The atmosphere, the “skin” of gas that surrounds Earth, consists of five layers that are differentiated by temperature:

The troposphere is the lowest level; it averages about 7 miles (11 kilometers) in thickness, varying from 5 miles (8 kilometers) at the poles to 10 miles (16 kilometers) at the equator. Most clouds and weather form in this layer. Temperature decreases with altitude in the troposphere.

The stratosphere ranges between 7 and 30 miles (11 to 48 kilometers) above Earth’s surface. The ozone layer, important because it absorbs most of the sun’s harmful ultraviolet radiation, is located in this band. Temperatures rise slightly with altitude to a maximum of about 32°F (0°C).

The mesosphere (above the stratosphere) extends from 30 to 55 miles (48 to 85 kilometers) above Earth. Temperatures decrease with altitude to –130°F (–90°C).

The thermosphere (also known as the heterosphere) is between 55 to 435 miles (85 to 700 kilometers). Temperatures in this layer range to 2,696°F (1,475°C). The exosphere, beyond the thermosphere, applies to anything above 435 miles (700 kilometers). In this layer, temperature no longer has any meaning. The ionosphere is a region of the atmosphere that overlaps the others, reaching from 30 to 250 miles (48 to 402 kilometers). In this region, the air becomes ionized (electrified) from the sun’s ultraviolet rays. This area affects the transmission and reflection of radio waves. It is divided into three regions: the D region (at 35 to 55 miles [56 to 88 kilometers]), the E Region (Heaviside-Kennelly Layer, 55 to 95 miles [88 to 153 kilometers]), and the F Region (Appleton Layer, 95 to 250 miles [153 to 402 kilometers]).