The Earth's Atmosphere

The atmosphere surrounds Earth and protects us by blocking out dangerous rays from the sun. The atmosphere is a mixture of gases that becomes thinner until it gradually reaches space. It is composed of Nitrogen (78%), Oxygen (21%), and other gases (1%).
Oxygen is essential to life because it allows us to breathe. Some of the oxygen has changed over time to ozone. The the ozone layer filters out the sun's harmful rays. Recently, there have been many studies on how humans have caused a hole in the ozone layer.
Humans are also affecting Earth's atmosphere through the greenhouse effect. Due to increases in gases, like carbon dioxide, that trap heat being radiated from the Earth, scientists believe that the atmosphere is having trouble staying in balance creating the greenhouse effect.
The atmosphere is divided into five layers depending on how temperature changes with height. Most of the weather occurs in the first layer.

The website:http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/overview.html