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Across 3. This was the main gas present in the early atmosphere 4. Part of the earth we live on 6. Sudden movement of the Earth's plates. 8. These currents are responsble for the movement of the Earth's plates 11. The early atmosphere was very much like the atmosphere on this planet today 13. Makes up less thean 1% of the atmosphere and used in light bulbs 15. This is caused by carbon dioxide in the atmosphere 16. A gas found in small quantites in the original atmospahere 18. These release carbon dioxide when burned 19. The source of heat for convection currents 20. A type of rock formed from carbon dioxide trapped in the rock 21. Plants were responsible for producing this gas. 22. the area where 2 plates meet 23. In the first billion years of the Earth's existence this type of activiy was intense

Down 1. Makes up 20% of the atmosphere 2. A noble gas less dense than air and used in balloons 3. The theory used to explain the movement of plates 5. the crust and upper mantle of the Earth are split into these plates. 7. This gas present in the early atmosphere containing nitrogen 9. Part of the Earth made up of molten rock, beneath the crust 10. The centre of the Earth 12. Carbon dioxide in the atmosphere gradually became locked up in these rocks. 14. The water vapour in the early atmosphere condensed to form these 17. Makes up 78% of the atmosphere