Late eocene impact events and stepwise mass extinctions

Late Eocene extinctions are neither catastrophic nor mass extinctions, but occur stepwise in a sequence of four steps over a period of 3.4 million years. Closely associated with two of the stepwise extinction events are three microtektite horizons; one in the upper part of Globigerapsis semiinvoluta Zone at 38.2 Ma, and two closely spaced layers in the lower part of Globorotalia cerroazulensis Zone at 37.3 and 37.2 Ma. Species extinctions and relative species abundance declines are closely associated with microtektite layers and suggest, but do not prove, a cause-effect relationship between impact events and some of the stepwise mass extinctions.