Some 66 million years ago, when a roughly 12-kilometer-wide asteroid slammed into a shallow reef near the present-day Yucatan Peninsula, the impact drilled a crater kilometers deep, vaporized the surrounding ocean, and piled up mountains of rebounding material inside the crater, which filled again with water. The crash also sterilized the immediate area down to the tiniest forms of life and is thought to have wiped out all nonavian dinosaurs around the globe.
It would have been impossible for life to survive on the surface near the impact, say researchers. Consequently, they have long wondered how soon after the crash might marine life, which had been relatively protected in the water, have secured a toehold once again in the devastated region.
Now Chris Lowery, a paleoceanographer at the Institute for Geophysics at the University of Texas at Austin, and his collaborators have shown that marine life started to return to the region within approximately 30,000 years, a relatively quick recovery on geological timescales. The team determined the timing from samples of rock extracted from the crater, known as Chicxulub, named after a nearby town in Mexico. They also investigated how marine life-forms adapted to their new environment.
There’s been a lot of research looking at how life has returned far from Chicxulub at sites around the world, Jaime Urrutia Fucugauchi, a geophysicist at the National Autonomous University of Mexico in Mexico City, told Eos. However, this investigation “is looking directly in the target zone,” he said. Urrutia Fucugauchi was not involved in Lowery’s study.
A Rare Crater
Today, Chicxulub is partially submerged in the Gulf of Mexico. It’s one of the best-preserved large impact craters on Earth and the only one linked to a major extinction, which makes it an excellent test bed for studying the return of life after an impact, said geophysicist Sean Gulick, also at the University of Texas at Austin.
In 2016, an international team of researchers led by Gulick and Joanna Morgan, a geophysicist at Imperial College London, extracted a sedimentary core from Chicxulub using a three-legged drilling rig. The team sampled the crater’s peak ring, material uplifted by over a hundred meters relative to the crater floor. Peak rings are hallmarks of large impacts throughout the solar system—they’ve been spotted on Mercury, Venus, Mars, and the Moon—but nonetheless remain poorly understood.
Tiny Marine Creatures
The new core samples were extracted from roughly 506 to 1,335 meters below the seafloor, and Lowery and his colleagues focused on sediment collected from roughly 617 meters below the seafloor, corresponding to material laid down immediately after the asteroid impact.
With the goal of investigating how life returned after the cataclysm, Lowery and his team focused on plankton and foraminifera, tiny shelled marine creatures. The scientists studied preserved foraminifera shells found within the core and burrows created by animals that were not themselves preserved.
The researchers found that foraminifera and plankton populations reappeared within the impact crater within a few tens of thousands of years. “Within about 30,000 years of the impact…there’s a diverse assemblage of plankton,” said Lowery. “It looks like a healthy ecosystem.”
He presented these results Tuesday at the American Geophysical Union’s 2017 Fall Meeting in New Orleans, La.
Foraminifera and plankton living in the postimpact environment also developed unique adaptions, Lowery reported. For instance, some foraminifera developed spines for the first time, an adaptation that allowed them to gather food more effectively. “Spines provided structure and strength so that [these creatures] could hold on to things and eat them,” said Lowery. These new attributes were an evolutionary response to competition for scarce food, he said, which likely resulted from changes in nutrients in the water after the impact. “The zooplankton diversify really quickly because they’ve got to compete with one another for food,” he explained.
Lowery said that next, he and his team will be studying how Earth’s climate evolved during the Paleocene, the roughly 10-million-year epoch following the impact. The researchers will be looking at a period of warming that Lowery calls the “best analog” for the modern-day warming the planet is now experiencing. “We’ve got this great [ancient] greenhouse world in the Gulf of Mexico that we can study,” he said.