The Earth's atmosphere protects us from significant exposure to cosmic rays. Without the atmosphere, the Earth's surface would be a deadly environment. Even if we could survive without air, cosmic rays would quickly damage the DNA which makes up our living cells. As a cosmic ray enters the upper atmosphere, it collides with a particle, usually a nitrogen or oxygen molecule, producing a shower of lower energy particles. Many of these lower energy particles are absorbed by the Earth's atmosphere as they travel down to the surface.