The layer of Earth's atmosphere that contains the most air is the troposphere. According to NIWA, approximately 75% of all the air in the atmosphere is found in this layer. The troposphere extends from Earth's surface to approximately 5 to 9 miles (8 to 14.5 km) high.
The troposphere is the lowest and densest layer of the atmosphere. It's where most of the weather happens. As you go higher in the troposphere, the air gets thinner and colder.
