The diversity of biological species has increased over the past 600 million years of Earth history. After an increase, the diversity reached a constant level for about 200 million years, but then increased steadily. This was due to the changes in species number that reflect the rate of origin of new species with respect to the rate of extinction of existing species. During the increase in species diversity the extinction rate was less than the rate of origin of new species. The rate of speciation has not always been greater than the extinction rate. Sometimes there has been a sharp decrease in the species diversity for very long periods which is termed as mass extinction.

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Chapter 22, Problem 11U

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Introduction:

The diversity of biological species has increased over the past 600 million years of Earth history. After an increase, the diversity reached a constant level for about 200 million years, but then increased steadily. This was due to the changes in species number that reflect the rate of origin of new species with respect to the rate of extinction of existing species. During the increase in species diversity the extinction rate was less than the rate of origin of new species.

The rate of speciation has not always been greater than the extinction rate. Sometimes there has been a sharp decrease in the species diversity for very long periods which is termed as mass extinction.

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