As the earth cooled down, water vapour in the air condensed to form the oceans. Carbon Dioxide in the atmosphere then dissolved into the oceans. Scientists believe half of the world's carbon dioxide was lost through this way
Some marine organisms use dissolved carbon dioxide to make shells of calcium carbonate and as the creatures die their shells fall and become sediment. Over millions of years the layers of sediment compact to form sedimentary rock.
Limestone is mostly calcium carbonate.
Scientists believe life started 4 billion years ago. About 1 billion years ago, some organisms developed the ability to photosynthesise.
Photosynthesis is taking in carbon dioxide, releasing oxygen.
Over time, more photosynthesising organisms evolved. Increasing levels of photosynthesis sped up the rate at which Carbon Dioxide was removed from the atmosphere and the rate oxygen was added to th atmosphere.
Key Words:
Sedimentary Rock
Limestone
Photosynthesise
Questions:
1. What is the main substance in limestone?
2. What are two ways carbon dioxide was removed from the early atmosphere?
3. Explain how the amount of oxygen in the atmosphere gradually increased?
What you should know:
- 1.5 Be able to describe how the amount of carbon dioxide in the atmosphere was reduced by:
- a) the dissolution (dissolving) of carbon dioxide into the oceans
- b) the later incorporation of this dissolved carbon dioxide into marine organisms which eventually formed carbonate rocks
- 1.6 Be able to explain how the growth of primitive plants used carbon dioxide and released oxygen by photosynthesis and consequently the amount of oxygen in the atmosphere gradually increased
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