There is no clearly defined top to our atmosphere. About 90 percent of it lies between the surface and a height of about 10 miles (16 km). Above
Layers of the atmosphere
COMPOSITION OF THE PRESENT ATMOSPHERE
Major constituents nitrogen oxygen argon water vapor
Minor constituents carbon dioxide neon helium methane krypton hydrogen nitrous oxide carbon monoxide xenon ozone
Trace constituents ammonia nitrogen dioxide sulfur dioxide hydrogen sulfide
CO2 Ne He CH4 Kr H2 N2O CO Xe
365 p.p.m.v. 18 p.p.m.v. 5 p.p.m.v. 2 p.p.m.v. 1 p.p.m.v. 0.5 p.p.m.v. 0.3 p.p.m.v. 0.05-0.2 p.p.m.v. 0.08 p.p.m.v. variable
(p.p.m.v. means parts per million by volume; 1 p.p.m. = 0.0001 percent. p.p.b.v. means parts per billion by volume; 1 p.p.b. = 0.0000001 percent.)
this height, the remainder of the atmosphere extends to at least 350 miles (550 km) from the surface. Beyond that it merges imperceptibly with the molecules and atoms of interstellar space and the outer fringes of the solar atmosphere.
The density of the air decreases rapidly with height, so that the molecules in its outermost reaches are so widely scattered that they rarely collide with one another. Air temperature also changes with height. If you climb a mountain you will find the air is colder the higher you go, and even near the equator there are mountains that have snow on their peaks. So we are used to the idea that the higher you climb the colder you will feel. This is true while you remain fairly close to the surface,
Stratosphere and stratopause
but there are other regions of the atmosphere where the temperature increases with height—eventually to about 1,830°F (1,000°C) when you reach an altitude of 310-620 miles (500-1,000 km). As the diagram shows, the atmosphere is arranged in layers, one above another, and the layers are produced by the way temperature changes with height within them.
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