Troposphere

Lowest layer of Earth's atmosphere

The troposphere is the lowest layer of the atmosphere of Earth. Pronounced , the name comes from Ancient Greek τρόπος (trópos) 'turning, change' and -sphere. It contains 80% of the total mass of the planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur.

From Wikipedia, under CC BY-SA. More on occurri.