In 1980, Luis and Walter Alvarez, Frank Asaro, and Helen Michel proposed that the K-T mass extinction resulted from an asteroid impact. They based their claim on the high levels of the element iridium in the K-T layer. In 1990, Alan Hildebrand and William Boynton discovered, through seismic imaging, a sixty-five million year old impact crater on the northern edge of the Yucatan Peninsula of Mexico.
! To find out more about the Chicxulub Crater, read the articles at the links below.