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5,000 mya to today

Our place in nature - timeline 1

1. It is now thought that the first living cells came into existence over 4000 million years ago. They acquired energy from energy-containing chemical compounds formed through the action of UV radiation and electrical discharges in storms 2. The first organisms capable of capturing the energy from sunlight for building complex organic molecules were cyanobacteria ('blue-green algae'). They were in existence by 2500 million years ago - possibly 1000 million years before this. Their presence resulted in the release of oxygen into the atmosphere 3. Jawless cartilaginous fishes were in existence 510 million years ago (perhaps by 600 million years ago). The first modern, bony, fishes appeared about 395 million years ago 4. About 400 million years ago some plants, insects and other invertebrates, and eventually vertebrates, invaded the land. This was made possible by the diminishing intensity of UV radiation from the sun due to the development of the ozone layer in the stratosphere. 5. 300 million years ago was the heyday of amphibians 6. A mass extinction occurred 250 million years ago. 90% of all marine species and 70% of land vertebrates were wiped out 7. Early reptiles with scales appeared around 240 million years ago. 8. By 200 million years ago early mammals were in existence. They probably laid eggs and were descended from mammal-like reptiles. Early dinosaurs also appeared at about this time 9. Around 160 million years ago the first flowering plants appeared, a great diversification was taking place among the dinosaurs 10. A mass extinction occurred 65 million years ago. All species of dinosaurs disappeared as well as many other animal species. Among the survivors were some small shrew-like, tree dwelling primates which included ancestors of humankind.

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