The Earth From the Air

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Earth is the third planet from the sun, after Mercury and Venus, and before Mars. It is about 150 million kilometers (about 93 million miles) from the sun. This distance, called an astronomical unit (AU), is a standard unit of measurement in astronomy. Earth is one AU from the sun. The planet Jupiter is about 5.2 AU from the sun—about 778 million kilometers (483.5 million miles). 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 2O) absorbs at many wavelengths above 700nm. When a molecule absorbs a photon, it increases the energy of the molecule. This heats the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below. Paleontologists, geologists, and other scientists divide Earth’s history into time periods. The largest time period is the supereon, and only applies to one unit of time, the Precambrian. Eons, eras, and periods are smaller units of geologic time. The mass of the oceans is approximately 1.35 ×10 18 metric tons or about 1/4400 of Earth's total mass. The oceans cover an area of 361.8millionkm 2 (139.7millionsqmi) with a mean depth of 3,682m (12,080ft), resulting in an estimated volume of 1.332billionkm 3 (320millioncumi). [190] If all of Earth's crustal surface were at the same elevation as a smooth sphere, the depth of the resulting world ocean would be 2.7 to 2.8km (1.68 to 1.74mi). [191] About 97.5% of the water is saline; the remaining 2.5% is fresh water. [192] [193] Most fresh water, about 68.7%, is present as ice in ice caps and glaciers. [194] The remaining 30% is ground water, 1% surface water (covering only 2.8% of Earth's land) [195] and other small forms of fresh water deposits such as permafrost, water vapor in the atmosphere, biological binding, etc. . [196] [197]

Marshak, Alexander; Várnai, Tamás; Kostinski, Alexander (15 May 2017). "Terrestrial glint seen from deep space: oriented ice crystals detected from the Lagrangian point". Geophysical Research Letters. 44 (10): 5197. Bibcode: 2017GeoRL..44.5197M. doi: 10.1002/2017GL073248. S2CID 109930589. Main article: Earth's internal heat budget A map of heat flow from Earth's interior to the surface of Earth's crust, mostly along the oceanic ridges

At Earth's polar regions, the 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. J. Schopf: Earth's Earliest Biosphere: Its Origin and Evolution. Princeton University Press, Princeton, N.J., 1983 Other layers The volume fraction of the main gases in Earth's atmosphere according to height. The boundary between the homosphere (left) and heterosphere (right) is at about 100 km. The outermost layer of the exosphere (off the chart) is dominated by hydrogen. [32] 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. [165] 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. [110] [111] Earth has an estimated 16.7millionkm 2 (6.4millionsqmi) of cropland and 33.5millionkm 2 (12.9millionsqmi) of pastureland. [112]

In general, air pressure and density decrease with altitude in the atmosphere. However, the temperature has a more complicated profile with altitude, and may remain relatively constant or even increase with altitude in some regions (see the temperature section, below). 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. In this way, Earth's atmosphere can be divided (called atmospheric stratification) into five main layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. [18] The altitudes of the five layers are as follows: 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 18 kg (1.135×10 19 lb), [40] about 2.5% less than would be inferred from 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.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 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. About 78% of the atmosphere is nitrogen gas, N2, which is unreactive and just sort of hangs around. Earth’s physical environment is often described in terms of spheres: the magnetosphere, the atmosphere, the hydrosphere, and the lithosphere. Parts of these spheres make up the biosphere, the area of Earth where life exists.

Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time ( 86,400.0025 SI seconds). [153] Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 ms longer than the mean solar day. [154] [155]Main article: Axial tilt §Earth Earth's axial tilt causing different angles of seasonal illumination at different orbital positions around the Sun 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 is because clouds (H 2O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. The hydrosphere is composed of all the water on Earth. Nearly three-fourths of Earth is covered in water, most of it in the ocean. Less than three percent of the hydrosphere is made up of freshwater. Most freshwater is frozen in ice sheets and glaciers in Antarctica, the North American island of Greenland, and the Arctic. Freshwater can also be found underground, in chambers called aquifers, as well as rivers, lakes, and springs. The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe. [24] It has cognates in every Germanic language, and their ancestral root has been reconstructed as * erþō. In its earliest attestation, the word eorðe was used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ("Earth"), a giantess often given as the mother of Thor. [25] States, Robert J.; Gardner, Chester S. (January 2000). "Thermal Structure of the Mesopause Region (80–105 km) at 40°N Latitude. Part I: Seasonal Variations". Journal of the Atmospheric Sciences. 57 (1): 66–77. Bibcode: 2000JAtS...57...66S. doi: 10.1175/1520-0469(2000)057<0066:TSOTMR>2.0.CO;2.

About 3.4 billion years ago, nitrogen formed the major part of the then stable "second atmosphere". The influence of life has to be taken into account rather soon in the history of the atmosphere because hints of early life-forms appear as early as 3.5 billion years ago. [52] How Earth at that time maintained a climate warm enough for liquid water and life, if the early Sun put out 30% lower solar radiance than today, is a puzzle known as the " faint young Sun paradox". IPCC (2021). "Summary for Policymakers" (PDF). IPCC AR6 WG1. pp.4–5. Archived from the original (PDF) on 2021-08-11 . Retrieved 2021-11-20. Earth orbits the Sun, making Earth the third-closest planet to the Sun and part of the inner Solar System. Earth's average orbital distance is about 150millionkm (93millionmi), which is the basis for the Astronomical Unit and is equal to roughly 8.3 light minutes or 380 times Earth's distance to the Moon. 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 420km (220 and 260mi). It is this layer where many of the satellites orbiting the Earth are present.Main article: Internal structure of Earth Geologic layers of Earth [125] Illustration of Earth's cutaway, not to scale Within the five principal layers above, which are largely determined by temperature, several secondary layers may be distinguished by other properties: If the entire mass of the atmosphere had a uniform density equal to sea level density (about 1.2kg per m 3) from sea level upwards, it would terminate abruptly at an altitude of 8.50km (27,900ft).