Public Release: 

Did the Chicxulub asteroid knock Earth's thermometer out of the ballpark?

American Association for the Advancement of Science

When the Chicxulub asteroid smashed into Earth 65 million years ago, the event drove an abrupt and long-lasting era of global warming, with a rapid temperature increase of 5°Celsius (C) that endured for roughly 100,000 years, a new study reports. The monumental event is a rare case where Earth's systems were perturbed at a rate greater than what's occurring now from human activity. It therefore provides valuable insights into what may happen from sudden, extreme environmental changes. The aftereffects of the Chicxulub impact remain debated, with some scientists advocating that soot within the atmosphere blocked out the sun sufficiently to drive global cooling; others suggest that carbon released from the Earth's crust into the atmosphere upon the asteroid's impact, as well as carbon from wildfires, had a warming effect. To better understand how the temperature changed during this time, Ken MacLeod and colleagues analyzed a robust collection of well-preserved, sand grain-sized remains of fish teeth, scales and bone from a site in Tunisia; these samples retain oxygen isotopic signatures that reveal the temperature at the time that the related animal was alive. The authors were able to collect samples from sediments that span the time leading up to the Chicxulub impact, until long afterwards. Based on their analysis, they propose that global temperatures increased by about 5°C and did not cool to previous values for roughly 100,000 years after the impact, a magnitude and duration of warming closely matching levels of carbon dioxide that some types of analyses have estimated were emitted during the same period. MacLeod et al. do note some discrepancy between their results and concentrations of atmospheric carbon dioxide derived from other kinds of analyses, which predict a more modest increase.

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