The Atmosphere The atmosphere of Earth is a layer of gases surrounding the planet and is retained by Earth's gravity. Troposphere The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The bottom of the troposphere begins at the Earths surface, and contains 75% of the entire atmospheres mass. The troposphere is bounded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere. The thickness of the troposphere varies from about 7 to 8 km (5 mi) at the poles to about 16 to 18 km (10 to 11 mi) at the Equator. Stratosphere The second major layer of Earths atmosphere, just above the troposphere, and below the stratopause. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is where weather balloons are launched to investigate the weather beneath. At moderate latitudes the stratosphere is situated between about 1013 km (6.28.1 mi). Mesosphere The mesosphere is directly above the stratopause and below the thermosphere. Temperature decreases with altitude throughout the mesosphere until reaching the mesopause. This is where meteor showers occur. It extends from about 50 to 85 km (31 to 53 miles) above our planet. Thermosphere/Ionosphere The thermosphere is the layer of the Earth's atmosphere directly above the mesopause and directly below the thermopause. Air in the thermosphere is extremely thin, and temperatures increases with altitude. Within this layer, ultraviolet radiation (UV) causes ionization creating northern lights (aurora borealis). It extends from about 90 km (56 miles) to between 500 and 1,000 km (311 to 621 miles) above our planet. Exosphere The exosphere is the uppermost region of Earth's atmosphere as it gradually fades into the vacuum of space. Air in the exosphere is extremely thin - in many ways it is almost the same as the airless void of outer space. Temperatures range from 572F - 30,632F, but youd feel cold because the air is so thin. This is where the International Space Station is orbiting the Earth. This layer extends from ,000 km ( mi) over the Earths surface.