Earth's atmosphere has a series of layers, each with its own specific traits. Earth's atmosphere can be divided (called "atmospheric stratification") into five main layers, which are the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

The troposphere is the lowest layer of our atmosphere. Starting at ground level, it extends upward to about 10 km (6.2 miles) above sea level. Humans live in the troposphere, and nearly all weather occurs in this lowest layer. Most clouds appear here, mainly because 99% of the water vapor in the atmosphere is found in the troposphere. Air pressure drops, and temperatures get colder, as you climb higher in the troposphere.

More Info: en.wikipedia.org