An atmospheric layer surrounds the earth

We usually don't notice it, but air has weight, and it is held onto the surface by the earth's gravity.

Higher than 400 km above the ground, where the International Space Station (ISS) is flying, there is almost no air. This state where no air exists is called a vacuum. Space is a vacuum.

Generally, altitudes of 100 km or above are considered outer space.

In higher elevations, the amount of air is significantly less. That is why the air becomes thinner as the higher you go up. Running on top of Mt. Fuji would leave you breathless.

Air that is closer to the ground is being squashed since the air supports the weight of the air above it.

In a vacuum, people cannot live without wearing a space suit. But inside the ISS, the air is kept inside, so the astronauts are safe and able to move about without the aid of a space suit.