Gas molecules in the atmosphere are pulled toward Earth by gravity.

Here's why:

* Gravity is a force of attraction between objects with mass. The Earth has a large mass, and so it exerts a gravitational pull on all objects near it, including gas molecules in the atmosphere.

* The atmosphere is held to Earth by gravity. Without gravity, the gas molecules would simply escape into space.

* Air pressure is a direct result of gravity. The weight of the air above us creates atmospheric pressure, which is another way of understanding how gravity holds the atmosphere in place.

Let me know if you have any more questions!