In addition to Earth, the terrestrial planets of Mars, Venus and Mercury have oxygen in their atmospheres. The atmospheres of these planets, along with the others in the solar system, contain many different substances. The amount of oxygen in their atmospheres varies; Earth contains the most oxygen while Mars and Venus have smaller amounts and more carbon dioxide.
The atmospheres of all planets, regardless of composition, contain the same basic substances. They form from a mixture of gases and particles, performing tasks like regulating temperatures and supporting or failing to support life. Of all the elements in the atmosphere, oxygen takes the lead as primary supporter of life. It exists in greatest abundance around the Earth, which in turn serves as home to far more living organisms than other planets. Earth, like other terrestrial planets, features air deriving from heavy gases and compounds. Its atmosphere forms from nitrogen too, and to a lesser extent, carbon dioxide, argon, ozone and helium. The Earth's atmosphere contains approximately 22 percent oxygen, which exceeds the oxygen content in other planetary atmospheres. In addition to oxygen, some planets have other properties conducive to life, such as water and predictable temperatures. However, even the planets with atmospheres closest Earth's support much less life.