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When a gradual change in behavior, morphology, and physiology occurs in organisms that are descendants of pre-existing species, it is called evolution.

Examples of factors causing evolution are random evolution or genetic drift, gene flow, mutation, and natural selection. Evolutionary examples include brightly colored peacocks and Darwin's finches.

The slowly occurring natural events over or under the earth's surface that modifies geological entities are called geologic events.

Examples of geological events include tsunamis, landslides, earthquakes, rockburst, and lava flow (volcanic eruption).

The evolutionary concept through natural selection was introduced by Charles Darwin to determine the inheritance of traits and non-identical species.

Hutton's and Lyell's ideas influenced Darwin's thinking regarding evolution; both scientists (Hutton's and Lyell's) proposed that geologic events in the past occurred by the same process operating today.

This provided an idea to Darwin that the earth's age is more than a thousand years, and one cannot conclude the time taken for the occurrence of evolution.