Across
- 3. Made the Earth richer in oxygen
- 4. Taken in by plants through Photosynthesis
- 7. 78% of Earth's Atmosphere
- 8. The most abundant noble gas found in the air
Down
- 1. A carbon 'sink'
- 2. Turned into rain when the Earth cooled
- 5. 21% of Earth's Atmosphere
- 6. Fossil fuel formed from grazing cattle