The Earth's early atmosphere
The Earth formed about 4.5 billion years ago. Scientists believe that its early The layers of gases that surround the Earth. The important gases in the atmosphere are nitrogen, oxygen and carbon dioxide. was produced by volcanic activity.
Composition
The early atmosphere probably contained:
- little or no oxygen
- a large amount of carbon dioxide
- water vapour
- small amounts of other gases, such as ammonia and methane
Scientists cannot be sure about the early atmosphere, since it formed so long ago. They can only analyse evidence from other sources.
Oxygen
Some ancient rocks contain iron A substance formed by the chemical union of two or more elements. that break down in the presence of oxygen. They could only have formed if there was little or no oxygen at the time.
Carbon dioxide and water vapour
A A landform created by an area in the Earth's crust through which lava, steam and ash may erupt. releases large volumes of carbon dioxide and water vapour. Since the early atmosphere was produced by volcanic activity, it was likely to have contained a large amount of carbon dioxide and water vapour.