Hi Keaton,

That's a great question. Our Sun is constantly emitting energy into space in the form of electromagnetic radiation. Visible light, ultraviolet light, x-rays, radio waves, and infrared radiation (or "heat" radiation) are all part of the electromagnetic spectrum. All of these different types of electromagnetic radiation travel through space as electromagnetic waves, or photons, until they reach the Earth. Our atmosphere can block or absorb some parts of the electromagnetic spectrum, like x-rays, while other parts of the electromagnetic spectrum pass through, like visible light and infrared radiation.

Interestingly enough, the infrared radiation from the Sun does not directly heat the lowest layer of the Earth's atmosphere, called the troposphere. We live in the troposphere. The infrared radiation from the Sun passes through the atmosphere, where it is absorbed by the ground. The heat energy that is re-radiated by the ground actually warms the lower part of the atmosphere. This indirect heating mechanism is the main reason why we have weather here on Earth. You may have heard that warm air rises, while cooler air sinks. Warm air close to the Earth's surface will rise, while cooler air at higher altitudes will sink, resulting in huge convection currents in the atmosphere. These convection currents, coupled with the Earth's rotation produce our weather.

The temperature of the Earth's atmosphere varies in a very unusual way with altitude because the different layers are heated by different processes. As we leave the surface of the Earth and go up in altitude through the troposphere, the temperature begins to decrease with increasing altitude, because this layer is heated from the ground upwards. However, when we reach the next atmospheric layer, the stratosphere, the temperature actually increases with altitude because it is heated by a different process.

You can learn more about the atmosphere and how temperature varies with altitude here:

http://www.windows.ucar.e...mosphere/layers.html

Kris