Starter quiz
- Earth's atmosphere comprises approximately 21% of which gas?
- 'oxygen' ✓
- What is the percentage of carbon dioxide in Earth's atmosphere?
- 78%
- 21%
- 1%
- 0.04% ✓
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- How old is Earth thought to be?
- 4 million years
- 4.5 billion years ✓
- 2 million years
- 200 billion years
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- The atmosphere on Earth has been in roughly the same proportions for how many million years?
- '200' ✓
- What name is given to the layer of gas that surrounds a planet?
- 'atmosphere' ✓
- What is the name of this process?
- respiration
- combustion
- photosynthesis ✓
- sedimentation
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