Fossil microbes show how some life bounced back after dino-killing impact

SAN FRANCISCO — The first post-apocalypse tenants of ground zero of the dinosaur extinction didn’t waste much time moving in.

Drilling into the crater left by the dino-devastating Chicxulub impact in Mexico, researchers uncovered the fossilized remains of pioneering microbes. These “disaster species” colonized the harsh waters above the crater within hundreds of years of the impact, the researchers reported December 12 at a news conference at the American Geophysical Union’s fall meeting. The finding helps illuminate how life bounces back following cataclysmic events.

“This was a hostile, stressful environment for these organisms,” said Oleg Abramov, a planetary scientist at the Planetary Science Institute in Tucson, Ariz., who was not involved with the work. “It’s interesting that life came back so quickly to the site of the impact.”

The impact itself was one of the worst calamities in the history of life on Earth, releasing around 2 million times as much energy as the largest nuclear bomb ever detonated. It helped wipe out three-quarters of animal and plant species worldwide.

Not surprisingly, devastation was worst at the impact site, said Joanna Morgan, a geophysicist at Imperial College London who co-led the drilling project. Any life within around 1,500 kilometers of the impact site was probably fried with thermal radiation, she said.

Returning to the Chicxulub crater last April off the coast of the Yucatán Peninsula, Morgan and colleagues drilled into a now underwater ring of mountainous peaks that rises from the crater floor (SN Online: 11/17/16). Stacked on top of this peak ring are hundreds of meters of sediments laid down over the tens of millions of years since the crater formed. Fossils within these sediments offer a long-term history of life in the area.

Within hundreds of years of the impact, fossilized remains of two types of hardy plankton appear in the sediments. This is “at a time when the ocean is toxic and not very suitable for life,” said Timothy Bralower, a geoscientist at Penn State. The plankton, members of Thoracosphaera and Braarudosphaera, probably settled in the area to capitalize on the lack of competition. A third type of plankton from the same time period wasn’t an opportunist like the other two, but rather a native species that recolonized the area following the impact, Bralower said.

Analyzing Chicxulub rock samples for other signs of returning life continues. The impact generated hydrothermal systems in the ground that could have served as prime real estate for organisms that generate energy via chemical reactions, Abramov said. Similar impacts billions of years ago may have even fostered the emergence of life on Earth, he said.