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Life recovered rapidly at impact site of dino-killing asteroid

Posted May 31, 2018

About 66 million years ago, an asteroid smashed into the Earth triggering a mass extinction that ended the reign of the dinosaurs and snuffed out 75 percent of life.

While the asteroid killed off scores of species, a new study from Florida State University scientists, in collaboration with lead researchers from The University of Texas at Austin, has found that the crater it left behind was home to sea life less than a decade after impact, and contained a thriving ecosystem within 30,000 years — a much quicker recovery than other sites around the globe.

The three hair-covered forms (left) represent species of plankton found inside the crater. The geometric form (bottom left) is a species of algae. Small organisms like these moved into the crater so quickly that bones from animals that were killed by the impact, such as the mosasaur pictured here, may have still been visible. Image credit: Original art by John Maisano, University of Texas Jackson School of Geosciences.

“This study provides the first evidence that life, at least more simplistic organisms, recovered relatively quickly within the impact crater that marks the demise of the dinosaurs,” said Jeremy Owens, an assistant professor in Florida State’s Department of Earth, Ocean and Atmospheric Science and a member of the Geochemistry Group at the FSU-based National High Magnetic Field Laboratory, where he conducted measurements for the study.

The research was published in the journal Nature.

The findings challenge previous theories that recovery at sites closest to the crater — located partially offshore the Yucatan Peninsula in Mexico — were slowed by environmental contaminants 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 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 who led the research. “It shows that there’s not a lot of predictability of recovery in general.”

The evidence for life at the impact site comes primarily in the form of microfossils — the remains of unicellular organisms like algae and plankton — as well as the burrows of larger organisms discovered in a rock extracted from the crater. Samples were collected during recent scientific drilling conducted jointly by the International Ocean Discovery Program (IODP) and International Continental Drilling Program (ICDP).

The tiny fossils are hard evidence that organisms inhabited the crater, and they serve as a general indicator about habitability in the environment after the impact.

The scientists found signs that life first returned to the crater two to three years after impact. The evidence included burrows made by small shrimp or worms. By 30,000 years after impact, a thriving ecosystem was present in the crater with blooming phytoplankton (microscopic plants) supporting a diverse community of microfossils 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.

Owens said that rapidly restored oxygen levels found soon after impact could help explain the quick recovery in the region.

“Using geochemical tools, we discovered that local oxygen contents returned to high values immediately following the asteroid impact,” he said. “This suggests the area could have been re-inhabited by organisms requiring oxygen relatively quickly.”

The crater is filled with millions of years’ worth of rock and sediment — a feature that preserved the crater’s structure and allowed the international research team to extract more than 800 meters (2,600 feet) of core that has revealed information about the asteroid’s impact, aftermath and the recovery of life.

The relatively rapid rebound of life in the crater suggests that while the asteroid caused the extinction, it didn’t hamper recovery. The scientists point to local factors, from water circulation to interactions between organisms and the availability of ecological niches, as having the most influence on a particular ecosystem’s recovery rate.

Although life quickly returned to the crater, the ecosystem was significantly different after the impact. A few species that survived the mass extinction adapted to vacated habitats by evolving into new species that were better suited to the changing conditions. The findings illustrate that in the wake of mass extinction events, ecosystem recovery is an unpredictable process — both in timing and in species composition.

Source: Florida State University

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