 Earth 's atmosphere has no definite boundary , slowly becoming thinner and fading into outer space . Three @-@ quarters of the atmosphere 's mass is contained within the first 11 km of the surface . This lowest layer is called the troposphere . Energy from the Sun heats this layer , and the surface below , causing expansion of the air . This lower @-@ density air then rises , and is replaced by cooler , higher @-@ density air . The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy . 
