1)by preventing many hazards such as ultraviolet rays and meteors. as meteors fall through the atmosphere, it hits them with small droplets of water, as meteors fly fast, the tiny droplets of water is hitting them so they don't hit earth. the droplets of water are millionths of the size of a rain droplet. even though they are small, they fly fast.
2)keeps the temp at the right level and the right mixes of gases
hope this helps
