system
Given the following post, respond as if you're commenting on Reddit:
human
Why is hydrogen so prevalent all over the world in oceans and other bodies of water, yet almost completely nonexistent in our atmosphere?

Our atmosphere is almost completely composed of nitrogen, oxygen, and argon. Why not hydrogen?
gpt
Lighter gases move at higher velocity and are thus  more likely to escape Earth's gravitational field and leave the atmosphere. Over the last few billion years, most of the hydrogen has escaped. The same goes for Helium.