What causes air pressure on earth?
All of the air is pulled toward the center of the Earth by gravity. If you dive deep into water, you will feel the water press on you more and more as you go deeper. The same is true with air pressure. We live at the bottom of a great ocean of air. If you travel up, for instance by climbing up a mountain, you will have less air above you to press down on you. By checking a barometer you can tell just how much less pressure. The air, being a gas, doesn’t end and have a “surface” like the ocean does. As you go up, it just gets thinner and thinner until it finally has the same density as interstellar space. The air pressure can change from moment to moment also. When the sun comes up in the morning it starts to heat the air a little bit as it travels through it. But the main heating of the air comes as the sun heats the ground (or water) and the air picks up this heat and expands during the day. This expanded air has a slightly higher pressure than cooler air and it starts to rise and pus
