The Earth's Atmosphere- in 10 steps

The Earth's Atmosphere

1) For 200 milion years, the proportions of different gases in the atmosphere have been much the same as they are today: about four fifths (80%) nitrogen, about one fifth (20%) oxygen, small proportions of various other gases, including carbon dioxide, water vapour and noble gases.

2)During the first billion years of Earth's existence there was intense volcanic activity. This activity released the gases that formed the early atmosphere and water vapour condensed to from oceans.

3) There are several theories about how the atmosphere was fromed. One theory suggests that during this period the Earth's atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like those of Mars and Venus today). There may also have been water vapour and small proportions of methan and ammonia.

4)There…