It was a normal day in the age of dinosaurs, until it suddenly and vehemently wasn’t. A giant asteroid traveling at about 15 miles per second slammed into Earth, producing an explosion equivalent to more than one billion atom bombs.
Most creatures were doomed even if they survived the initial blast. Clouds blotted out the Sun’s light, eventually killing 75 percent of plant and animal life on the planet. Now, 66 million years after that apocalyptic split-second, scientists have obtained and examined core samples of the debris deposited within the first 24 hours of this major mass extinction.
Led by Sean Gulick, a research professor at the University of Texas Institute for Geophysics, the team used the ancient rocks to reconstruct “the first day of the Cenozoic,” referring to the modern geological period that follows the Mesozoic era of dinosaurs. The team’s study was published on Monday in the Proceedings of the National Academy of Sciences.
This precious record of the fallout is preserved inside the Chicxulub impact crater, a 100-mile-wide hole underneath Mexico’s Yucatán Peninsula. While parts of this formation have been sampled before, Gulick and his colleagues are the first to drill into the “peak ring,” which is an elevated plateau in the middle of the crater.
The team suspected that the peak ring would not have been significantly eroded by post-impact earthquake aftershocks, making it a potentially intact archive of geological events that unfolded over the short-term.
"It's an expanded record of events that we were able to recover from within ground zero," said Gulick in a statement. "It tells us about impact processes from an eyewitness location."
In 2016, Gulick co-led the scientific drilling mission to the peak ring, which is submerged 450 meters below the Gulf of Mexico’s waters. The team extracted samples buried as deep as 1,300 meters into the seafloor while aboard a vessel called Liftboat Myrtle.
The cores revealed that the impact caused wildfires thousands of miles away, and produced a colossal tsunami that swept the remains of incinerated ecosystems back into the crater. The peak ring, which rose to an elevation of 425 feet in 24 hours, was partly built from the ashes of these scorched habitats.
“Within a day, a tsunami deposited material from distant shorelines, including charcoal,” the team writes in the study. “Charcoal likely originated from impact-related combustion of forested landscapes surrounding the Gulf of Mexico, as the impact site was entirely marine.”
If you were a dinosaur hanging around the nearby shoreline, you might have been set on fire by the impact, then had your earthly remains flow hundreds of miles into the blast zone to be deposited on the seafloor.
While it sounds like a surreal way to die, this may have been one of the cleanest possible exits from the Cenozoic. At least the first round of fiery deaths avoided the darkening of the skies and cooling of the climate, likely caused by the release of huge quantities of sulfate aerosols.
To that point, Gulick’s team found hardly any sulfur-rich deposits at the impact site, which supports a theory that sulfuric material simply vaporized into the atmosphere when the asteroid hit. Countless lifeforms survived the deluges of water and fire, only to slowly perish in this punishing new global climate.
Gulick called the cooling phase “the real killer” in a statement. "The only way you get a global mass extinction like this is an atmospheric effect," he said.
In other words, the first day of the Cenozoic era was also the worst day for its lifeforms, even if they weren’t snuffed out right away. The silver lining is that a play-by-play of that utterly ruinous 24 hours, and the hard times that followed it, survive on in the geological record.