Why Does the Earth's Atmosphere Stay on the Earth?

The earth's atmosphere is kept close to the earth by gravity. Just as the earth's gravity keeps you firmly on the ground, it also acts on the gases of the earth's atmosphere, holding it in place and allowing us to breathe.

Earth's Early Atmosphere

As the earth formed, its gravitational pull attracted elements from nearby space, such as hydrogen and helium. These formed the earth's initial atmosphere.

Volcanic Additions

As the earth's crust cooled, erupting volcanoes spewed nitrogen and other gases into the earth's atmosphere. The earth's gravity prevented the gases from escaping, and they became part of the atmosphere.

The Arrival of Oxygen

Oxygen entered the earth's atmosphere through plant photosynthesis, as well as the breakup of water molecules by ultraviolet light.

Thickest at the Bottom

The earth's gravitational pull grows stronger the closer you get to the earth's surface. Since the gases of the atmosphere can be compressed, the atmosphere is thickest at the bottom. The farther one travels from the earth's surface, the thinner the atmosphere, until it dissolves into the vacuum of space.

The Troposphere

Today, the bottommost layer of the earth's atmosphere, called the troposphere, is made up mostly of nitrogen and oxygen, other trace gases such as carbon dioxide, and water vapor. All of the earth's weather happens in the troposphere.

References

• Amazing Space: A Book of Answers for Kids; Ann-Jeanette Campbell; 1997
• Eastern Illinois University: Origin of the Earth's Atmosphere