The Earth's atmosphere is unique among planets in the solar system, primarily consisting of nitrogen, oxygen, argon and carbon dioxide. If you look at a cross-section of the atmosphere, you'll see stratified layers starting at ground level and ending at the edge of space. Each layer has a distinct role in maintaining the planet's life-affirming properties.

The troposphere extends to 20 kilometers (12 miles) above the Earth's surface. The vast majority of the Earth's weather occurs in this layer, which contains 75 percent to 80 percent of the atmosphere's mass. The warm ground heats the troposphere, whose temperatures decrease with altitude. At the top of the troposphere the temperature is a chilly negative 55 degrees Celsius (negative 64 degrees Fahrenheit). The atmospheric pressure also decreases with altitude, and the thinner air requires mountain climbers to use portable oxygen tanks to breath.

The stratosphere can be found at altitudes between 20 and 50 kilometers (12 and 31 miles). Temperatures rise as altitude increases in the stratosphere, and this leads to little mixing of air. Commercial airliners, which reach cruising altitude within the stratosphere, take advantage of this stability. The stratosphere is also home to the ozone layer, which protects the biological organisms from harmful ultraviolet radiation.

The mesosphere extends between altitudes of 50 and 85 kilometers (31 to 53 miles). Very little is known about the mesosphere, since methods to deploy scientific instruments to this altitude are difficult. Planes do not fly high enough to reach the mesosphere, and satellites orbit at the higher altitudes. Observational data, however, indicates that the majority of the meteors which impact Earth burn up in the mesosphere.

The thermosphere extends between the altitudes of 85 and 1,000 kilometers (53 and 621 miles). Although the thermosphere is considered a part of the Earth's atmosphere, the most generally accepted definition states that space starts at about 100 kilometers (62 miles). This boundary is known as the Karman line, and it is the official boundary recognized by the International Aeronautic Federation. Indeed, satellites and the International Space Station orbit the Earth within the thermosphere. Adding to the complexity of the atmosphere, another layer of gas, which mainly consists of hydrogen, helium and carbon dioxide, is found above the thermosphere. Named the exosphere, it is officially part of the Earth's atmosphere. The air density is so low, however, that it is considered to be interplanetary space.