Earth's atmosphere
Storyboard Text
- 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.
- 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.
- Human activities are increasing the amount of greenhouse gases in the atmosphere. Burning fossil fuels and deforestation is increasing carbon dioxide levels. Farming cattle and rice is increasing methane levels. This is causing the temperature to increase, resulting in global climate change.
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