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The troposphere 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, [17] with some variation due
Understanding planetary habitability is partly an extrapolation of the conditions on Earth, as this is the only planet known to support life.. Planetary habitability is the measure of a planet's or a natural satellite's potential to develop and maintain an environment hospitable to life. [1]
The atmosphere present from this point in Earth's history until the origin of life is referred to as the prebiotic atmosphere. It is unknown when exactly life originated. The oldest direct evidence for life on Earth is around 3.5 billion years old, such as fossil stromatolites from North Pole, Western Australia. [14]
Lovelock called it first the Earth feedback hypothesis, [43] and it was a way to explain the fact that combinations of chemicals including oxygen and methane persist in stable concentrations in the atmosphere of the Earth. Lovelock suggested detecting such combinations in other planets' atmospheres as a relatively reliable and cheap way to ...
The composition of Earth's atmosphere is determined by the by-products of the life that it sustains. Dry air (mixture of gases) from Earth's atmosphere contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases (by volume), but generally a variable amount of water vapor is ...
The atmosphere envelops the earth and extends hundreds of kilometres from the surface. It consists mostly of inert nitrogen (78%), oxygen (21%) and argon (0.9%). [4] Some trace gases in the atmosphere, such as water vapour and carbon dioxide, are the gases most important for the workings of the climate system, as they are greenhouse gases which allow visible light from the Sun to penetrate to ...
Much Earth System science therefore relies on studies of the Earth's past behaviour and models to anticipate future behaviour in response to pressures. Life: Biological processes play a much stronger role in the functioning and responses of the Earth System than previously thought. It appears to be integral to every part of the Earth System.
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. [237]