Scientists say they have spotted evidence of what it was like on the first day after the dinosaur-killing impact event, thanks to an analysis of rock taken from the famous Chixculub crater.
An asteroid slammed into Earth around 66 million years ago, causing catastrophic events that changed the course of life on this planet. Rock cores recently taken from the resulting crater show evidence of hills, tsunamis, fires, and atmosphere-altering gases, all produced in the first day after the impact.
“It’s so rare in geology that we get to look at the rocks and read a story on the timescale of hours,” Sean Guelick, the study’s first author from the University of Texas at Austin, told Gizmodo.
The impact probably went as follows, based on the rock samples and what we already know about the area surrounding the crater. Initially, the site of the impact was shallow ocean, less than 30 metres deep.
An enormous rock, perhaps a few miles wide, struck and immediately created a large crater. The meteorite would have welled up rock that then collapsed outward, creating a hilly ring. Soon, the ring would have been covered by more than a hundred feet of so-called shocked rock, deformed by the high heat and pressure. The ocean would then have filled the crater, depositing any debris it was carrying.
Finally, the wave that flooded the land would return, depositing soil and other material it picked up from the shore. The process would have taken just hours, according to the paper published in the Proceedings of the National Academy of Sciences.
“You look at a metre of core, and typically you’re looking at millions of years of time. In this case, you instantly made a hole with the impact and buried it with all these dynamic processes,” Guelick said.
A large team of researchers collected the cylindrical rock samples from hundreds of feet below the seafloor and analysed them as part of a mission with the International Ocean Discovery Program, an organisation that funds various seafloor research projects.
Guelick explained that analysis happened onboard the ship, in Houston, Germany, and elsewhere, using medical and chemistry equipment to determine the makeup of the rock. The researchers carefully handled the samples to avoid contaminating them with modern material.
Perhaps most surprising were the soil and charcoal particles they found in the rock, evidence that a tsunami returned to the site of the impact from shore. “It speaks to the energy of the impact,” Katherine Freeman, one of the study’s authors and a professor at Penn State, told Gizmodo. She explained that the patterns in the charcoal were complex, so it’s not as easy as simply saying there were forest fires, but the charcoal was suggestive of high-energy heating that took place hundreds of miles away.
This research doesn’t immediately offer an explanation to how the impact led to a mass extinction. However, the core seemed to be missing sulphur, Guelick said. This could mean that the impact released the sulphur into the atmosphere. A mass extinction would require planetwide catastrophe, and a quick addition of sulphur and other molecules to the atmosphere could have caused global cooling and darkness.
“It’s a really important episode in the evolution of life on the Earth,” H. Jay Melosh, a professor at Purdue University who has collaborated with this team but was not part of this specific paper, told Gizmodo. He said the work was an important documentation of the events that immediately followed the impact. But he pointed out that this is just one paper about one core.
More research into this core and others will help scientists paint a better picture of the event that snuffed out most of life on Earth.