Living on Earth, it is difficult to understand the size of our atmosphere. When we study other planets and Earth from space, we can understand the true thickness of our atmosphere.
Let us try an experiment. If the Earth were a sphere 1 foot in diameter, how thick would our atmosphere be? Start with your hand 2 feet above a table. Lower it slowly until to think you are at the top of the atmosphere … So where did you stop? A foot up? An inch up? The answer is about 1/4 inch.