Earth's Atmosphere (1)

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Evidence suggests that the Earth was formed approximately 4.5 years ago. During the first billion years gases were released from volcanoes which covered the surface of Earth. These gases included carbon , water and nitrogen. As the Earth cooled, the water vapour to form the . During the next two billion years conditions existed for and algae to evolve. By the process of , carbon dioxide in the atmosphere was gradually reduced, and greater quantities of were released.

The composition of the atmosphere has remained about the same for the last 200 million years.

atmosphere

The main gas in the atmosphere is , making up 78% of the total amount of gases. is also present which makes up % of the atmosphere. The remaining gases include dioxide, and the noble gases, such as argon and and helium. The noble gases are the least elements.