Life on Earth
- Scientists do not know how life started, but there are many theories
- Experiments by Miller and Urey showed how amino acids, molecules that are essential for life, could have been formed
- They fired an electric spark, representing lightening, in a mixture of the gases methane, ammonia and hydrogen plus water
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- A mixture of chemicals formed, including amino acids
- This is sometimes called a primordial soup meaning a rich mixture of chemicals essential for life
- However, these experiments do not show how life itself could have started because there is no explanation of how biological matter was formed from non-biological matter
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Evolving of Air
- There are several theories about the early atmosphere and the changes since the earth formed about 4.5 billion years ago
- Some scientists think that the gases that formed the early atmosphere came form inside the earth, from volcanic activity
- Another theory is that the gases came from comets colliding with the earth
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- At first there is no oxygen, little nitrogen and lots of carbon dioxide
- Slowly the carbon dioxide decreases and the nitrogen levels increase
- Oxygen only appears when carbon dioxide has decreased and then the oxygen levels increase when life appears
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- Carbon dioxide reacted with rocks and much became trapped in them.
- The evolution of algae some 3000 million years ago, and subsequently plants which successfully colonised the Earth’s surface, led us towards the present atmosphere.
- Their photosynthesis replaced carbon dioxide with oxygen.
- Over a period of time billions of tonnes of carbon dioxide became locked up in fossil fuels.
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