Earth's Atmosphere

Due to the increase in the different gasses in our atmosphere, the atmosphere is becoming more and more thinner and slowly merging with space at about 100 km. This boundary is known as the Stratosphere (Karman line). The atmosphere protects the earth from energetic X-rays as well as keeps the temperature at an average of 15 degrees. This is done by reflecting excess sunlight away from the earth.

BBC Bitesize

 

In basic terms the Earth's atmosphere protects the Earth from heating up and absorbing large amounts of different radiation such as x-rays, gamma rays etc. It also protects us from meteorites to an extent as when the meteorite enters the Earth's atmosphere most of the mass is burned reducing the size of the impact.
 

Gas:	Percentage in atmosphere:
Nitrogen	78%
Oxygen	21%
Argon	1%
Carbon dioxide (at present)	0.04%
Water vapour	1%