The history of life involves enormous change. Major life forms have appeared, flourished, and died out. Reptiles ruled the earth for nearly 200 million years. At some points in earth history many species went extinct in a short time. These are called mass extinctions , a topic we will revisit shortly.
Extinction is commonplace.
The vast majority of taxa have gone extinct. The Earth's geological and biological histories are intertwined. Volcanism and meteorite impacts apparently contributed to mass extinctions. Climate change has been a constant of earth history, and also is a causal factor in both speciation and extinction. A mass extinction is defined as a relatively brief period in which more species become extinct than at other times.