Earth
 | |||||||||||||
aj) | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Average orbital speed | 29.7827 km/s[3] (107218 km/h; 66622 mph) | ||||||||||||
| 358.617° | |||||||||||||
| Inclination |
| ||||||||||||
| −11.26064°[3] to J2000 ecliptic | |||||||||||||
| 2023-Jan-04[5] | |||||||||||||
| 114.20783°[3] | |||||||||||||
| Satellites | 1, the Moon | ||||||||||||
| Physical characteristics | |||||||||||||
Mean radius | 6371.0 km (3958.8 mi)[6] | ||||||||||||
Equatorial radius | 6378.137 km (3963.191 mi)[7][8] | ||||||||||||
Polar radius | 6356.752 km (3949.903 mi)[9] | ||||||||||||
| Flattening | 1/298.257222101 (ETRS89)[10] | ||||||||||||
| Circumference |
| ||||||||||||
| Total: 510072000 km2 (196940000 sq mi)[12][n 4] Land: 148940000 km2 Sidereal rotation period | |||||||||||||
Equatorial rotation velocity | 0.4651 km/s[17] (1674.4 km/h; 1040.4 mph) | ||||||||||||
| 23.4392811°[2] | |||||||||||||
| Albedo | |||||||||||||
| Temperature | 287.91 K (14.76 °C; 58.57 °F) (blackbody temperature)[18] | ||||||||||||
| |||||||||||||
| Surface equivalent dose rate | 0.274 μSv/h[22] | ||||||||||||
| Atmosphere | |||||||||||||
Surface pressure | 101.325 kPa (at sea level) | ||||||||||||
| Composition by volume | |||||||||||||
Earth is the third
Earth is
Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas in the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago, and reached a population of 8 billion on November 15, 2022. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.[24]
Etymology
The
Historically, earth has been written in lowercase. From
Occasionally, the name Terra
There are a number of adjectives for the planet Earth. From Earth itself comes earthly. From the Latin Terra comes terran /ˈtɛrən/,[31] terrestrial /təˈrɛstriəl/,[32] and (via French) terrene /təˈriːn/,[33] and from the Latin Tellus comes tellurian /tɛˈlʊəriən/[34] and telluric.[35]
Natural history
Formation
The oldest material found in the Solar System is dated to 4.5682+0.0002
−0.0004
Estimates of the age of the Moon range from 4.5 Ga to significantly younger.
After formation
Earth's atmosphere and oceans were formed by volcanic activity and outgassing.[45] Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets.[46] Sufficient water to fill the oceans may have been on Earth since it formed.[47] In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity.[48] By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.[49]
As the molten outer layer of Earth cooled it
New continental crust forms as a result of plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma, one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia at 600–540 Ma, then finally Pangaea, which also began to break apart at 180 Ma.[57]
The most recent pattern of
Origin of life and evolution
During the
Future
.Due to Earth's rotation it has the shape of an ellipsoid, bulging at its Equator, reaching 43 kilometers (27 mi) further out from its center of mass than at its poles.[86][87] Earth's shape furthermore has local
Parallel to the rigid land topography the Ocean exhibits a more dynamic topography.[93]To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a shape called a geoid. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but gravitational irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements.[94]
Surface
 | This section may require , showing vegetation, clouds and bodies of water
Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, Earth's shape is an idealized spheroid - a squashed sphere - with a surface area of about 510 million km2 (197 million sq mi).[12] Earth can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres. Most of Earth's surface is ocean water: 70.8% or 361 million km2 (139 million sq mi).[95] This vast pool of salty water is often called the world ocean,[96][97] and makes Earth with its dynamic hydrosphere a water world[98][99] or ocean world.[100][101] Indeed, in Earth's early history the ocean may have covered Earth completely.[102] The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean, from largest to smallest. The ocean fills the oceanic basins, and the ocean floor comprises abyssal plains, continental shelves, seamounts, submarine volcanoes,[86] oceanic trenches, submarine canyons, oceanic plateaus, and a globe-spanning mid-ocean ridge system. At Earth's ocean surface is covered by seasonally variable amounts of sea ice that often connects with polar land, permafrost and ice sheets, forming polar ice caps .
Earth's land covers 29.2%, or 149 million km2 (58 million sq mi) of Earth's surface. The land surface includes many islands around the globe, but most of the land surface is taken by the four continental landmasses, which are (in descending order): Africa-Eurasia, America (landmass), Antarctica, and Australia (landmass).[103][104][105] These landmasses are further broken down and grouped into the continents. The terrain of the land surface varies greatly and consists of mountains, deserts, plains, plateaus, and other landforms. The elevation of the land surface varies from a low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft).[106] Land can be covered by surface water, snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation,[107] but ice sheets (10%,[108] not including the equally large land under permafrost)[109] or cold as well as hot deserts (33%)[110] occupy also considerable amounts of it. The pedosphere is the outermost layer of Earth's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Earth's total arable land is 10.7% of the land surface, with 1.3% being permanent cropland.[111][112] Earth has an estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.[113] The land surface and the ocean floor form the top of the Earth's crust, which together with parts of the upper mantle form Earth's lithosphere. Earth's crust may be divided into oceanic and continental crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly basaltic, while the continental crust may include lower density materials such as granite, sediments and metamorphic rocks.[114]  .Earth's surface ocean water .
Erosion and tectonics, volcanic eruptions, flooding, weathering, glaciation, and the growth and decomposition of biomass into soil are among the processes that constantly reshape Earth's crust over geological time.[115][116] Sedimentary rock is formed from the accumulation of sediment that becomes buried and compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust.[117] Tectonic platesEarth's mechanically rigid outer layer of Earth's crust and upper mantle, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: at convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur.[119] The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates.[120] As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old.[121][122] By comparison, the oldest dated continental crust is 4,030 Ma,[123] although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to 4,400 Ma, indicating that at least some continental crust existed at that time.[51] The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include 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 Australian Plate fused with the Indian Plate between 50 and 55 Ma. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year)[124] and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of 10.6 mm/a (0.42 in/year).[125] Internal structure
Earth's interior, like that of the other terrestrial planets, is divided into layers by their upper mantle are collectively known as the lithosphere, which is divided into independently moving tectonic plates.[129]
Beneath the lithosphere is the outer core lies above a solid inner core.[130] Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed.[131] The radius of the inner core is about one-fifth of that of Earth.
Density increases with depth, as described in the table on the right.
Among the Solar System's planetary-sized objects Earth is the object with the highest density .
Chemical compositionaluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation, the core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.[132][50] The most common rock constituents of the crust are oxides. Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals), aluminum, iron, calcium, magnesium, potassium, or sodium.[133][132]
Internal heatoceanic ridges The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232.[134] At the center, the temperature may be up to 6,000 °C (10,830 °F),[135] and the pressure could reach 360 GPa (52 million psi).[136] Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.[137][138] The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42×1013 W.[139] 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. These plumes can produce hotspots and flood basalts.[140] More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans because the crust there is much thinner than that of the continents.[141] Gravitational fieldThe gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration is approximately 9.8 m/s2 (32 ft/s2). Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as gravity anomalies.[142] Magnetic field Schematic of Earth's magnetosphere, with the solar wind flows from left to rightThe main part of Earth's magnetic field is generated in the core, the site of a magnetic dipole moment of 7.79×1022 Am2 at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average).[143] The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.[144][145]
The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail.[146] Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the dayside magnetosphere within the solar wind.[147] Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates.[148][149] The ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field,[150] and the Van Allen radiation belts are formed by high-energy particles whose motion is essentially random, but contained in the magnetosphere.[151][152] During aurora.[153]
Orbit and rotationRotation Earth's rotation imaged by Deep Space Climate Observatory , showing axis tiltEarth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 Earth's rotation period relative to the precessing or moving mean March equinox (when the Sun is at 90° on the equator), is 86,164.0905 seconds of mean solar time (UT1) (23h 56m 4.0905s).[2] Thus the sidereal day is shorter than the stellar day by about 8.4 ms.[157]
Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.[158][159] OrbitEarth orbits the Sun, making Earth the third-closest planet to the Sun and part of the light minutes or 380 times Earth's distance to the Moon .
Earth orbits the Sun every 365.2564 mean solar days, or one sidereal year. With an apparent movement of the Sun in Earth's sky at a rate of about 1°/day eastward, which is one apparent Sun or Moon diameter every 12 hours. Due to 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 .
The orbital speed of Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance to the Moon, 384,000 km (239,000 mi), in about 3.5 hours.[3] The Moon and Earth orbit a common counterclockwise. Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth-Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.[3][160]
The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius.[161][n 10] This is the maximum distance at which Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.[161] Earth, along with the Solar System, is situated in the Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm.[162] Axial tilt and seasonsThe axial tilt of Earth is approximately 23.439281° By astronomical convention, the four seasons can be determined by the solstices—the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped.[166] The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years.[167] The orientation (rather than the angle) of 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. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation.[168] In modern times, Earth's aphelion around 4 July. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth–Sun distance causes an increase of about 6.8% in solar energy reaching Earth at perihelion relative to aphelion.[169][n 11] Because the Southern Hemisphere is tilted toward the Sun at about the same time that 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. 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.[170]
Earth–Moon systemMoonThe Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of the Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto.[171][172] The natural satellites of other planets are also referred to as "moons", after Earth's.[173] The most widely accepted theory of the Moon's origin, the giant-impact hypothesis, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. 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 Earth's crust.[41] The gravitational attraction between Earth and the Moon causes tides on Earth.[174] 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 Earth. As a result, it always presents the same face to the planet.[175] As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases.[176] Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm/a (1.5 in/year). Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs/yr—add up to significant changes.[177] During the Ediacaran period, for example, (approximately 620 Ma) there were 400±7 days in a year, with each day lasting 21.9±0.4 hours.[178] 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.[179] Some theorists think that without this stabilization against the torques applied by the Sun and planets to Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting large changes over millions of years, as is the case for Mars, though this is disputed.[180][181] Viewed from Earth, the Moon is just far enough away to have almost 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.[159] This allows total and annular solar eclipses to occur on Earth.[182]
Asteroids and artificial satellitesEarth's near-Earth asteroid 2006 RH120 makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.[186]
As of September 2021[update], there are 4,550 operational, human-made satellites orbiting Earth.[187] There are also inoperative satellites, including Vanguard 1, the oldest satellite currently in orbit, and over 16,000 pieces of tracked space debris.[n 12] Earth's largest artificial satellite is the International Space Station.[188] Hydrosphereglobal ocean and cloud cover, which dominate Earth's surface and hydrosphere. At Earth's polar regions Earth's hydrosphere forms larger areas of ice cover.Earth's hydrosphere is the sum of Earth's water and its distribution. Most of Earth's hydrosphere consists of Earth's global ground water, 1% surface water (covering only 2.8% of Earth's land)[194] and other small forms of fresh water deposits such as permafrost, water vapor in the atmosphere, biological binding, etc. .[195][196]
In Earth's coldest regions, snow survives over the summer and ice sheets form over land in polar regions. The flow of glaciers erodes the surface changing it dramatically, with the formation of U-shaped valleys and other landforms.[197] Sea ice in the Arctic covers an area about as big as the United States, although it is quickly retreating as a consequence of climate change.[198]
The average heat reservoir.[202] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño–Southern Oscillation.[203]
The abundance of water, particularly liquid water, on Earth's surface is a unique feature that distinguishes it from other planets in the Solar System. Solar System planets with considerable atmospheres do partly host atmospheric water vapor, but they lack surface conditions for stable surface water.[204] Despite some moons showing signs of large reservoirs of extraterrestrial liquid water, with possibly even more volume than Earth's ocean, all of them are large bodies of water under a kilometers thick frozen surface layer.[205] Atmospherestratospheric blue sky at the horizon, and above this a line of green airglow of the lower thermosphere around an altitude of 100 km, at the edge of space .The atmospheric pressure at Earth's sea level averages 101.325 kPa (14.696 psi),[206] with a scale height of about 8.5 km (5.3 mi).[3] A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules.[206] Water vapor content varies between 0.01% and 4%[206] but averages about 1%.[3] Clouds cover around two thirds of Earth's surface, more so over oceans than land.[207] The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.[208] Earth's solar radiation, permitting life on land.[209] Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[210] This last phenomenon is the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the surface, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C (0 °F), in contrast to the current +15 °C (59 °F),[211] and life on Earth probably would not exist in its current form.[212]
Weather and climateEastern Pacific and the  Worldwide Köppen climate classifications Earth's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space.[213] Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface; this lowest layer is called the troposphere.[214] 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 thermal energy.[215] 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°.[216] Ocean heat content and currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.[217] Earth receives 1361 W/m2 of polar climates.[221]
Further factors that affect a location's climates are its Washington DC are both coastal cities at about the same latitude. San Francisco's climate is significantly more moderate as the prevailing wind direction is from sea to land.[224] Finally, temperatures decrease with height causing mountainous areas to be colder than low-lying areas.[225]
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 falls to the surface as precipitation.[215] Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. 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. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region.[226] The commonly used Upper atmosphere Earth's atmosphere as it appears from space, as bands of different colours at the horizon. From the bottom, afterglow illuminates the troposphere in orange with silhouettes of clouds, and the stratosphere in white and blue. Next the mesosphere (pink area) extends to just below the edge of space at one hundred kilometers and the pink line of airglow of the lower thermosphere (invisible), which hosts green and red aurorae over several hundred kilometers.The upper atmosphere, the atmosphere above the troposphere,[230] is usually divided into the stratosphere, mesosphere, and thermosphere.[210] Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind.[231] Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km (62 mi) above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.[232] Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases.[233] The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.[234] Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth.[235] In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.[236] Life on Earthocean surface (low in purple; high in yellow)Earth is the only known place that has ever been habitable for life. Earth's life developed in Earth's early bodies of water some hundred million years after Earth formed. Earth's life has been shaping and inhabiting many particular Great oxidation event .
Earth's life has over time greatly diversified, allowing the biosphere to have different water depths, planetary temperature latitudes and on land also with different humidity. Earth's species diversity and biomass reaches a peak in shallow waters and with forests, particularly in equatorial, warm and humid conditions. While freezing polar regions and high altitudes, or extremely arid areas are relatively barren of plant and animal life.[239]
Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain a metabolism.[240] Plants and other organisms take up nutrients from water, soils and the atmosphere. These nutrients are constantly recycled between different species.[241] Extreme weather, such as global warming.[245] This is driving changes such as the melting of glaciers and ice sheets, a global rise in average sea levels, increased risk of drought and wildfires, and migration of species to colder areas.[246]
Human geography A composite image of artificial light emissions at night on a map of EarthOriginating from earlier eastern Africa 300,000 years ago humans have since been migrating and with the advent of agriculture in the 10th millennium BC increasingly settling Earth's land. In the 20th century Antarctica had been the last continent to see a first and until today limited human presence.
Human population has since the 19th century grown exponentially to seven billion in the early 2010s,[247] and is projected to peak at around ten billion in the second half of the 21st century.[248] Most of the growth is expected to take place in sub-Saharan Africa.[248] Distribution and hemispherical predominance of the world's land mass, with 68% of the world's land mass being in the Northern Hemisphere.[250] Furthermore, since the 19th century humans have increasingly converged into urban areas with the majority living in urban areas by the 21st century.[251]
Beyond Earth's surface humans have lived on a temporary basis, with only special purpose deep underwater presence, and a few space stations. Human population virtually completely remains on Earth's surface, fully depending on Earth and the environment it sustains. Humans have gone and temporarily stayed beyond Earth with some hundreds of people, since the latter half of the 20th century, and only a fraction of them reaching another celestial body, the Moon.[252][253]
Earth has been subject to extensive human settlement, and humans have developed diverse over the ocean and Antarctica , and therefore all of Earth.
Natural resources and land useEarth has resources that have been exploited by humans.[257] Those termed non-renewable resources, such as fossil fuels, are only replenished over geological timescales.[258] Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal, petroleum, and natural gas.[259] These deposits are used by humans both for energy production and as feedstock for chemical production.[260] Mineral ore bodies have also been formed within the crust through a process of ore genesis, resulting from actions of magmatism, erosion, and plate tectonics.[261] These metals and other elements are extracted by mining, a process which often brings environmental and health damage.[262] Earth's biosphere produces many useful biological products for humans, including food, pharmaceuticals, oxygen, and the recycling of organic waste. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends on dissolved nutrients washed down from the land.[263] In 2019, 39 million km2 (15 million sq mi) of Earth's land surface consisted of forest and woodlands, 12 million km2 (4.6 million sq mi) was shrub and grassland, 40 million km2 (15 million sq mi) were used for animal feed production and grazing, and 11 million km2 (4.2 million sq mi) were cultivated as croplands.[264] Of the 12–14% of ice-free land that is used for croplands, 2 percentage points were irrigated in 2015.[265] Humans use building materials to construct shelters.[266]
Humans and the environment Change in average surface air temperature and drivers for that change. Human activity has caused increased temperatures, with natural forces adding some variability.[267] Human activities have impacted Earth's environments. Through activities such as the burning of fossil fuels, humans have been increasing the amount of global warming, has contributed to the melting of glaciers, rising sea levels, increased risk of drought and wildfires, and migration of species to colder areas.[246]
The concept of planetary boundaries was introduced to quantify humanity's impact on Earth. Of the nine identified boundaries, five have been crossed: Biosphere integrity, climate change, chemical pollution, destruction of wild habitats and the nitrogen cycle are thought to have passed the safe threshold.[270][271] As of 2018, no country meets the basic needs of its population without transgressing planetary boundaries. It is thought possible to provide all basic physical needs globally within sustainable levels of resource use.[272] Cultural and historical viewpoint observing the Earth below . Earth is sometimes fertility deity.[275] Creation myths in many religions involve the creation of Earth by a supernatural deity or deities.[275] The Gaia hypothesis, developed in the mid-20th century, compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability.[276][277] [278]Images of Earth taken from space, particularly during the Apollo program, have been credited with altering the way that people viewed the planet that they lived on, called the overview effect, emphasizing its beauty, uniqueness and apparent fragility.[279][280] In particular, this caused a realization of the scope of effects from human activity on Earth's environment. Enabled by science, particularly Earth observation,[281] humans have started to take action on environmental issues globally,[282] acknowledging the impact of humans and the interconnectedness of Earth's environments. Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a flat Earth was gradually displaced in Ancient Greece by the idea of a spherical Earth, which was attributed to both the philosophers Pythagoras and Parmenides.[283][284] Earth was generally believed to be the center of the universe until the 16th century, when scientists first concluded that it was a moving object, one of the planets of the Solar System.[285] It was only during the 19th century that geologists realized Lord Kelvin used thermodynamics to estimate the age of Earth to be between 20 million and 400 million years in 1864, sparking a vigorous debate on the subject; it was only when radioactivity and radioactive dating were discovered in the late 19th and early 20th centuries that a reliable mechanism for determining Earth's age was established, proving the planet to be billions of years old.[287][288]
See also
Notes
References
Cite error: A list-defined reference named "de_pater_lissauer2010" is not used in the content (see the help page). External links
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
.svg){kind=link}
