The asteroids struck Earth about 25,000 years apart during the late Eocene epoch. The larger of the two created the 60-mile-wide (100km) Popigai crater, while the other left a 25-55 mile-wide (40-85km) impact in Chesapeake Bay. These craters are the fourth and fifth largest known asteroid craters on Earth.
The study, published in Communications Earth and Environment, analyzed climate conditions in the 150,000 years surrounding these impacts. Using isotopic analysis of fossils from tiny, shelled marine organisms known as foraminifera, researchers reconstructed past ocean temperatures.
"What is remarkable about our results is that there was no real change following the impacts," said Professor Bridget Wade of UCL Earth Sciences. "We expected the isotopes to shift in one direction or another, indicating warmer or cooler waters, but this did not happen. These large asteroid impacts occurred and, over the long term, our planet seemed to carry on as usual."
Professor Wade emphasized, however, that the study's methodology could not capture shorter-term climate effects lasting decades or centuries. "Over a human time scale, these asteroid impacts would be a disaster," she added, describing immediate consequences such as shockwaves, tsunamis, and atmospheric dust blocking sunlight.
The study team examined over 1,500 fossils from both surface-dwelling (planktonic) and seafloor-dwelling (benthic) foraminifera. These specimens were extracted from a rock core drilled beneath the Gulf of Mexico as part of the Deep Sea Drilling Project.
Researchers also noted evidence of asteroid activity in the form of thousands of tiny silica glass droplets embedded in the rock, formed when the heat of impact vaporized silica-containing rocks. These droplets later solidified in the atmosphere before falling back to Earth.
The findings challenge prior studies, which suggested asteroid impacts during the late Eocene may have caused significant climatic shifts. Earlier analyses, conducted with lower-resolution sampling and narrower data scopes, had been inconclusive, with some studies linking the impacts to periods of cooling or warming.
Co-author and MSc Geosciences graduate Natalie Cheng expressed surprise at the findings. "Given that the Chicxulub impact likely led to a major extinction event, we were curious to investigate whether what appeared as a series of sizeable asteroid impacts during the Eocene also caused long-lasting climate changes. We were surprised to discover that there were no significant climate responses to these impacts."
She added, "It was fascinating to read Earth's climate history from the chemistry preserved in microfossils. It was especially interesting to work with our selection of foraminifera species and discover beautiful specimens of microspherules along the way."
The study also detected a modest warming of about 2 C in surface waters and a 1 C cooling in deep waters approximately 100,000 years before the impacts. However, no temperature changes were observed around or after the asteroid strikes.
This research underscores the importance of continued monitoring and preparation for future asteroid threats, Wade noted. "We still need to know what is coming and fund missions to prevent future collisions."
Research Report:No paleoclimatic anomalies are associated with the late Eocene extraterrestrial impact events
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