Around 66 million years ago, an asteroid now known as the Chicxulub impactor, struck the Earth’s surface leaving a crater 93 miles in diameter. This impact is widely agreed to have caused 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.
Although the asteroid killed off such a high percentage of Earth’s species at the time, new research led by The University of Texas at Austin has found that the crater it left behind was home to marine life less than a decade after impact, and it contained a thriving ecosystem within 30,000 years, a much quicker recovery than other asteroid impact sites around the globe.
These findings undermine a theory that species recovery at sites closest to the crater is the slowest due to environmental contaminants, such as toxic metals, released by the impact. Instead, the evidence suggests that recovery around the world was influenced primarily by local factors, a finding that could have implications for marine environments affected by climate change today.
“We found life in the crater within a few years of impact, which is really fast, surprisingly fast,” said Chris Lowery, a postdoctoral researcher at the University of Texas Institute for Geophysics (UTIG) who led the research. “It shows that there’s not a lot of predictability of recovery in general.“
The scientists found the first evidence for the appearance of life two to three years after impact, in the form of microfossils discovered in rock extracted from the crater during recent scientific drilling conducted jointly by the International Ocean Discovery Program and International Continental Drilling Program. The evidence also included fossilised burrows made by small shrimp or worms. By 30,000 years after impact, a thriving ecosystem was present in the crater, with blooming phytoplankton supporting a diverse community of organisms in the surface waters and on the seafloor. In contrast, other areas around the world, including the North Atlantic and other areas of the Gulf of Mexico, took up to 300,000 years to recover in a similar manner.
“Microfossils let you get at this complete community picture of what’s going on,” Lowery said. “You get a chunk of rock and there’s thousands of microfossils there, so we can look at changes in the population with a really high degree of confidence … and we can use that as kind of a proxy for the larger scale organisms.”
The core containing the fossil evidence was extracted from the crater during a 2016 expedition co-led by the Jackson School. In this study, scientists zeroed in on a unique core section that captures the post-impact seafloor in unprecedented detail. Whereas core samples from other parts of the ocean hold only millimeters of material deposited in the moments after impact, the section from the crater used in this study contains more than 130 meters of such material, the upper 30 inches of which settled out slowly from the turbid water. This material provides a record that captures the seafloor environment days to years after the impact.
“You can see layering in this core, while in others, they’re generally mixed, meaning that the record of fossils and materials is all churned up, and you can’t resolve tiny time intervals,” said co-author Timothy Bralower, a micropaleontology professor at Pennsylvania State University. “We have a fossil record here where we’re able to resolve daily, weekly, monthly, yearly changes.”
The team’s findings indicate that recovery after a global catastrophe could vary between ecosystem localities, with influencing factors including water circulation, interactions between organisms and the availability of ecological niches.
Christopher M. Lowery, Timothy J. Bralower, Jeremy D. Owens, Francisco J. Rodríguez-Tovar, Heather Jones, Jan Smit, Michael T. Whalen, Phillipe Claeys, Kenneth Farley, Sean P. S. Gulick, Joanna V. Morgan, Sophie Green, Elise Chenot, Gail L. Christeson, Charles S. Cockell, Marco J. L. Coolen, Ludovic Ferrière, Catalina Gebhardt, Kazuhisa Goto, David A. Kring, Johanna Lofi, Rubén Ocampo-Torres, Ligia Perez-Cruz, Annemarie E. Pickersgill, Michael H. Poelchau, Auriol S. P. Rae, Cornelia Rasmussen, Mario Rebolledo-Vieyra, Ulrich Riller, Honami Sato, Sonia M. Tikoo, Naotaka Tomioka, Jaime Urrutia-Fucugauchi, Johan Vellekoop, Axel Wittmann, Long Xiao, Kosei E. Yamaguchi, William Zylberman. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction. Nature, 2018; DOI: 10.1038/s41586-018-0163-6
Location of where the Chicxulub asteroid struck the Earth, on Mexico’s Yucatan Peninsula. Credit: NASA