Final answer:
The troposphere is the layer of Earth's atmosphere that contains roughly 80% of its mass, where most weather events take place, and extends up to 12 kilometers above sea level.
Step-by-step explanation:
Eighty percent of Earth's atmosphere is compressed within the troposphere. This layer extends from the Earth's surface up to about 12 kilometers above sea level. It is the layer where most weather events originate, and it's characterized by a decrease in air density and temperature as one goes higher. The troposphere is responsible for the conditions that allow life to exist on the planet's surface and is crucial for the Earth's climatic system.