventionally divided at mineral‑phase boundaries near ~410 km and ~660 km (the mantle transition zone). The upper mantle (≈35–660 km) has bulk densities ~3.4–4.4 g·cm−3 and contains the lithospheric lid above the more deformable asthenosphere; the lower mantle (≈660–2,890 km) experiences progressively higher pressures and phase changes and shows increasing density up to ~5.6 g·cm−3.
The core is chemically distinct and dominated by iron‑rich phases. A convecting, very low‑viscosity liquid outer core occupies ≈2,890–5,100 km depth with densities ≈9.9–12.2 g·cm−3 and drives the geodynamo that generates Earth’s magnetic field. The inner core is solid, extends from ≈5,100 km to the centre at ≈6,378 km (radius ≈ one‑fifth of Earth’s radius), and has densities ≈12.8–13.1 g·cm−3. Seismic and geomagnetic analyses suggest the inner core may rotate slightly more rapidly than the mantle and crust (order 0.1–0.5° yr−1, though estimates vary).
Throughout the mantle and into the core both pressure and density increase continuously with depth, producing the tabulated density gradients; among Solar System terrestrial bodies Earth exhibits the highest mean density.
Earth’s mass is about 5.97 × 10^24 kg, a fundamental constraint for models of its internal structure and chemical inventory. On a whole‑Earth basis, a small suite of elements comprises nearly the entire mass: iron (≈32.1%), oxygen (≈30.1%), silicon (≈15.1%), magnesium (≈13.9%), sulfur (≈2.9%), nickel (≈1.8%), calcium (≈1.5%), and aluminium (≈1.4%), with the remaining ~1.2% made up of trace constituents.
Early and ongoing gravitational differentiation segregated denser materials toward the centre and lighter, silicate‑forming elements toward the exterior. As a result, the core is overwhelmingly metallic—primarily iron (≈88.8%) with subordinate nickel (≈5.8%), sulfur (≈4.5%) and only trace other elements. In contrast, the crust and mantle are dominated by silicate and oxide minerals: more than 99% of the crustal mass occurs as oxides of about eleven elements. Silicon (in silicate frameworks), aluminium, iron, calcium, magnesium, potassium and sodium in particular define the principal mineralogy of the planet’s outermost solid layer.
Internal heat
Earth’s internal heat is sustained primarily by two reservoirs: primordial heat retained from accretion and differentiation, and radiogenic heat produced by the decay of isotopes—notably potassium‑40, uranium‑238 and thorium‑232. Because a large fraction of heat production is radiogenic, the planet’s heat output has declined through time as short‑lived isotopes decayed; around 3 billion years ago overall heat production was roughly twice the present rate, a condition that intensified mantle convection and plate‑tectonic activity and permitted the generation of high‑temperature magmas such as komatiites that are rare today.
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Extreme conditions at Earth’s center—temperatures possibly approaching 6,000 °C and pressures on the order of 360 GPa—constitute the deep thermal reservoir that drives large‑scale convective motion in the mantle and core. Thermal energy from this reservoir reaches the crust by several interacting processes. Mantle plumes are buoyant upwellings that transport anomalously hot rock from the core‑mantle region toward the lithosphere and produce localized surface expressions (hotspots, flood basalt provinces). On a broader scale, plate‑tectonic circulation is the principal mechanism of planetary heat loss: divergent margins and upwelling at mid‑ocean ridges expel vast volumes of heat and create new oceanic lithosphere, making ridge‑related upwelling the single largest pathway for internal heat release.
Surface heat flow exhibits a clear spatial pattern tied to these transport processes. Mid‑ocean ridge systems are the main corridors for upward heat transport and therefore show markedly higher surface heat flow than continental interiors; the thinner, younger oceanic lithosphere also promotes higher conductive flux beneath oceans. Conduction through the lithosphere is the terminal mode by which internal heat reaches the surface, and it is concentrated where lithospheric thickness is minimal. The present‑day mean surface heat flux is about 87 mW m−2, corresponding to a total global heat loss of approximately 4.42 × 10^13 W.
Gravitational field
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Earth’s gravity is the acceleration experienced by masses due to the combined attraction of the planet’s internal mass distribution; at any location the local acceleration results from the integrated pull of material throughout the body rather than from a single point source. The canonical near-surface value of this gravitational acceleration is about 9.8 m s−2, which serves as an average reference for objects close to the surface. Measured gravity, however, is spatially variable: both small-scale and broad regional departures from this mean arise because differences in topography, near-surface rock and sediment densities, and deeper tectonic structures change the distribution of mass. Such departures are expressed as gravity anomalies—positive or negative deviations from an expected field—and they provide a primary geophysical tool for inferring subsurface mass contrasts and interpreting geological and tectonic architecture at local to regional scales.
Magnetic field
Earth’s dominant magnetic field is generated by a self-sustaining dynamo in the electrically conducting, fluid outer core, where convective motions driven by thermal and compositional buoyancy convert kinetic energy into electrical currents and magnetic energy. The resulting internal field penetrates the mantle and, to first order, resembles a dipole oriented near the geographic rotation axis. At the magnetic equator the field magnitude is about 3.05×10−5 T, and the global dipole moment was 7.79×10^22 A·m^2 at epoch 2000; this moment has been declining at roughly 6% per century, although it remains above its long-term mean. Chaotic variations in core convection produce secular changes in field strength and pole position, and occasional complete polarity reversals occur at irregular intervals averaging a few times per million years, the most recent reversal having taken place ~700,000 years ago.
The region in which the geomagnetic field governs charged-particle motion—the magnetosphere—is shaped by the dynamic interaction with the solar wind. Solar-wind ram pressure compresses the dayside magnetosphere to approximately 10 Earth radii and elongates the nightside into a magnetotail; because the solar wind is supersonic relative to magnetohydrodynamic signal speeds, a bow shock forms upstream and decelerates and heats the flow before it encounters the magnetic obstacle. The magnetosphere thus deflects much of the solar-wind plasma while mediating energy and momentum transfer into near‑Earth space.
Within the magnetosphere distinct particle populations are organized by energy and dominant motions. Low-energy plasma largely co-rotates with Earth in the plasmasphere and follows field lines, medium-energy particles form the ring current as they drift under geomagnetic forces, and high-energy particles occupy the Van Allen radiation belts where their trajectories are strongly influenced but effectively randomized by the magnetic field. During geomagnetic storms and substorms, energy stored in the outer magnetosphere and magnetotail can be released, injecting energetic particles along field lines into the upper atmosphere; collisions there produce excitation and ionization that generate the visible auroral displays.
Rotation
Earth’s daily spin is directly observable in satellite time‑lapse imagery, which records the planet’s diurnal rotation and makes evident the axial tilt that produces the latitudinal pattern of seasonal solar illumination. The conventional mean solar day—the interval by which civil time is defined—is 86,400 seconds of mean solar time and corresponds to 86,400.0025 SI seconds; long‑term tidal deceleration since the nineteenth century has slightly increased day length so that individual solar days now typically exceed that mean by up to a few milliseconds. Measured against the fixed stars, the rotation period (the stellar day, as reported by the IERS) is 86,164.0989 seconds of mean solar time (UT1), or 23 h 56 m 4.0989 s. Measured instead relative to the precessing mean March equinox (the conventional sidereal day), the interval is 86,164.0905 seconds UT1 (23 h 56 m 4.0905 s), about 8.4 ms shorter than the IERS stellar day.
Because Earth rotates eastward, most celestial objects appear to move westward across the sky at an angular rate of 15° per hour (equivalently 15′ per minute); meteors within the atmosphere and low‑orbit satellites are notable exceptions to this general motion. For sources near the celestial equator that angular speed implies an apparent traversal equal to the angular diameter of the Sun or Moon in roughly two minutes. From the Earth’s surface the Sun and Moon have similar apparent diameters, so equatorial transits of objects subtending the same angle have comparable transit times.
Orbit
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Earth orbits the Sun as the third planet of the inner Solar System at a mean distance of ≈1 astronomical unit (AU), about 150 million km (93 million mi), which corresponds to ≈8.3 light‑minutes or roughly 380 times the mean Earth–Moon separation. The orbital period about the Sun is 365.2564 mean solar days (one sidereal year), during which the Sun appears to move eastward along the ecliptic at ≈1° per day; this apparent motion underlies the mean solar day of ≈24 hours. Mean orbital speed is ≈29.7827 km s−1 (≈107,218 km h−1), a velocity that would carry Earth one planetary diameter in about seven minutes and span the Earth–Moon distance in roughly 3.5 hours.
The Earth–Moon pair revolve about their common barycenter with a sidereal period of 27.32 days; when this motion is combined with the system’s progression around the Sun the interval between successive new moons (the synodic month) becomes 29.53 days. Observed from above the celestial north pole, the rotations and orbital motions of both Earth and Moon are counterclockwise, as is Earth’s motion about the Sun when viewed from above the Sun’s north pole.
Orbital and rotational planes are mutually inclined: Earth’s rotation axis is tilted ≈23.44° from the perpendicular to the ecliptic, while the Moon’s orbital plane is inclined by up to ≈5.1° to the ecliptic. Because seasonal extremes (equinoxes and solstices) are determined by axial tilt rather than instantaneous Sun–Earth distance, the orbital apsides (perihelion and aphelion) do not coincide with seasonal extrema; likewise the ±5.1° lunar inclination prevents eclipses at every conjunction and opposition, which would otherwise occur roughly every two weeks. Earth’s region of dominant gravitational control (its Hill sphere) extends to about 1.5×10^6 km (≈930,000 mi); satellites must remain within this radius to be stably bound against solar and planetary perturbations.
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On larger scales, the Solar System—including Earth—orbits the center of the Milky Way at a galactocentric radius of roughly 28,000 light‑years and lies some ≈20 light‑years above the Galactic plane within the Orion Arm.
Axial tilt and seasons
Earth’s rotational axis is inclined by approximately 23.439281° to the plane of its orbit (the ecliptic) and is directed toward the celestial poles. This obliquity causes systematic, latitude‑dependent changes in both the solar elevation angle and the duration of daylight over the course of an orbital year, producing the familiar sequence of seasons. When the Tropic of Cancer is tilted toward the Sun the Northern Hemisphere receives higher solar altitudes and longer days (summer) while the Southern Hemisphere receives lower solar altitudes and shorter days (winter); the situation reverses when the Tropic of Capricorn is tilted sunward.
At high latitudes these effects are extreme: areas above the Arctic and below the Antarctic Circles undergo intervals of continuous daylight (midnight sun) and intervals of no direct daylight (polar night), and the poles themselves can remain sunlit or dark for months. Seasons are conventionally bounded by the solstices—points of maximum tilt toward or away from the Sun—and the equinoxes—when the Sun crosses the equatorial plane and day and night are approximately equal. In the Northern Hemisphere the winter solstice now falls near 21 December, the summer solstice near 21 June, the vernal equinox about 20 March, and the autumnal equinox about 22–23 September; the Southern Hemisphere experiences the opposite timing.
The orientation of Earth’s axis is not immutable. Superimposed on the constant obliquity are an 18.6‑year nutation and a steady gyroscopic precession with a period of roughly 25,800 years; precession alters the axis’s orientation in space (but not the instantaneous tilt angle) and is responsible for the difference between the sidereal and tropical year. These motions, together with gravitational torques exerted by the Sun and Moon on Earth’s equatorial bulge, also induce smaller quasiperiodic displacements of the geographic poles by a few meters; this polar motion includes an annual component and the approximately 14‑month Chandler wobble. Earth’s rotation rate itself varies on multiple timescales, producing measurable changes in day length and contributing to the full suite of rotational and polar variations that influence precise geodetic positions.
Finally, Earth’s orbit is elliptical rather than circular: perihelion presently occurs near 3 January and aphelion near 4 July, though these dates and eccentricity evolve under long‑term orbital cycles (Milankovitch forcing). The variation in Sun–Earth distance alters incident solar power by roughly 6.8% between perihelion and aphelion; because perihelion currently coincides with Southern Hemisphere summer, that hemisphere receives a small annual surplus of solar energy. This orbital distance effect, however, is minor compared with the latitudinal redistribution of insolation produced by axial tilt, and much of the Southern Hemisphere’s modest excess is moderated by its larger ocean fraction.
Moon
The Moon is a comparatively large, terrestrial natural satellite of Earth, with a diameter roughly one quarter that of its primary. Relative to the size of its host planet it is the largest satellite in the Solar System, although comparable relational metrics (for example Pluto–Charon) vary with the scale of the primary body. By convention, natural satellites of other planets are commonly termed “moons” by analogy with Earth’s companion.
The prevailing formation model is the giant‑impact hypothesis: a collision between the proto‑Earth and a Mars‑sized body (Theia) produced a debris disk from which the Moon accreted. This scenario accounts for the Moon’s relative depletion in iron and volatile elements and for its bulk compositional similarity to Earth’s crust. Numerical impact simulations further suggest that vestiges of Theia may persist as blob‑like heterogeneities embedded within Earth’s deep interior.
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Gravitational interaction between Earth and the Moon drives Earth’s oceanic tides and has synchronized the Moon’s rotation with its orbital period (tidal locking), so the same lunar hemisphere faces Earth continuously. The cycle of lunar phases arises from the changing geometry of Sun–Earth–Moon illumination as the Moon orbits Earth. Because the Sun is about 400 times wider and about 400 times more distant than the Moon, the two bodies present nearly the same apparent angular size in Earth’s sky, permitting both total and annular solar eclipses.
Tidal torques also produce long‑term dynamical evolution of the system: the Moon is currently receding from Earth at roughly 38 mm per year, while Earth’s rotation slows by about 23 microseconds per year. Integrated over deep time, these rates yield measurable changes in Earth–Moon dynamics; for example, reconstructions for the Ediacaran (≈620 Ma) imply about 400 ± 7 days per year with a day length near 21.9 ± 0.4 hours. The Moon’s tidal influence further contributes to stabilizing Earth’s axial tilt (obliquity), moderating long‑term climate variability by resisting torques from other bodies acting on Earth’s equatorial bulge, though the magnitude and necessity of this stabilizing role remain subjects of ongoing discussion.
Asteroids and artificial satellites
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A computer-generated global map of Earth orbit highlights two principal regimes in which human-made objects concentrate: a ring-like clustering near geosynchronous altitudes and a denser, more spatially diffuse population in low Earth orbit (LEO). This anthropogenic environment comprises thousands of active systems—4,550 operational satellites as of September 2021—together with numerous inactive satellites (including Vanguard 1, the oldest object still aloft) and over 16,000 pieces of tracked debris. Among artificial constructs, the International Space Station is the largest and most massive single object in Earth orbit, while the combined inventory of functioning, defunct, and fragmented hardware defines the contemporary near-Earth debris environment.
Natural co-orbital companions of Earth fall into three dynamical categories: quasi-satellites, objects on horseshoe-type trajectories, and trojan companions. Each class denotes a distinct gravitational relationship with Earth while the small body shares or closely parallels Earth’s heliocentric path. Quasi-satellites are temporarily bound in a 1:1 mean-motion relationship and at least seven such objects are known, with diameters spanning roughly 10 m to 5,000 m; 469219 Kamoʻoalewa is a representative example. Horseshoe objects execute extended, kidney-shaped relative trajectories that alternate in proximity to Earth, whereas trojans occupy the stable triangular Lagrange regions; the asteroid 2010 TK7 is a confirmed Earth trojan librating about the leading L4 point, approximately 60° ahead of Earth.
Transient near-Earth asteroids can exhibit episodic interactions with the Earth–Moon system. The small body 2006 RH120, for example, follows a dynamically unstable path that brings it into close approach on an approximate 20‑year cadence and, during some encounters, permits temporary capture into short-lived orbits about Earth. These natural co-orbitals, together with the dense anthropogenic population in LEO and the concentrated band near geosynchronous altitude, underscore the complexity of near-Earth space as both a natural dynamical environment and a heavily utilized orbital domain.
Hydrosphere
Earth’s hydrosphere denotes the totality of water on and around the planet and its spatial arrangement, dominated at the surface by a contiguous global ocean and widespread cloud cover, with extensive polar ice concentrating water into large, high-latitude reservoirs. It includes the global ocean together with atmospheric water (vapor and clouds), surface freshwater bodies (lakes, rivers, inland seas), groundwater, permafrost, glacial ice and biologically bound water.
The global ocean contains roughly 1.35 × 10^18 metric tons of water—about one part in 4,400 of Earth’s total mass—and covers approximately 361.8 million km^2 with a mean depth of about 3,682 m, yielding an estimated volume near 1.332 × 10^9 km^3. If redistributed to a uniform elevation across a smooth spherical Earth, this ocean layer would be about 2.7–2.8 km deep. Seawater is largely saline (average salinity ≈ 35 g of dissolved salts per kg, or 3.5%); about 97.5% of Earth’s water is saline while only about 2.5% is fresh. Most marine salts originate from volcanic outgassing and chemical weathering of igneous rocks.
Seawater functions as both a chemical and climatic reservoir: it stores dissolved gases necessary for aquatic life and holds large amounts of heat, thereby buffering atmospheric temperature fluctuations. Variations in ocean temperature and its spatial distribution can drive major climate and weather phenomena, exemplified by oscillations such as El Niño–Southern Oscillation.
Freshwater is heavily sequestered in cryospheric and subsurface stores. Of the ~2.5% of water that is freshwater, roughly 68.7% is locked in ice caps and glaciers, about 30% resides as groundwater, and only about 1% exists as surface freshwater—which itself occupies only some 2.8% of Earth’s land area. The remainder is distributed among permafrost, atmospheric vapor and biotic water pools. In cold regions, accumulated seasonal snow compacts into glacier ice that, under its own weight, flows; alpine glaciers form in mountains while continental ice sheets develop over polar landmasses. Glacier motion and associated processes erode bedrock and sculpt characteristic landforms such as U-shaped valleys.
Polar sea ice is a dynamic component of the hydrosphere: Arctic sea ice historically has covered an area comparable to the size of the United States, but it is diminishing rapidly in extent and volume under contemporary climate warming.
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Comparatively within the Solar System, Earth’s abundance of stable liquid surface water is exceptional. Other planets with substantial atmospheres may contain water vapor but generally lack conditions for persistent surface liquids; some moons exhibit evidence for very large subsurface liquid reservoirs—potentially exceeding Earth’s ocean volume—but these lie beneath kilometers of frozen crust and are not surface-accessible.
Atmosphere
Viewed from space, Earth’s atmosphere appears layered: the lowest layer, the troposphere, contains the visible cloud systems that cast shadows onto lower layers and the surface; beyond it a thin stratospheric band of blue defines the horizon; and a narrow green airglow produced in the lower thermosphere near 100 km altitude marks the conventional edge of space. Mean sea‑level pressure is 101.325 kPa (14.696 psi), and pressure falls exponentially with height with a scale height of roughly 8.5 km.
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Excluding variable water vapor, the atmosphere is dominated by permanent gases: nitrogen (~78.084% by volume) and oxygen (~20.946%), with argon near 0.934% and trace concentrations of CO2 and other species. Water vapor itself varies strongly in space and time—about 0.01–4% by volume, averaging near 1% globally—and this variability largely determines local humidity and cloud formation. Clouds cover approximately two‑thirds (~66%) of the planet at any moment, more extensively over oceans than land, which influences planetary albedo and the redistribution of heat.
The troposphere’s thickness changes with latitude and weather: it is typically about 8 km near the poles and expands to about 17 km near the equator, with additional short‑term variability associated with meteorological systems. Over geological time the biosphere has profoundly remodeled atmospheric composition: the evolution of oxygenic photosynthesis around 2.7 billion years ago led to the buildup of molecular oxygen and a shift toward the present nitrogen–oxygen dominated atmosphere. This oxygenation enabled the radiation of aerobic life and, via photochemical conversion of O2 to O3, the development of an ozone layer that absorbs much ultraviolet radiation and thereby facilitated terrestrial colonization.
Functionally, the atmosphere transports water and gases essential to life, causes small meteors to ablate before they reach the surface, and moderates surface temperatures through the greenhouse effect. The principal greenhouse constituents are water vapor, carbon dioxide, methane, nitrous oxide, and ozone; without their heat‑retaining influence the global mean surface temperature would be about −18 °C rather than the present ≈+15 °C, a difference that has been crucial for the emergence and persistence of extant ecosystems.
Weather and climate
Earth’s atmosphere grades gradually into space rather than ending at a distinct boundary; about three-quarters of its mass resides in the lowest layer, the troposphere, which reaches roughly 11 km above the surface. Solar radiation delivered to the top of the atmosphere averages about 1361 W m−2, but the portion that penetrates to the surface declines with latitude because sunlight arrives at lower angles and traverses a thicker atmospheric column. Absorption of solar energy by the surface and lower atmosphere produces buoyant, rising air and compensating inflows of cooler air, generating convective circulation that redistributes heat and establishes the dynamical basis of weather and climate.
Large-scale atmospheric circulation organizes global wind and moisture regimes: the trade winds dominate the tropics below about 30° latitude, while the westerlies prevail in mid-latitudes between roughly 30° and 60°. Oceans complement the atmosphere in setting climate; currents and ocean heat storage, including the thermohaline circulation that transports warmth poleward from equatorial basins, substantially moderate regional and global temperature patterns and influence climatic variability.
The geometrical pattern of insolation produces a systematic latitudinal temperature gradient: mean annual sea-level air temperature declines by roughly 0.4 °C per degree of latitude away from the equator, allowing conceptual division into tropical, subtropical, temperate, and polar belts. Proximity to large water bodies reduces seasonal temperature range because oceans store and slowly release heat; consequently maritime coasts tend to have cooler summers and milder winters than continental interiors. Local climate examples illustrate these effects: San Francisco and Washington, D.C., lie at similar latitudes, yet San Francisco’s onshore prevailing winds convey ocean-moderated air and produce a markedly more equable climate.
Topography further modifies temperature and precipitation. Temperature decreases with altitude (lapse-rate effects), making high-relief regions systematically cooler than adjacent lowlands, and orographic uplift of moist air yields enhanced precipitation on windward slopes and rain-shadow aridity on leeward sides. The hydrological cycle—evaporation, atmospheric transport, uplift and condensation, precipitation, and riverine return to oceans or lakes—connects energy and mass fluxes, sustains terrestrial ecosystems, and drives landscape erosion over geological timescales. Resulting precipitation totals vary enormously across the globe, from several meters per year in the wettest locations to less than a millimetre per year in the driest deserts.
Climate classification and extremes reflect these controls. The Köppen scheme partitions climates into five principal groups—humid tropics, arid, humid middle latitudes, continental, and cold polar—with further subtypes based on observed temperature and precipitation regimes. Measured surface-air extremes exemplify Earth’s climatic range: daytime maxima in hot deserts can approach about 55 °C (e.g., Death Valley), whereas the lowest recorded surface temperatures reach approximately −89 °C in Antarctica.
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Upper atmosphere
From orbit at night, Earth’s upper atmosphere appears as a series of concentric luminous bands. The lowest glow, associated with the troposphere, often appears orange with cloud silhouettes; above it the stratosphere shows paler white and blue tones; the mesosphere can appear pink and grades upward into a thin orange–green airglow layer near 100 km altitude, which approximates the lower boundary of the thermosphere; at still greater heights auroral displays produce broad green and red curtains extending for hundreds of kilometres.
Conventionally, the region above the troposphere is subdivided into stratosphere, mesosphere and thermosphere, each distinguished by a characteristic lapse rate (the sign and magnitude of temperature change with height) so that temperature profiles differ markedly between these layers. The stratosphere contains the ozone layer, a concentrated reservoir of O3 that absorbs much of the Sun’s ultraviolet radiation and thereby mitigates surface UV exposure, with important implications for life.
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The Kármán line, set at 100 km above mean sea level, is a practical frontier between atmosphere and space and coincides roughly with the lowest persistent airglow emission noted at that altitude. Above the thermosphere the gas becomes progressively tenuous, passing into the exosphere and, where planetary magnetic fields dominate, the magnetosphere; in these outer regions geomagnetic structures govern the motion of charged particles and mediate interactions with the solar wind.
Thermal (kinetic) energies in the rarified outer atmosphere can accelerate individual molecules to velocities exceeding Earth’s escape speed, producing a slow, cumulative loss of atmospheric mass over geologic time. Light species—above all atomic and molecular hydrogen—attain escape velocity far more readily than heavier constituents because of their low mass, so hydrogen is lost preferentially. This selective escape has important redox consequences for the planet: removal of reducing hydrogen made it possible for surface and atmospheric chemistry to shift from an originally reducing state toward the oxidizing conditions required for the long-term accumulation of free oxygen produced by photosynthetic organisms. Thus the pace at which hydrogen could be removed from the atmosphere likely influenced the timing and character of Earth’s oxygenation and, by extension, the trajectory of biological evolution.
In the modern, oxygen-rich atmosphere most free hydrogen is rapidly incorporated into water and so is protected from direct escape; consequently, a principal pathway for continued hydrogen loss today is indirect, via photochemical destruction of methane (CH4) in the upper atmosphere, which liberates hydrogen atoms that can subsequently escape to space.
Life on Earth
Global maps of primary productivity highlight stark spatial and temporal contrasts between terrestrial and marine primary producers: vegetation density on land is commonly rendered from low (brown) to high (dark green), while surface phytoplankton concentration in the oceans is shown from low (purple) to high (yellow), illustrating different centers of biological production and their variability through time.
Life emerged in Earth’s waters within a few hundred million years after planetary formation and, from these localized beginnings, expanded into freshwater, terrestrial and open-ocean habitats to form an interconnected, planetary-scale biosphere. Biological processes have not merely responded to physical conditions but have driven profound planetary transformations over geological time—for example, the Great Oxidation Event fundamentally altered atmospheric composition and surface geochemistry.
The biosphere is partitioned into broad biomes—assemblages of organisms with similar ecological characteristics—whose distributions are governed chiefly by gradients of elevation or water depth, climate (principally temperature and latitude), and, for terrestrial systems, moisture availability. Accordingly, biomass and species richness concentrate under warm, humid, equatorial conditions and in shallow marine environments and forests, whereas polar regions, high-elevation zones and hyper-arid areas support comparatively low biological abundance and diversity.
Liquid water is the medium that facilitates assembly and interaction of complex organic molecules, provides the energetic and chemical conditions required for metabolism, and enables organisms to obtain nutrients from soils, water and the atmosphere. These nutrients are continuously cycled among species and ecosystem compartments, linking biological function to geochemical and hydrological processes.
Atmospheric and oceanic circulation, seasonal rhythms and synoptic weather systems drive ecological variability and produce extreme events—such as intense tropical cyclones—that concentrate energy and cause widespread environmental and societal impacts. Between 1980 and 2000, meteorological and hydrological extremes accounted for an average of about 11,800 human deaths per year, underscoring the substantial human vulnerability to climate and weather hazards.
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In addition to climate-driven extremes, a spectrum of geophysical hazards—earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, blizzards, floods and droughts—along with biological disturbances like wildfires, periodically reshape landscapes, redistribute sediments and nutrients, and impose acute risks on human communities and ecosystems.
Human activity has produced pervasive environmental change: air- and water-pollution, acid deposition, vegetation loss through overgrazing, deforestation and desertification, species declines and extinctions, and widespread soil degradation and erosion. By altering biogeochemical cycles and releasing greenhouse gases to the atmosphere, humans are driving global warming with observable and projected consequences including glacial and ice-sheet melt, global sea-level rise, higher risks of drought and wildfire, and shifts in species distributions toward higher latitudes and elevations as organisms seek suitable climates.
Human geography
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Night-time satellite imagery of artificial lighting provides a powerful observational proxy for the global human footprint: it spatially concentrates where population density, urbanization and economic infrastructure are greatest, especially in coastal belts and metropolitan regions. This visible pattern reflects a highly uneven distribution of people—most inhabitants are found in South and East Asia, and roughly 90% of the world’s population lives in the Northern Hemisphere, a bias partly explained by the Northern Hemisphere containing about 68% of terrestrial land. Since the 19th century a sustained rural-to-urban transition has concentrated populations and economic activity in cities, a process manifested in the intensification of nocturnal light emissions.
Homo sapiens originated in eastern Africa approximately 300,000 years ago and subsequently dispersed worldwide; the transition to sedentary, agricultural societies in the 10th millennium BC markedly accelerated settlement density and the formation of complex societies. Global population growth became exponential from the 19th century onward, reaching about 8 billion in the 2020s, with demographic models projecting a peak near ten billion during the second half of the 21st century and most future growth concentrated in sub‑Saharan Africa.
Political and spatial control of terrestrial territory has likewise become nearly comprehensive: since the 19th century most land has been incorporated into sovereign states (about 205 recognized today), with only portions of Antarctica and a few small areas remaining outside national claims. The United Nations serves as the principal global intergovernmental body through which states coordinate governance extending over oceans and Antarctica. Outside Earth’s surface, human presence is extremely limited to specialized underground and underwater facilities, a handful of space stations and—since the mid‑20th century—several hundred individuals who have left Earth, only a very small number of whom have visited another celestial body (the Moon); the vast majority of humanity remains on and dependent upon Earth’s environments.
Natural resources and land use
Earth’s crust concentrates non‑renewable geological resources that renew only over geological timescales. Chief among these are fossil fuels—coal, petroleum and natural gas—which serve both as primary energy sources and as feedstocks for chemical industries. Metal ore bodies form through ore‑genesis processes driven by magmatic activity, erosion and plate‑tectonic forces; the extraction of these metal‑bearing deposits by mining frequently produces substantial environmental degradation and poses public‑health risks.
The terrestrial biosphere furnishes essential ecosystem services and commercial goods—food, timber, medicines, oxygen and the biological processing of organic waste—services that depend critically on soil health and the availability of freshwater in land ecosystems. Marine productivity is intimately connected to land processes because rivers and runoff transport dissolved nutrients from terrestrial surfaces to the oceans; thus land management and upstream nutrient fluxes are key controls on coastal and open‑ocean ecosystems.
Global land‑cover and land‑use patterns quantify the large spatial footprint of these natural resources and human activities. In 2019 forests and woodlands occupied about 39 million km2, serving as major reservoirs of carbon and biodiversity. Shrublands and grasslands covered roughly 12 million km2, providing extensive habitat, grazing potential and other ecosystem services. Land devoted to grazing and animal‑feed production amounted to about 40 million km2, a land area comparable in magnitude to global forests. Croplands encompassed approximately 11 million km2, equivalent to about 12–14% of ice‑free land; of ice‑free land, about 2 percentage points were irrigated as of 2015, underscoring irrigation’s role in contemporary crop production.
Beyond energy and food, humans extract geological and biological materials for construction, linking resource extraction directly to settlement patterns and infrastructure. Taken together, these resource stocks and land uses illustrate the extensive and varied imprint of human activity on Earth’s surface and the biophysical interconnections among geology, terrestrial ecosystems and the oceans.
Human influence now accounts for the long-term increase in global mean surface air temperature, with natural variability superimposed on that trend. The dominant anthropogenic pathway is the combustion of fossil fuels, which elevates atmospheric greenhouse‑gas concentrations and thereby perturbs Earth’s radiative balance and climate system. By 2020, global mean temperatures had risen about 1.2 °C above preindustrial levels, a change commonly termed global warming.
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Observed warming has already driven substantive physical and ecological responses: widespread glacier retreat and consequent sea‑level rise, heightened exposure to drought and wildfire risk, and shifts in species distributions toward higher latitudes and elevations as organisms track cooler conditions. These changes are symptomatic of broader human pressures on Earth-system functioning, which are quantified by the planetary boundaries framework. That framework defines nine critical Earth-system processes; five of these have been exceeded—biosphere integrity, climate change, chemical pollution, loss of wild habitats, and the nitrogen cycle—placing them beyond thresholds considered safe for long‑term system stability.
An assessment through 2018 found that no country simultaneously satisfies the basic material and social needs of its population while remaining within planetary boundaries, indicating a global failure to provide for human well‑being without overshooting environmental limits. Nevertheless, analyses conclude it is feasible to meet all basic physical needs for the global population within sustainable resource use if appropriate technological, policy, and behavioral changes are implemented to reduce pressures and operate within the safe boundaries.
Human cultures have long encoded ideas about Earth in symbols, myths and rituals. Astronomical emblems such as the quartered circle—evoking the “four corners” of the world—and the globus cruciger have served as visual shorthand for the planet in both secular and religious iconography. Many traditions also personify Earth as a living being, frequently a mother or fertility deity, and origin stories across diverse religions attribute the world’s creation to one or more supernatural agents.
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Scientific revolutions progressively transformed those cultural and cosmological conceptions. The ancient Greek transition from a flat‑earth cosmology to recognition of a spherical Earth—often associated in historical accounts with figures like Pythagoras and Parmenides—reframed human geography in geometric terms. For much of recorded history Earth was regarded as the fixed center of the universe; during the sixteenth century the Copernican turn established that Earth is a moving planet orbiting the Sun. Nineteenth‑century geology and physics then extended temporal horizons: stratigraphic reasoning required vast antiquity, while Lord Kelvin’s thermodynamic calculations (mid‑19th century) provoked intense debate by yielding age estimates far shorter than those later demonstrated. The discovery of radioactivity and development of radiometric dating around the turn of the twentieth century ultimately provided a robust basis for an Earth measured in billions of years.
In the twentieth century new conceptual and observational frameworks further altered perspectives on Earth as a system. The Gaia hypothesis proposed that biotic and abiotic components interact to produce self‑regulating feedbacks that stabilize conditions for life, encouraging integrative thinking about planetary processes. Concurrently, imagery and measurements from space fundamentally changed both scientific practice and public consciousness. Photographs of Earth—most famously from the Apollo missions—spawned the “overview effect,” a cognitive shift in which observers perceive the planet’s unity, beauty and apparent fragility. The subsequent expansion of Earth‑observation science and space‑based monitoring has provided systematic, global datasets that reveal environmental interconnections and the scale of anthropogenic change, thereby underpinning scientific understanding and policy‑relevant awareness.
Direct human observation from low Earth orbit continues to exemplify this interplay between perception and science: images taken from the International Space Station’s Cupola, such as those by astronaut Tracy Caldwell Dyson in 2010, illustrate how orbital vantage points both inform scientific measurement and reinforce cultural appreciations of Earth as a single, inhabited world. Together, symbolic, mythic and empirical strands trace an evolving human relationship to the planet, from localized cosmologies to a system‑level awareness that informs contemporary stewardship debates.