7: Fossils and Evolutionary History of life
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- 7.3: Mass Extinctions
- Extinction (the complete disappearance of a species from Earth) is an important part of the evolution of life on Earth. The current diversity of species is a product of the processes of extinction and speciation throughout the previous 3.8 billion year history of life. There might be 40 million species alive today, but between 5 and 50 billion species have lived at some time during the history of the Earth.