Why was gravity necessary for stability of Earth's atmosphere?

Correct answer: It keeps gases near Earth

The direct answer is A: gravity keeps gases near Earth. An atmosphere is a layer of gases surrounding a planet. Gas particles move in many directions, and without sufficient gravitational pull, lighter gases could escape into space. Earth's gravity pulls atmospheric gases toward its surface and helps hold them around the planet. Therefore option A is correct. Option B is wrong because gravity does not remove all oceans; it helps keep ocean water on Earth. Option C is wrong because gravity does not make the crust disappear; the crust is Earth's solid outer layer. Option D is wrong because gravity does not cool the Sun; the Sun's temperature is controlled by its internal nuclear processes. The exact idea is: Earth's mass creates gravity, gravity attracts gases, and this helps maintain a stable atmosphere. Memory cue: gravity means “hold close,” so it holds air close to Earth.