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Theory of Evolution

Evolution has taken place over millions of years and is responsible for all the living things on Earth today. There are different views and theories about the origin of life and the evolutionary process.

How did life start?

planet earth, as seen from space


It is not possible to be certain how life on Earth began. We do know that:

  • the Earth is about 4,500 million years old
  • there is evidence that living things existed on Earth at least 3,500 million years ago
  • no one was there to record how life began
  • early Earth was hotter and the atmosphere consisted mostly of carbon dioxide (with other gases such as ammonia and methane)

Scientific theories

Through the study of simple organisms and the chemistry of living things, we can develop scientific theories about how life on Earth began. The main theory is that living things developed from molecules that could replicate, or copy, themselves, rather like DNA [DNA: The material inside the nucleus of cells, carrying genetic information. DNA stands for Deoxyribonucleic Acid. ] does.

There are two possible origins for these replicating molecules:

  • they were produced by the conditions on Earth at the time
  • they came from somewhere else, such as another planet in our Solar System, or further out in space

Over many millions of years these molecules joined with other molecules, becoming gradually more complex and dependent on each other. The process of evolution by natural selection eventually led to all of the different living things that we see on Earth today.

Back to Life on Earth index

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