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Q1.
The Earth’s early atmosphere was different to Earth’s atmosphere today.
Scientists think that the Earth’s early atmosphere was like the atmosphere found
on Venus today.
The table below shows the amounts of carbon dioxide and oxygen in the atmospheres of Venus and Earth today.
The percentages of carbon dioxide and oxygen have changed from Earth’s
early atmosphere to Earth’s atmosphere today.
Explain the processes that led to these changes.
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At first, Earth’s atmosphere had a lot of carbon dioxide and very little oxygen. Volcanic eruptions released gases like carbon dioxide and water vapour. As the Earth cooled, the water vapour condensed and formed oceans.
Some of the carbon dioxide dissolved into the oceans. It also reacted to form carbonates, which formed sediments on the sea floor. Later, some of the carbon was locked up in sedimentary rocks and fossil fuels.
Then, algae and plants evolved. They started to absorb carbon dioxide for photosynthesis. This process also released oxygen. Over time, this increased the amount of oxygen in the atmosphere and reduced the amount of carbon dioxide.
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