AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The Earth's early atmosphere: When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere. No knowledge of other theories is required.
As the early Earth cooled, water vapour in the atmosphere condensed to form liquid oceans.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
As the early Earth cooled, water vapour in the atmosphere condensed to form liquid oceans. Carbon dioxide from the atmosphere then dissolved in this water. Some dissolved carbon dioxide reacted to form insoluble carbonate compounds, which precipitated out of solution and settled as sediments on the ocean floor. This process removed carbon dioxide from the atmosphere, so its concentration fell. For example, carbon dioxide dissolving in water can form carbonate ions, which combine with calcium ions to produce calcium carbonate, CaCO₃, a major component of sedimentary rock such as limestone. The overall effect was a decrease in atmospheric carbon dioxide, helping to shape the atmosphere we have today.
What earns the marks
- Water vapour condensed as the Earth cooled, forming the first oceans.
- Carbon dioxide from the atmosphere dissolved in the ocean water.
- Dissolved carbon dioxide was converted into carbonate compounds.
- Carbonates precipitated out of solution, forming sediments on the sea bed.
- The removal of carbon dioxide from the atmosphere reduced its atmospheric concentration.
Common mistakes and how to put them right
Thinking the oceans formed before the atmosphere cooled.
Put it right by stating that cooling caused water vapour to condense into liquid water, forming oceans.
Confusing dissolving with precipitation.
Put it right: Dissolving is carbon dioxide entering the water, while precipitation is solid carbonate forming and settling out.
Believing carbon dioxide was destroyed completely.
Put it right by explaining it was removed from the atmosphere and stored in oceans and sediments as carbonates.
Exam tips
- Link the sequence clearly: cooling → oceans → dissolving → carbonate precipitation → sediments → less atmospheric carbon dioxide.
- Use the term precipitate correctly, meaning a solid formed from solution, and name an example such as calcium carbonate.
- When asked to explain a decrease, refer to removal from the atmosphere rather than destruction of carbon dioxide.
Try the lesson
The start of the The Earth's early atmosphere: When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere. No knowledge of other theories is required. lesson, made from checked teaching notes for this specification point.
Have a go first
When the oceans first formed on the early Earth, which gas from the atmosphere dissolved in the water?
Listen
As the early Earth cooled, water vapour in the atmosphere condensed to form liquid oceans. Carbon dioxide from the atmosphere then dissolved in this water. Some dissolved carbon dioxide reacted to form insoluble carbonate compounds, which precipitated out of solution and settled as sediments on the ocean floor. This process removed carbon dioxide from the atmosphere, so its concentration fell. For example, carbon dioxide dissolving in water can form carbonate ions, which combine with calcium ions to produce calcium carbonate, CaCO₃, a major component of sedimentary rock such as limestone. The overall effect was a decrease in atmospheric carbon dioxide, helping to shape the atmosphere we have today. A strong answer earns marks for these points. Water vapour condensed as the Earth cooled, forming the first oceans. Carbon dioxide from the atmosphere dissolved in the ocean water. Dissolved carbon dioxide was converted into carbonate compounds. Carbonates precipitated out of solution, forming sediments on the sea bed. A common slip: Thinking the oceans formed before the atmosphere cooled. Instead, stating that cooling caused water vapour to condense into liquid water, forming oceans. Exam tip: Link the sequence clearly: cooling → oceans → dissolving → carbonate precipitation → sediments → less atmospheric carbon dioxide.
Key words
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Formation of the oceans by condensation
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Solubility of carbon dioxide in water
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Precipitation of carbonates and sediment formation
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Reduction of atmospheric carbon dioxide over time
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See every definition
- Formation of the oceans by condensation
- As the early Earth cooled, water vapour in the atmosphere condensed to form liquid oceans.
- Solubility of carbon dioxide in water
- Carbon dioxide from the atmosphere dissolved in the ocean water.
- Precipitation of carbonates and sediment formation
- Carbonates precipitated out of solution, forming sediments on the sea bed.
- Reduction of atmospheric carbon dioxide over time
- The removal of carbon dioxide from the atmosphere reduced its atmospheric concentration.
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