Why Does Air Get Thinner the Higher You Go?

Have you noticed that when you go to higher altitude places that it is harder to breathe? That is caused by something called Air Pressure.

Air pressure is the is the thing that happens when gravity in the earth pulls the air particles down, we can’t feel this pressure because our bodies push an equal amount of pressure outwards. 

The higher you go there is less air because gravity is pushing all the air particles to the ground so there is less air particles in the sky.