![]() Iridium levels in this layer were as much as 160 times above the background level. The Alvarezes and colleagues reported that it contained an abnormally high concentration of iridium, a chemical element rare on Earth but common in asteroids. The main evidence of such an impact was contained in a thin layer of clay present in the Cretaceous–Paleogene boundary (K–Pg boundary) in Gubbio, Italy. In the late 1970s, geologist Walter Alvarez and his father, Nobel Prize–winning scientist Luis Walter Alvarez, put forth their theory that the Cretaceous–Paleogene extinction was caused by an impact event. The date of the impact coincides with the Cretaceous–Paleogene boundary (commonly known as the K–Pg or K–T boundary) and it is now widely accepted that the devastation and climate disruption from the impact was the cause of the Cretaceous–Paleogene extinction event, a mass extinction in which 75% of plant and animal species on Earth became extinct, including all non- avian dinosaurs. Evidence for the impact origin of the crater includes shocked quartz, a gravity anomaly, and tektites in surrounding areas. Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. ![]() Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. The crater was discovered by Antonio Camargo and Glen Penfield, geophysicists who had been looking for petroleum in the Yucatán Peninsula during the late 1970s. It is the second largest confirmed impact structure on Earth, and the only one whose peak ring is intact and directly accessible for scientific research. The crater is estimated to be 180 kilometers (110 miles) in diameter and 20 kilometers (12 miles) in depth. It was formed slightly over 66 million years ago when a large asteroid, about 10 kilometers (6.2 miles) in diameter, struck Earth. Its center is offshore near the communities of Chicxulub Puerto and Chicxulub Pueblo, after which the crater is named. The Chicxulub crater ( IPA: ) is an impact crater buried underneath the Yucatán Peninsula in Mexico. Chicxulub crater (Mexico) Show map of Mexico
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