Earth's atmosphere 2
Storyboard Szöveg
- 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.
- As the temperature cooled, 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.
- Around 3.5 billion years ago, life appeared. The first living things were simple bacteria. Around 2.7 billion years ago, the first algae appeared and photosynthesis began. It converted the carbon dioxide into oxygen. Over the next billion years plants and eventually animals evolved.
- 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 etc.) and thus reduced the carbon dioxide in the atmosphere.
- For the last 200 million years the earths atmosphere has stayed much the same. About 80% nitrogen, 20% oxygen, and small proportions of carbon dioxide, water vapour and noble gases.
- Human activities are increasing the amount of greenhouse gases in the atmosphere. Burning fossil fuels and deforestation are increasing carbon dioxide. Cattle and rice farming are increasing methane. This is causing the temperature to increase, resulting in global climate change.
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