When Earth got pummeled

Abstract

The frequency of impacts on Earth s surface increased about 290 million years ago Collisions and impact processes have been important throughout the history of the solar system, including that of Earth. Small bodies in the early solar system, the planetesimals, grew through collisions, ultimately forming the planets. Recognizing the remnants of impact events on Earth is difficult because terrestrial processes either cover or erase the surface expression of impact structures in geologically short timespans. Because Earth and the Moon are subjected to the same flux of impactors, the latter s crater record serves as a proxy for that of Earth. On page 253 of this issue, Mazrouei et al. (1) report that infrared images of the Moon taken by the Lunar Reconnaissance Orbiter Diviner instrument can be used to estimate the ages of young lunar craters. They find the impact rate increased within the last ∼500 million years.