Earth's early atmosphere
نص القصة المصورة
- Earth was formed 4.5 billion years ago. At first it was a ball of molten rock and minerals. For the first billion years it was a violent place. The surface was covered in volcanoes which expelled toxic gases into the atmosphere.
- Volcanoes released carbon dioxide, water vapour and nitrogen gas. The water vapour condensed as the Earth cooled, and fell as rain. It fell into the hollows in the crust and formed the first oceans.
- 3.4 billion years ago there were simple organisms who could make their own food. Bacteria then algae evolved. They could use energy from the sun to make their own food. They produced oxygen as a waste product and the oxygen levels rose steadily.
- More and more plants evolved, all photosynthesising, removing carbon dioxide and releasing oxygen. Plants start to colonise the surface of the earth.
- Animals start to evolve. They cannot make their own food and need oxygen to respire.
- Many of the early living organisms could not live with so much oxygen because they had evolved without it. They died out as there were less places for them to live.
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