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| c. 4 billion years ago |
| | | The earth's surface settles into a heaving turmoil of rock and water | |
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| c. 3.5 billion years ago |
| | | Fossilized bacteria have been found in rock 3.5 billion years old in Africa | |
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| c. 3 billion years ago |
| | | Single-celled water creatures, such as algae, begin the 2-billion-year process of evolving into slightly more complex forms of life | |
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| c. 1 billion years ago |
| | | Sponges and jellyfish drift in the sea, to be joined later by more purposeful shrimps and lobsters | |
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| c. 500 million years ago |
| | | The earliest known creature with a skeleton evolves as a form of fish | |
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| c. 400 million years ago |
| | | Plants, previously living only in the seas and rivers, begin to establish themselves on land | |
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| c. 350 million years ago |
| | | Insects become the first creatures capable of living their full life span out of the water - and the first to master flight | |
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| c. 340 million years ago |
| | | Amphibians develop lungs, enabling them to live on land as well as in the water | |
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| c. 300 million years ago |
| | | Reptiles develop evolutionary advantages for adaptation to a wide range of environments | |
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| c. 250 million years ago |
| | | The entire land surface of the earth merges into a single continent, known as Pangaea, which after about 50 million years splits in two | |
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