Who is Geologists from The Origin of Species and what is their importance?

Geologists are scientists who study the earth and its history, particularly its non-living aspects. Darwin relies heavily on geological evidence. It is used, for one, to prove that the earth has existed for a sufficiently long time for natural selection to produce the variety of species that exist today. Geology provides evidence of this by measuring the amount of erosion found on certain rock formations. Since the rate of erosion can be measured, the age of the cliffs can likewise be determined. In many cases, the erosion of cliffs suggests that the earth is millions of years old, at the youngest. Geology also provides for explanations of the migration of animals by showing evidence of islands breaking off from continents and the occurrence of an ice age in recent history.