Rocks at asteroid impact site record fist day of Dinosaur extinction

Figure: an artist’s interpretation of the asteroid impact. The asteroid in the artwork appears much larger that the six-mile rock that scientists have hypothesize actually struck the Earth 66 million years ago. Nevertheless, the image nicely illuminates the great generated as the asteroid rapidly compresses upon impact and the vacuum in its wake. ©NASA/DonDavis

An international scientific team led by The University of Texas and the participation of Centro de Astrobiología (CAB, CSIC-INTA) has analyzed rocks from the central area of Chicxulub crater in the Gulf of Mexico. The analyses have allowed scientists to rebuild the first 24 hours after the impact of the asteroid that ended the age of Dinosaurs.

There are today about 200 known impact craters on Earth. The most important of the all is the Chicxulub impact crater, located at the Yucatán peninsula in Mexico. However, despite its tremendous size (200km) it offers no spectacular views for a visitor. The crater is buried bellow hundreds of meters of sediments that have accumulated through the millions of years that have passed since it was formed. Chicxulub is the only impact event so far known to have caused one of the five big mass-extinctions of life. When the asteroid slammed into the planet, the impact set wildfires, triggered tsunamis and blasted so much sulphur into the atmosphere that it blocked the Sun, which caused the global cooling that ultimately doomed the dinosaurs.

A new study led by researches at the University of Texas Institute of Geophysics (UTIG) and with the participation of the Centro de Astrobiología has confirmed the scenario that scientists have hypothesized. Rock samples extracted from the central area of the crater have been analysed and hard evidence has been found in the tens of meters of rocks that filled the impact crater in the first 24 hours within impact.

The research has been published in the Proceedings of the National Academy of Sciences (PNAS) and builds on earlier work that described how the crater formed and how life quickly recovered at the impact site.

Most of the material that filled the crater within hours of impact was produced at the impact site or was swept in by seawater pouring back into the crater from the surrounding Gulf of Mexico. Just one day deposited about 130 meters of material. This breakneck rate of accumulation means that the rocks record what was happening in the environment within and around the crater in the minutes and hours after impact and give clues about the longer-lasting effects of the impact that wiped out 75% of life on the planet.

As an expert on impact-related sedimentation in craters formed in marine environments, Jens Ormö, researcher at Centro de Astrobiología and co-author of the study, analysed the samples looking at relative variations in factor like type of rock and size or roundness of the fragment, in order to know the way the material has been transported and deposited, and sometimes also from where in the target it came from.

“All that can be read from the sediments laid down during those first moments lets us know how it was on the first day of Cenozoic, the first day of a new age dominated by mammals and eventually by our own species. A species that now by, among other things, massive pollution of oceans and atmosphere has initiated the sixth and latest of the mass-extinctions. Maybe there is still time to learn something from the previous event”, concludes Ormö.


Fuente: UCC-CAB


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