Earth is surrounded by a blanket of air, composed mainly of nitrogen and oxygen. This is the atmosphere, which extends hundreds of kilometers above Earth's surface and protects our planet from harmful radiation from the sun. The atmosphere also plays a major role in water and energy transport. The temperature and pressure varies with altitude throughout Earth's atmospheric layers. Gases are compressible (squeezable), so Earth's gravity causes atmospheric pressure to increase with decreasing elevation. This means that atmospheric pressures are highest in the troposphere, near Earth's surface.

The temperature profile of the atmosphere is not quite as simple. Temperatures vary in Earth's atmosphere as a result of the chemical and physical properties of each layer, as well as the amount of solar radiation that each layer receives.

The thermosphere receives a great deal of solar radiation and is therefore strongly affected by solar energy. UV radiation is absorbed in this layer and causes temperatures to raise. In the mesosphere, the layer beneath the thermosphere, atmospheric pressure is so low that there are not enough air molecules to absorb much solar radiation. Therefore, temperatures drop in this layer. The stratosphere and troposphere contain 99% of the atmosphere's mass. As the Earth's surface absorbs solar radiation, it warms the lower parts of the troposphere. This warm air rises up through the troposphere through the process of convection (similar to what you learned about in the unit on plate tectonics). Because temperature and pressure drop with increasing altitude in the troposphere, convection causes a lot of turbulence in this layer. In contrast, the stratosphere is relatively stable because the temperature increases with altitude in this layer, which prevents convection from taking place. Temperatures increase with altitude because of the ozone layer, which you'll learn more about in a few pages.

In the interactive lesson on the next page, explore how Earth's atmospheric temperature, pressure, and composition are related to altitude.

Source: Oklahoma Climatological Survey