Troposphere is the layer that is closest to the Earth. It is a small layer. It is about 10 miles thick. Troposphere is made up of oxygen and nitrogen. Oxygen and nitrogen are gases that are important for living being. In troposphere these two gases are mixed so that we can breathe and live.
Troposphere is warm near the Earth, but gets colder in higher places. That is why tops of the mountains are usually colder than places that are lower. Most of our weather takes place in the troposphere.