QUIZ 19a. More on earth's atmosphere formation

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(a) For 200 million years the proportions of different gases in the atmosphere have been much the same as they are today, that is about (%) nitrogen; about (%) oxygen and small amounts of various other gases, including carbon dioxide (%), vapour (variable with humidity) and gases.

(b) During the first billion years of the Earth's existence there was intense . This activity released the gases which then formed the early atmosphere and water vapour which to form the oceans.

(c) During this period the Earth's atmosphere was probably mainly and there would have been little or no oxygen gas (like the atmospheres of Mars and Venus today). There would also have been water vapour, and small proportions of (CH4and (NH3).

(d) When evolved and successfully colonised most of the Earth's surface (land and sea), the atmosphere gradually became more and more '' with oxygen from the process of . This meant that, gradually, there were fewer habitats suitable for microorganisms which could not oxygen

(e) Most of the carbon from the carbon dioxide in the air gradually became locked up in as carbonates and fuels as well as being removed by in photosynthesis. The methane in the atmosphere reacted with the to form carbon dioxide and water and the ammonia reacted with oxygen to form .

(f) The atmospheres of other may contain gases such as methane, ammonia, carbon dioxide and oxides of sulfur BUT not gas.