The lowest layer of the Earth's atmosphere is called the troposphere. This layer extends from the Earth's surface up to about 8 to 15 kilometers (5 to 9 miles) in altitude, depending on geographical location and weather conditions. The troposphere is where nearly all weather phenomena occur, including clouds, rain, and storms, as well as where most of the atmosphere's mass is concentrated. It contains the air that we breathe and is characterized by a decrease in temperature with increased altitude. The boundary between the troposphere and the next layer, the stratosphere, is known as the tropopause.