Hello!
Because as you get closer to the surface of the earth, the more air that is on top of you. At the top of the atmosphere, there is less air, and everything is a vacuum, where you have no weight. When you get close to the earth, the weight of the air builds until it when you're at the very lowest point of the earths surface, all the air in the atmosphere above you is pressing down.
Thank You!
They lack a cell nucleus.
30mi/6hrs is a speed of 5 mph, which converts to a pace of 12 min/mi.
Please find attached photograph for your answer. Hope it helps. Please do comment