Impact craters: Lessons from and for the Earth

Abstract

Impact cratering is a ubiquitous process in the solar system. The known population of terrestrial impact craters, however, is relatively small, ∼ 140, and contains a number of biases. The small number and the biases are a result of the highly active geologic environment of the Earth, which serves to quickly modify and destroy surface features, such as impact craters. Nevertheless, the basic crater forms of simple and complex structures can be recognized and the ground truth data, particularly on the third dimension, available from terrestrial craters have been of critical importance in constraining various aspects of cratering processes. Some of these constraints, e.g., the concept of the transient cavity, the occurrence and interpretation of shock metamorphic effects, including impact melting, are discussed. Although generally considered an important process with respect to planetary evolution, impact is being increasingly recognized as a process affecting Earth evolution. Impact may have played a role in the origin of the Earth's moon and the evolution of the early crust, atmosphere and biosphere. In more recent geologic time, there is compelling evidence of the involvement of impact in, at least, the Cretaceous-Tertiary mass extinction event. On million year time-scales, impacts on Earth are unlikely to affect the global biosphere but could result in serious damage or even the destruction of human civilization.