Earth's atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, and thermosphere. Some scientists also count the exosphere, the faint uppermost reaches of the atmosphere that gradually fades into space, as a fifth layer... however, the exosphere is not included in this activity. Click here for additional information on each of these atmospheric layers.
This activity demonstrates the relative thickness of the thin section of the atmosphere that includes the troposphere and stratosphere. These layers are essential to all life on Earth.
Over 99% of the mass of the Earth's atmosphere is contained in the two lowest layers: the troposphere and the stratosphere. Most of the Earth's atmosphere (80 to 90%) is found in the troposphere, the atmospheric layer where we live. This layer, where the Earth's weather occurs, is within about 10 km (6 miles) of the Earth's surface. The stratosphere goes up to about 50 km (31 miles). Gravity is the reason the atmosphere is denser closer to the Earth's surface.
While we think of the atmosphere as a vast ocean of air around us, it is very thin relative to the size of the Earth. The "thickness" of the atmosphere (the distance between the Earth's surface and the "top" of the atmosphere) is not an exact measure. Although air is considered a fluid, it does not have the same well-defined surface as does water. The atmosphere just "fades away" into space with increasing altitude. Compared with the radius of the Earth (6,370 km or 3,949 miles), the depth of the atmosphere is quite shallow.
This activity was developed as part of Project LEARN at UCAR. It includes graphics created by the COMET Program at UCAR.