| 1 | How old is the Earth? |
| 2 | How were the oceans created? |
| 3 | Originally the atmosphere had none of this gas? |
| 4 | How was the oxygen produced? |
| 5 | How was the nitrogen produced? |
| 6 | As more oxygen was produced, what was formed? |
| 7 | How many oxygen atoms does ozone contain? |
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