Earths evolution
نص القصة المصورة
- الانزلاق: 1
- About 4.5 billion years ago, scientists believed that the Earth`s atmosphere contained little or no oxygen; but was mainly carbon dioxide and some nitrogen. Intense volcanic activity produced lots of carbon dioxide, water vapour and nitrogen; along with small amounts of methane and ammonia.
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- As the temperature hit 100°C,water vapour condensed into liquid water and formed the oceans which allowed a lot of the carbon dioxide to dissolve in the water. Carbonates precipitated out and produced sediments (e.g. Limestone), decreasing the amount of CO2 in the atmosphere.
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- Around 3500 billion years ago, life appeared. The first living things were simple bacteria.Around 220 million years ago, the first green plants developed and photosynthesis began. It used up carbon dioxide and produced oxygen.
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- As living things died, some were preserved in rocks as fossils, some became fossil fuels, some shelled creatures became sediments that built up into sedimentary rocks. These events locked up some carbon (in the rocks, soil etc.) and thus reduced the carbon dioxide in the atmosphere.
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- Now, 78% of the Earth`s atmosphere is 80% nitrogen, 20% is oxygen, leaving the rest of the gases as the minority with carbon dioxide, water vapour and noble gases.
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- Human activities are leading to an increasing amount of greenhouse gases in the atmosphere; such as carbon dioxide and methane. One reason why the amount of carbon dioxide is increasing, is that very large quantities of fossil fuels are being burned. Another reason being the increase in deforestation; with trees unable to remove as much carbon dioxide from the air using photosynthesis.
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