Most natural extinctions are the result of changes in climate.
Basically, an area's climate is defined by its range in temperature and the amount of moisture it receives. Changes in this climate can be gradual or rapid. Gradual changes that take place over millions of years are generally related to the motion of the earth in its orbit around the sun, or to the motion of the earth's crustal plates. Rapid changes may take place in a matter of years or hundreds of years, and are usually related to dramatic geologic events such as a volcanic eruption or the impact of a meteorite. However rapidly a climate may change, its alteration can change all of the major aspects of an environment, and therefore determine which species can survive and which and cannot.