The Earth's atmosphere is composed of several layers of gases that reach altitudes up to 6,200 miles above sea level. The lowest layer of the atmosphere is known as the troposphere, which reaches altitudes up to 11 miles.
The atmosphere provides oxygen and serves as a barrier to protect the Earth from external radiation and foreign particles from space. The troposphere accounts for the majority of the Earth's air supply and weather functions. As altitude increases, air pressure decreases and temperatures lower due to the lessened density of air molecules until the outer layer of the atmosphere known as the exosphere merges with space.