Four layers of the earth's atmosphere containing various gases make up the composition of the sky. The layers of the atmosphere are divided into the troposphere, the stratosphere, the mesosphere and the thermosphere. The atmosphere's divisions occur according to temperature fluctuations.
Nitrogen and oxygen are the two major gases present in the atmosphere. Nitrogen accounts for 7 percent of the earth's atmosphere while oxygen comprises 21 percent. Several other gases are present, but they make up a very small portion of the total gases. One smaller gas group that exists in the atmosphere is the greenhouse gas group. Carbon dioxide is the prominent gas from this group. Greenhouse gases in excess can be detrimental to the earth as they contribute to global warming, but when the gases are in proper proportions they aid in warming the earth for inhabitants to survive comfortably.
The troposphere, the layer of atmosphere closest to the earth, is where weather takes place. The word "troposphere" originates from the word "tropein," which means "to turn or change." The troposphere extends approximately seven miles from the earth's surface and has pressure ranges from 1000-200 millibars (a measure of atmospheric pressure). Temperature decreases with increasing height into the troposphere. Wind increases with height. Moisture concentration decreases with height. Oxygen is not able to survive in any layer higher than the troposphere because it has low density.