Life recovered rapidly at impact site of dino-killing asteroid

Life bounced back within a decade in the crater left behind by the devastating asteroid that smashed into Earth about 66 million years ago and ended the reign of the dinosaurs along with 75 per cent of terrestrial life, scientists say. Researchers from the University of Texas in the US found that the crater was home to sea life less than a decade after impact, and it contained a thriving ecosystem within 30,000 years-a much quicker recovery than other sites around the globe.

The findings undermine a theory that recovery at sites closest to the crater is the slowest due to environmental contaminants, such as toxic metals, released by the impact. The evidence suggests that recovery around the world was influenced primarily by local factors, a finding that could have implications for environments rocked 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," said Lowery. The evidence for life comes primarily in the form of microfossils - the remains of unicellular organisms such as algae and plankton - as well as the burrows of larger organisms discovered in a rock extracted from the crater. The tiny fossils are hard evidence that organisms inhabited the crater, but also a general indicator about habitability in the environment years after impact.

The swift recovery suggests that other life forms aside from the microscopic were living in the crater shortly after impact. "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," he said.

The scientists found the first evidence for the appearance of life 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 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. The core containing the fossil evidence was extracted from the crater during a 2016 expedition. Scientists zeroed in on a unique core section that captures the post-impact seafloor in unprecedented detail.

While core samples from other parts of the ocean hold only millimetres of material deposited in the moments after impact, the section from the crater used in this study contains more than 130 metres 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 Timothy Bralower, a professor at Pennsylvania State University in the US. "We have a fossil record here where we're able to resolve daily, weekly, monthly, yearly changes," Bralower said.