Dust and Soot Contributed to End-Cretaceous Mass Extinction

Dust and Soot Contributed to End-Cretaceous Mass Extinction

A team of researchers from the US, the UK and Australia has analyzed burn markers from the boundary of the impact site of the Chicxulub crater in the Yucatán Peninsula in the southern Gulf of Mexico and the surrounding ocean to determine what caused the impact winter, a prolonged period of cold and dark conditions.

The Chicxulub asteroid impact. Image credit: Victor Leshyk.

About 66 million years ago, a 12-km-diameter asteroid collided with the Yucatán carbonate platform of the southern Gulf of Mexico, formed the Chicxulub impact crater, and ultimately resulted in the end-Cretaceous mass extinction of 76% species, including the non-avian dinosaurs.

The target rock was heated, vaporized, and ejected during the impact event. This released sulfate aerosols and dust, and possibly soot, into Earth’s upper atmosphere, which cooled and darkened the planet — a scenario known as an impact winter.

Organic burn markers are observed in end-Cretaceous boundary records globally, but their source is debated.

“The source of burn markers and whether they were caused by wildfires or rock carbon directly affects our understanding of the consequences of the impact that happened 66 million years ago,” said co-author Professor John Curtin, a researcher in the Western Australia Organic and Isotope Geochemistry Centre at Curtin University.

“When the impact occurred, the target rock was heated, vaporised and ejected, releasing sulphate aerosols, dust and possibly soot from the impact site.”

Professor Grice and colleagues were able to show that polycyclic aromatic hydrocarbons, together with these organic materials, initiated an impact winter and global darkening that caused the mass extinction.

“The cause of the burn markers has been debated for more than 30 years, as some researchers believed they were caused by wildfires which were ignited by the impact of the crash,” said first author Dr. Shelby Lyons, a scientist in the Department of Geosciences at the Pennsylvania State University.

“We instead found that the wildfires were less influential on immediate global climate and mass extinction than previously suggested.”

The findings were published in the Proceedings of the National Academy of Sciences.

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Shelby L. Lyons et al. Organic matter from the Chicxulub crater exacerbated the K-Pg impact winter. PNAS, published online September 28, 2020; doi: 10.1073/pnas.2004596117

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