You won't find anything like the Earth’s atmosphere among the other planets of the solar system. It harbors life by protecting the Earth’s surface from ultraviolet light in solar radiation and maintains it at a global average temperature of around 15 degrees Celsius (59 degrees Fahrenheit), but the exosphere temperature can exceed 2000 degrees Celsius. The bulk composition of the atmosphere is mostly nitrogen and oxygen up to a height of between 80 to 90 kilometers (50 to 56 miles) above the Earth’s surface. The atmosphere has five distinct layers.
The Troposphere Layer
The troposphere extends from the Earth’s surface to a height of between 6 and 20 kilometers (4 and 12 miles). It is thicker at the equator, between 18 and 20 kilometers (11 and 12 miles). At the poles the atmospheric thickness is about 6 kilometers (4 miles). Global average temperature range in the troposphere decreases from 15 degrees Celsius (59 degrees Fahrenheit) on the surface to negative 51 degrees Celsius (negative 60 degrees Fahrenheit) at the top of the troposphere. Nitrogen forms 78 percent of the troposphere’s chemical composition today; oxygen, 21 percent; argon, 0.9 percent; water vapor, between 0.3 and 4 percent; and carbon dioxide. 0.04 percent. Weather, as it is recognized on Earth, happens in the troposphere.
The Protective Stratosphere
The stratosphere lies above the troposphere and extends to 50 kilometers (31 miles) above the Earth’s surface. It holds 85 percent to 90 percent of atmospheric ozone created by the photolysis – the decomposition by solar radiation – of oxygen. Ozone absorbs ultraviolet light from solar radiation and causes a temperature inversion -- where temperatures increase rather than decrease with height -- from about negative 51 degrees Celsius (negative 60 degrees Fahrenheit) at the bottom to negative 15 degrees Celsius (5 degrees Fahrenheit) at the top. Other gases include nitrous oxide, methane and chlorofluorocarbons that come from the troposphere. Volcanic eruptions on Earth directly inject sulfide compounds, halogen gases such as hydrogen chloride and fluoride, and particles of inorganic silicate and sulfate compounds into the stratosphere.
The Frigid Mesosphere
The mesosphere lies over the stratosphere and extends to 85 kilometers (53 miles) above the Earth’s surface. The temperature decreases from negative 15 degrees Celsius (5 degrees Fahrenheit) at the stratosphere boundary to negative 120 degrees Celsius (negative 184 degrees Fahrenheit) to the bottom of the thermosphere. Meteors vaporize in the mesosphere, giving it a higher concentration of metallic ions than other atmospheric layers.
The Thinning Thermosphere
From the top of the mesosphere, the thermosphere extends to between 500 to 1,000 kilometers (311 to 621 miles) above the Earth’s surface. Gases are thinner in this layer, absorb ultraviolet and x-ray radiation from the sun and cause temperatures to increase to 2,000 degrees Celsius (3,600 degrees Fahrenheit) near its top. Carbon dioxide gases that contribute to a warming of the troposphere cause a cooling in the thermosphere as they radiate heat back to space. Charged particles from space collide with atoms to create aurora borealis (northern lights) and aurora australis (southern lights).
The Exosphere Layer
The outermost atmospheric layer extends to 10,000 kilometers (6,214 miles) above Earth and is mainly hydrogen and helium. Satellites and spacecraft orbit Earth in this layer. The exosphere temperature increases from 2,000 degrees Celsius (3,600 degrees Fahrenheit) at the bottom of the exosphere, but the very thin air transmits little heat.
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