<P> The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place . It contains approximately 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols . The average depths of the troposphere are 20 km (12 mi) in the tropics, 17 km (11 mi) in the mid latitudes, and 7 km (4.3 mi) in the polar regions in winter . The lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer . This layer is typically a few hundred meters to 2 km (1.2 mi) deep depending on the landform and time of day . Atop the troposphere is the tropopause, which is the border between the troposphere and stratosphere . The tropopause is an inversion layer, where the air temperature ceases to decrease with height and remains constant through its thickness . </P> <P> The word troposphere derives from the Greek: "tropos" for "turn, turn toward, trope" and "- sphere" (as in, the Earth), reflecting the fact that rotational turbulent mixing plays an important role in the troposphere's structure and behaviour . Most of the phenomena associated with day - to - day weather occur in the troposphere . </P>

Since we live at the surface of the earth what layer of the atmosphere would this be