the vast majority of human activity takes place in just one atmospheric layer. which one
Troposphere
Troposphere
 troposphere 
wiki:11623510
Troposphere [SEP] Introduction
The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place. It contains 75% of the atmosphere's mass and 99% of the total mass of water vapour and aerosols. The average height of the troposphere is in the tropics, in the middle latitudes, and in the polar regions in winter. The total average height of the troposphere is . The lowest part of the troposphere, where friction with the Earth's surface influences airflow, is the planetary boundary layer. This layer is typically a few hundred meters to deep depending on the landform and time of day.