Eli5: how does the earths atmosphere work? E. G how does the oxygen not fade away into the cosmos

Question

I’ve had a conversation with a guy that claimed “it’s a myth”. An obvious face-palm, I know, but I realized I’d like to know.

In: 71

Answer 1

If a gas is heavy enough, gravity will keep it within roughly 100 km of the Earth’s surface. This includes oxygen (O2), nitrogen (N2), Carbon Dioxide (CO2), etc. Lighter molecules like hydrogen (H2) or helium (He2) can get enough energy from the sun to reach escape velocity (the speed needed to escape the Earth’s gravitational well) and slowly bleeds off into space. That’s why helium is a limited resource on Earth.