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72-441: The region experiences great extremes of temperature during the year. During the winter months, the air is prone to stratification due to temperature inversions, leading to thick fogs. At the same time, a katabatic wind called the "Tanana Valley Jet" can form, blowing from the southeast to the northwest. During the summer, the surrounding plains are generally boglike, and include much permafrost and many pingos . The Tanana Valley

144-435: A boundary marked in most places by a temperature inversion (i.e. a layer of relatively warm air above a colder one), and in others by a zone that is isothermal with height. Although variations do occur, the temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth's surface)

216-505: A factor of 1/ e (0.368) every 7.64 km (25,100 ft), (this is called the scale height ) -- for altitudes out to around 70 km (43 mi; 230,000 ft). However, the atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account. At heights over 100 km, an atmosphere may no longer be well mixed. Then each chemical species has its own scale height. In summary,

288-443: A few groups are carnivorous. Carnivorous gastropods usually feed on other gastropod species or on weak individuals of the same species; some feed on insect larvae or earthworms. Semi-terrestrial animals are macroscopic animals that rely on very moist environments to thrive, they may be considered a transitional point between true terrestrial animals and aquatic animals. Among vertebrates, amphibians have this characteristic relying on

360-434: A few months, they famously can enter suspended animation during dry or hostile conditions and survive for decades, which allows them to be ubiquitous in terrestrial environments despite needing water to grow and reproduce. Many microscopic crustacean groups like copepods and amphipods and seed shrimps are known to go dormant when dry and live in transient bodies of water too. This article incorporates CC-BY-2.0 text from

432-424: A film of water to live in, and are therefore considered semi-terrestrial. Flatworms, ribbon worms, velvet worms and annelids all depend on more or less moist habitats. The three remaining phyla, arthropods, mollusks, and chordates, all contain species that have adapted totally to dry terrestrial environments, and which have no aquatic phase in their life cycles. Labeling an animal species "terrestrial" or "aquatic"

504-514: A layer in which temperatures rise with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet radiation (UV) from the Sun by the ozone layer, which restricts turbulence and mixing. Although the temperature may be −60 °C (−76 °F; 210 K) at the tropopause, the top of the stratosphere is much warmer, and may be near 0 °C. The stratospheric temperature profile creates very stable atmospheric conditions, so

576-574: A mass of about 5.15 × 10  kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space . The Kármán line , at 100 km (62 mi) or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). Several layers can be distinguished in

648-520: A mild or tropical climate during the Paleozoic and Mesozoic , whereas few animals became fully terrestrial during the Cenozoic . If internal parasites are excluded, free living species in terrestrial environments are represented by the following eleven phyla: Roundworms, gastrotrichs, tardigrades, rotifers and some smaller species of arthropods and annelids are microscopic animals that require

720-485: A million miles away, were found to be reflected light from ice crystals in the atmosphere. When light passes through Earth's atmosphere, photons interact with it through scattering . If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you cannot see your shadow, there

792-511: A moist environment and breathing through their moist skin while reproducing in water. Many other animal groups solely have terrestrial animals that live like this: land planarians , land ribbon worms , roundworms (nematodes), and land annelids (clitellates) who are very primitive and breathe through skin . Clitellates or terrestrial annelids demonstrate many unique terrestrial adaptations especially in their methods of reproduction, they tend towards being simpler than their marine relatives,

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864-561: A preferable alternative to traditional fins in extremely shallow water), and lungs which existed in conjunction with gills, Tiktaalik and animals like it were able to establish a strong foothold on land by the end of the Devonian period. In the Carboniferous , tetrapods (losing their gills) became fully terrestrialized, allowing their expansion into most terrestrial niches, though later on some will return to being aquatic and conquer

936-737: A protective buffer between the Earth's surface and outer space , shields the surface from most meteoroids and ultraviolet solar radiation , keeps it warm and reduces diurnal temperature variation (temperature extremes between day and night ) through heat retention ( greenhouse effect ), redistributes heat and moisture among different regions via air currents , and provides the chemical and climate conditions allowing life to exist and evolve on Earth. By mole fraction (i.e., by quantity of molecules ), dry air contains 78.08% nitrogen , 20.95% oxygen , 0.93% argon , 0.04% carbon dioxide , and small amounts of other trace gases . Air also contains

1008-445: A variable amount of water vapor , on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature and atmospheric pressure vary with altitude . Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and respiration of terrestrial animals is found only within 12 kilometres (7.5 mi) from the ground. Earth's early atmosphere consisted of accreted gases from

1080-557: Is 14 °C (57 °F; 287 K) or 15 °C (59 °F; 288 K), depending on the reference. The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as 101325 pascals (760.00  Torr ; 14.6959  psi ; 760.00  mmHg ). This is sometimes referred to as a unit of standard atmospheres (atm) . Total atmospheric mass is 5.1480×10 kg (1.135×10 lb), about 2.5% less than would be inferred from

1152-408: Is about 1.2 kg/m (1.2 g/L, 0.0012 g/cm ). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law ). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula . More sophisticated models are used to predict

1224-414: Is about 28.946 or 28.96  g/mol. This is decreased when the air is humid. The relative concentration of gases remains constant until about 10,000 m (33,000 ft). In general, air pressure and density decrease with altitude in the atmosphere. However, temperature has a more complicated profile with altitude and may remain relatively constant or even increase with altitude in some regions (see

1296-399: Is an early aquatic form, either a nymph or larva . There are crab species that are completely aquatic, crab species that are amphibious, and crab species that are terrestrial. Fiddler crabs are called "semi-terrestrial" since they make burrows in the muddy substrate, to which they retreat during high tides. When the tide is out, fiddler crabs search the beach for food. The same is true in

1368-442: Is because clouds (H 2 O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. The greenhouse effect is directly related to this absorption and emission effect. Some gases in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these are CO 2 and H 2 O. The refractive index of air

1440-1429: Is called paleoclimatology . The three major constituents of Earth's atmosphere are nitrogen , oxygen , and argon . Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by mole fraction in the coldest portions of the atmosphere to as much as 5% by mole fraction in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor). The remaining gases are often referred to as trace gases, among which are other greenhouse gases , principally carbon dioxide, methane, nitrous oxide, and ozone. Besides argon, other noble gases , neon , helium , krypton , and xenon are also present. Filtered air includes trace amounts of many other chemical compounds . Many substances of natural origin may be present in locally and seasonally variable small amounts as aerosols in an unfiltered air sample, including dust of mineral and organic composition, pollen and spores , sea spray , and volcanic ash . Various industrial pollutants also may be present as gases or aerosols, such as chlorine (elemental or in compounds), fluorine compounds and elemental mercury vapor. Sulfur compounds such as hydrogen sulfide and sulfur dioxide (SO 2 ) may be derived from natural sources or from industrial air pollution. Mole fraction

1512-447: Is close to, but just greater than, 1. Systematic variations in the refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers on board ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of Earth's surface. The refractive index of air depends on temperature, giving rise to refraction effects when

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1584-519: Is due to physiological, behavioral, and morphological adaptations to water availability, as well as ionic and thermal balance. They are adapted to most of the habitats on Earth. The shell of a snail is constructed of calcium carbonate , but even in acidic soils one can find various species of shell-less slugs. Land-snails, such as Xerocrassa seetzeni and Sphincterochila boissieri , also live in deserts, where they must contend with heat and aridity. Terrestrial gastropods are primarily herbivores and only

1656-785: Is in the Tanana Valley in Alaska. At the Broken Mammoth, Swan Point, Mead, and Healy Lake, Alaska sites, the oldest dates range between 12,060 BP and 11,410. These sites contain cultural remains considered ancestral to today's Alaskan Native inhabitants. The oldest stratified sites in the Nenana Valley region date to from 11,820 to 11,010 BP. The Mesa complex in northern Alaska dates to 11,660 BP." More recently, Tanana Valley sites have been dated to pre-Clovis period, or 13,000–14,000 cal yr BP. The Broken Mammoth site,

1728-477: Is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase. The atoms and molecules are so far apart that they can travel hundreds of kilometres without colliding with one another. Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space . These free-moving particles follow ballistic trajectories and may migrate in and out of

1800-445: Is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering , shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal before reaching your eye. Much of

1872-457: Is often obscure and becomes a matter of judgment. Many animals considered terrestrial have a life-cycle that is partly dependent on being in water. Penguins , seals , and walruses sleep on land and feed in the ocean, yet they are all considered terrestrial. Many insects, e.g. mosquitos , and all terrestrial crabs , as well as other clades, have an aquatic life cycle stage: their eggs need to be laid in and to hatch in water; after hatching, there

1944-718: Is one of the few groups that have evolved fully terrestrial taxa during the late Cenozoic in the Japanese Archipelago only. Shifts from aquatic to terrestrial life occurred at least twice within two Japanese endemic lineages in Japanese Pomatiopsidae and it started in the Late Miocene . About one-third of gastropod species are terrestrial. In terrestrial habitats they are subjected to daily and seasonal variation in temperature and water availability. Their success in colonizing different habitats

2016-562: Is one of the most important events in the history of life . Terrestrial lineages evolved in several animal phyla , among which arthropods, vertebrates and mollusks are representatives of more successful groups of terrestrial animals. Terrestrial animals do not form a unified clade ; rather, they are a polyphyletic group that share only the fact that they live on land. The transition from an aquatic to terrestrial life by various groups of animals has occurred independently and successfully many times. Most terrestrial lineages originated under

2088-513: Is so tenuous that some scientists consider it to be part of interplanetary space rather than part of the atmosphere). It extends from the thermopause (also known as the "exobase") at the top of the thermosphere to a poorly defined boundary with the solar wind and interplanetary medium . The altitude of the exobase varies from about 500 kilometres (310 mi; 1,600,000 ft) to about 1,000 kilometres (620 mi) in times of higher incoming solar radiation. The upper limit varies depending on

2160-481: Is sometimes referred to as volume fraction ; these are identical for an ideal gas only. ppm: parts per million by molecular count The concentration of CO 2 has been increasing in recent decades , as has that of CH 4 . Water vapor is about 0.25% by mass over full atmosphere Water vapor varies significantly locally The average molecular weight of dry air, which can be used to calculate densities or to convert between mole fraction and mass fraction,

2232-461: Is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km (7.5 mi; 39,000 ft), although this altitude varies from about 9 km (5.6 mi; 30,000 ft) at the geographic poles to 17 km (11 mi; 56,000 ft) at the Equator , with some variation due to weather. The troposphere is bounded above by the tropopause ,

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2304-540: Is the most populated area of Alaska north of the Alaska Range. Its largest city is Fairbanks . Other communities include: According to James Q. Jacobs, Tanana Valley has the earliest evidence of human occupation in Alaska. "At least three distinct lithic complexes appear in the Alaskan archaeological record at approximately the same time, between 12,060 and 11,660 B.P. The earliest firm evidence of human occupation

2376-412: Is too low to conduct a significant amount of energy to or from the skin. This layer is completely cloudless and free of water vapor. However, non-hydrometeorological phenomena such as the aurora borealis and aurora australis are occasionally seen in the thermosphere. The International Space Station orbits in this layer, between 350 and 420 km (220 and 260 mi). It is this layer where many of

2448-479: Is typically the warmest section of the troposphere. This promotes vertical mixing (hence, the origin of its name in the Greek word τρόπος, tropos , meaning "turn"). The troposphere contains roughly 80% of the mass of Earth's atmosphere. The troposphere is denser than all its overlying layers because a larger atmospheric weight sits on top of the troposphere and causes it to be most severely compressed. Fifty percent of

2520-468: Is used to describe animals that live on the ground, as opposed to arboreal animals that live in trees. The term "terrestrial" is typically applied to species that live primarily on or in the ground, in contrast to arboreal species, who live primarily in trees, even though the latter are actually a specialized subgroup of the terrestrial fauna. There are other less common terms that apply to specific subgroups of terrestrial animals: Terrestrial invasion

2592-489: The Early Devonian . Among arthropods, many microscopic crustacean groups like copepods and amphipods and seed shrimp can go dormant when dry and live in transient bodies of water. By approximately 375 million years ago the bony fish best adapted to life in shallow coastal/swampy waters (such as Tiktaalik roseae ). Thanks to relatively strong, muscular limbs (which were likely weight-bearing, thus making them

2664-582: The F-layer of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months, otherwise, orbital decay will occur resulting in a return to Earth. Depending on solar activity, satellites can experience noticeable atmospheric drag at altitudes as high as 700–800 km. The division of the atmosphere into layers mostly by reference to temperature is discussed above. Temperature decreases with altitude starting at sea level, but variations in this trend begin above 11 km, where

2736-613: The Paleozoic or Mesozoic . Gastropods are especially unique due to several fully terrestrial and epifaunal lineages that evolved during the Cenozoic . Some members of rissooidean families Truncatellidae , Assimineidae , and Pomatiopsidae are considered to have colonized to land during the Cenozoic. Most truncatellid and assimineid snails amphibiously live in intertidal and supratidal zones from brackish water to pelagic areas. Terrestrial lineages likely evolved from such ancestors. The rissooidean gastropod family Pomatiopsidae

2808-935: The Swan Point Archaeological Site , and the Mead Archaeological Site are the earliest dated sites in Alaska. They are located along the Tanana River. 64°24′N 147°00′W  /  64.4°N 147.0°W  / 64.4; -147.0 Atmospheric stratification The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth 's planetary surface (both lands and oceans ), known collectively as air , with variable quantities of suspended aerosols and particulates (which create weather features such as clouds and hazes ), all retained by Earth's gravity . The atmosphere serves as

2880-750: The bristleworms , lacking many of the complex appendages the latter have. Velvet worms are prone to desiccation not due to breathing through their skin but due to their spiracles being inefficient at protecting from desiccation, like clitellates they demonstrate extensive terrestrial adaptations and differences from their marine relatives including live birth. Many animals live in terrestrial environments by thriving in transient often microscopic bodies of water and moisture, these include rotifers and gastrotrichs which lay resilient eggs capable of surviving years in dry environments, and some of which can go dormant themselves. Nematodes are usually microscopic with this lifestyle. Although eutardigrades only have lifespans of

2952-588: The infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, the radio window runs from about one centimetre to about eleven-metre waves. Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their " black body " emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example,

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3024-433: The magnetosphere or the solar wind. Every second, the Earth loses about 3 kg of hydrogen, 50 g of helium, and much smaller amounts of other constituents. The exosphere is too far above Earth for meteorological phenomena to be possible. However, Earth's auroras —the aurora borealis (northern lights) and aurora australis (southern lights)—sometimes occur in the lower part of the exosphere, where they overlap into

3096-402: The mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth and has an average temperature around −85  °C (−120  °F ; 190  K ). Just below the mesopause, the air is so cold that even the very scarce water vapor at this altitude can condense into polar-mesospheric noctilucent clouds of ice particles. These are the highest clouds in

3168-577: The mollusca . Many hundreds of gastropod genera and species live in intermediate situations, such as for example, Truncatella . Some gastropods with gills live on land, and others with a lung live in the water. As well as the purely terrestrial and the purely aquatic animals, there are many borderline species. There are no universally accepted criteria for deciding how to label these species, thus some assignments are disputed. Fossil evidence has shown that sea creatures, likely arthropods, first began to make forays onto land around 530 million years ago, in

3240-451: The solar nebula , but the atmosphere changed significantly over time, affected by many factors such as volcanism , impact events , weathering and the evolution of life (particularly the photoautotrophs ). Recently, human activity has also contributed to atmospheric changes , such as climate change (mainly through deforestation and fossil fuel -related global warming ), ozone depletion and acid deposition . The atmosphere has

3312-428: The temperature section). Because the general pattern of the temperature/altitude profile, or lapse rate , is constant and measurable by means of instrumented balloon soundings , the temperature behavior provides a useful metric to distinguish atmospheric layers. This atmospheric stratification divides the Earth's atmosphere into five main layers: The exosphere is the outermost layer of Earth's atmosphere (though it

3384-511: The tropopause . This layer extends from the top of the troposphere at roughly 12 km (7.5 mi; 39,000 ft) above Earth's surface to the stratopause at an altitude of about 50 to 55 km (31 to 34 mi; 164,000 to 180,000 ft). The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level . It contains the ozone layer , which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines

3456-573: The Early Cambrian . There is little reason to believe, however, that animals first began living reliably on land around that time. A more likely hypothesis is that these early arthropods' motivation for venturing onto dry land was to mate (as modern horseshoe crabs do) or to lay eggs out of the reach of predators. Three groups of arthropods had independently adapted to land by the end of the Cambrian: myriapods , hexapods and arachnids . By

3528-573: The Kármán line, significant atmospheric effects such as auroras still occur. Meteors begin to glow in this region, though the larger ones may not burn up until they penetrate more deeply. The various layers of Earth's ionosphere , important to HF radio propagation, begin below 100 km and extend beyond 500 km. By comparison, the International Space Station and Space Shuttle typically orbit at 350–400 km, within

3600-459: The Sun is approximately 6,000  K (5,730  °C ; 10,340  °F ), its radiation peaks near 500 nm, and is visible to the human eye. Earth is approximately 290 K (17 °C; 62 °F), so its radiation peaks near 10,000 nm, and is much too long to be visible to humans. Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights Earth's surface cools down faster than on cloudy nights. This

3672-701: The air also. Gastropod mollusks are one of the most successful animals that have diversified in the fully terrestrial habitat. They have evolved terrestrial taxa in more than nine lineages. They are commonly referred to as land snails and slugs . Terrestrial invasion of gastropod mollusks has occurred in Neritopsina , Cyclophoroidea , Littorinoidea , Rissooidea , Ellobioidea , Onchidioidea , Veronicelloidea , Succineoidea , and Stylommatophora , and in particular, each of Neritopsina, Rissooidea and Ellobioidea has likely achieved land invasion more than once. Most terrestrialization events have occurred during

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3744-420: The aptly-named thermosphere above 90 km. Because in an ideal gas of constant composition the speed of sound depends only on temperature and not on pressure or density, the speed of sound in the atmosphere with altitude takes on the form of the complicated temperature profile (see illustration to the right), and does not mirror altitudinal changes in density or pressure. The density of air at sea level

3816-421: The atmosphere also cools by emitting radiation, as discussed below. The combined absorption spectra of the gases in the atmosphere leave "windows" of low opacity , allowing the transmission of only certain bands of light. The optical window runs from around 300 nm ( ultraviolet -C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400–700 nm and continues to

3888-399: The atmosphere and may be visible to the naked eye if sunlight reflects off them about an hour or two after sunset or similarly before sunrise. They are most readily visible when the Sun is around 4 to 16 degrees below the horizon. Lightning-induced discharges known as transient luminous events (TLEs) occasionally form in the mesosphere above tropospheric thunderclouds . The mesosphere is also

3960-489: The atmosphere based on characteristics such as temperature and composition, namely the troposphere , stratosphere , mesosphere , thermosphere (formally the ionosphere ) and exosphere . The study of Earth's atmosphere and its processes is called atmospheric science (aerology), and includes multiple subfields, such as climatology and atmospheric physics . Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann . The study of historic atmosphere

4032-637: The average sea level pressure and Earth's area of 51007.2 megahectares, this portion being displaced by Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather . If the entire mass of the atmosphere had a uniform density equal to sea level density (about 1.2 kg per m ) from sea level upwards, it would terminate abruptly at an altitude of 8.50 km (27,900 ft). Air pressure actually decreases exponentially with altitude, dropping by half every 5.6 km (18,000 ft) or by

4104-414: The blue light has been scattered out, leaving the red light in a sunset. Different molecules absorb different wavelengths of radiation. For example, O 2 and O 3 absorb almost all radiation with wavelengths shorter than 300 nanometres . Water (H 2 O) absorbs at many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. This heats the atmosphere, but

4176-415: The definition. Various authorities consider it to end at about 10,000 kilometres (6,200 mi) or about 190,000 kilometres (120,000 mi)—about halfway to the moon, where the influence of Earth's gravity is about the same as radiation pressure from sunlight. The geocorona visible in the far ultraviolet (caused by neutral hydrogen) extends to at least 100,000 kilometres (62,000 mi). This layer

4248-434: The gas molecules are so far apart that its temperature in the usual sense is not very meaningful. The air is so rarefied that an individual molecule (of oxygen , for example) travels an average of 1 kilometre (0.62 mi; 3300 ft) between collisions with other molecules. Although the thermosphere has a high proportion of molecules with high energy, it would not feel hot to a human in direct contact, because its density

4320-510: The late Ordovician , they may have fully terrestrialized. There are other groups of arthropods, all from malacostracan crustaceans, which independently became terrestrial at a later date: woodlice , sandhoppers , and terrestrial crabs . Additionally, the sister panarthropodan groups Onychophora (velvet worms) are also terrestrial, while the Eutardigrada are also adapted for land to some degree; both groups probably becoming so during

4392-403: The layer where most meteors burn up upon atmospheric entrance. It is too high above Earth to be accessible to jet-powered aircraft and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft . The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by

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4464-482: The mass of Earth's atmosphere is distributed approximately as follows: By comparison, the summit of Mount Everest is at 8,848 m (29,029 ft); commercial airliners typically cruise between 10 and 13 km (33,000 and 43,000 ft) where the lower density and temperature of the air improve fuel economy; weather balloons reach 30.4 km (100,000 ft) and above; and the highest X-15 flight in 1963 reached 108.0 km (354,300 ft). Even above

4536-514: The orbital decay of satellites. The average mass of the atmosphere is about 5 quadrillion (5 × 10 ) tonnes or 1/1,200,000 the mass of Earth. According to the American National Center for Atmospheric Research , "The total mean mass of the atmosphere is 5.1480 × 10  kg with an annual range due to water vapor of 1.2 or 1.5 × 10  kg, depending on whether surface pressure or water vapor data are used; somewhat smaller than

4608-526: The previous estimate. The mean mass of water vapor is estimated as 1.27 × 10  kg and the dry air mass as 5.1352 ±0.0003 × 10  kg." Solar radiation (or sunlight) is the energy Earth receives from the Sun . Earth also emits radiation back into space, but at longer wavelengths that humans cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere. In May 2017, glints of light, seen as twinkling from an orbiting satellite

4680-422: The satellites orbiting the Earth are present. The mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about 50 km (31 mi; 160,000 ft) to the mesopause at 80–85 km (50–53 mi; 260,000–280,000 ft) above sea level. Temperatures drop with increasing altitude to

4752-447: The stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft . The troposphere

4824-773: The temperature gradient is large. An example of such effects is the mirage . Terrestrial animal Terrestrial animals are animals that live predominantly or entirely on land (e.g. cats , chickens , ants , most spiders ), as compared with aquatic animals , which live predominantly or entirely in the water (e.g. fish , lobsters , octopuses ), and semiaquatic animals, which rely on both aquatic and terrestrial habitats (e.g. platypus , most amphibians ). Some groups of insects are terrestrial , such as ants , butterflies , earwigs , cockroaches , grasshoppers and many others, while other groups are partially aquatic, such as mosquitoes and dragonflies , which pass their larval stages in water. Alternatively, terrestrial

4896-444: The temperature stabilizes over a large vertical distance through the rest of the troposphere. In the stratosphere , starting above about 20 km, the temperature increases with height, due to heating within the ozone layer caused by the capture of significant ultraviolet radiation from the Sun by the dioxygen and ozone gas in this region. Still another region of increasing temperature with altitude occurs at very high altitudes, in

4968-442: The thermopause varies considerably due to changes in solar activity. Because the thermopause lies at the lower boundary of the exosphere, it is also referred to as the exobase . The lower part of the thermosphere, from 80 to 550 kilometres (50 to 342 mi) above Earth's surface, contains the ionosphere . The temperature of the thermosphere gradually increases with height and can rise as high as 1500 °C (2700 °F), though

5040-429: The thermosphere. The exosphere contains many of the artificial satellites that orbit Earth. The thermosphere is the second-highest layer of Earth's atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80 km (50 mi; 260,000 ft) up to the thermopause at an altitude range of 500–1000 km (310–620 mi; 1,600,000–3,300,000 ft). The height of

5112-419: The total mass of the atmosphere is located in the lower 5.6 km (3.5 mi; 18,000 ft) of the troposphere. Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth's weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation, although very tall cumulonimbus thunder clouds can penetrate

5184-430: The tropopause from below and rise into the lower part of the stratosphere. Most conventional aviation activity takes place in the troposphere, and it is the only layer accessible by propeller-driven aircraft . Within the five principal layers above, which are largely determined by temperature, several secondary layers may be distinguished by other properties: The average temperature of the atmosphere at Earth's surface

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