Air

The Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity.

Constituents

It contains roughly (by molar content/volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor.

This mixture of gases is commonly known as air.

Protection offered

The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

Space-atmospheric

There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space.

Three quarters of the atmosphere's mass is within 11 km of the planetary surface.