Approximately 35.65 million years ago, Earth experienced two massive asteroid impacts that left behind two of the planet’s largest known craters. Despite the significant size of these impacts, a study by researchers at University College London (UCL) has revealed that they did not lead to any lasting changes in the Earth’s climate. This finding sheds light on Earth’s remarkable resilience to certain catastrophic events, distinguishing it from other asteroid impacts that have profoundly shaped the planet’s history.
The impacts occurred roughly 25,000 years apart, resulting in the creation of the Popigai crater in Siberia, Russia, and the Chesapeake Bay crater in the United States. The Popigai crater spans about 60 miles (100 kilometers) in diameter, making it the fourth-largest known impact site on Earth, while the Chesapeake Bay crater measures between 25 and 55 miles (40 and 85 kilometers) across. The asteroids responsible were several miles wide, with the larger asteroid creating the Popigai crater estimated to be around 3 to 5 miles (5 to 8 kilometers) in diameter—roughly the height of Mount Everest.
The study, published in the journal Communications Earth & Environment, utilized advanced methods to reconstruct Earth’s climate in the 150,000 years following these impacts. Researchers analyzed isotopes in the fossils of microscopic, shelled organisms known as foraminifera, which lived in the ocean during that time. These isotopes, preserved in the creatures’ shells, provide a record of ocean temperatures when the organisms were alive. The analysis revealed no evidence of significant long-term climate shifts caused by the asteroid impacts, challenging earlier theories that linked such events to dramatic global climate changes.
Professor Bridget Wade, a co-author of the study from UCL’s Department of Earth Sciences, highlighted the surprising stability of Earth’s climate following the impacts. She explained that the team had anticipated a noticeable shift in isotope patterns, signaling either warming or cooling in the oceans, but no such change was detected. “These large asteroid impacts occurred, and over the long term, our planet seemed to carry on as usual,” she noted. However, she emphasized that the study’s resolution, with samples analyzed at intervals of approximately 11,000 years, would not capture shorter-term climatic changes lasting tens or hundreds of years.
While the long-term effects on climate were negligible, the immediate aftermath of these asteroid impacts would have been catastrophic by human standards. Such events generate massive shockwaves, trigger tsunamis, and release vast amounts of dust into the atmosphere. This dust can block sunlight, leading to temporary cooling and other environmental disturbances. For comparison, modeling studies of the Chicxulub impact—which caused the mass extinction event that wiped out the dinosaurs 66 million years ago—suggested significant short-term climatic effects lasting less than 25 years.
The UCL study involved analyzing over 1,500 foraminifera fossils, representing species that lived both near the ocean’s surface (planktonic foraminifera) and on the seafloor (benthic foraminifera). These fossils were extracted from a rock core collected beneath the Gulf of Mexico during the scientific Deep Sea Drilling Project. By examining both surface and deep-sea species, the researchers could construct a more comprehensive picture of oceanic conditions before, during, and after the asteroid impacts.
In their analysis, the researchers observed slight shifts in isotope patterns approximately 100,000 years before the impacts, suggesting a period of warming in the surface ocean by about 2 degrees Celsius and cooling in deep waters by about 1 degree Celsius. However, no notable isotopic changes were found corresponding to the time of the asteroid impacts or the subsequent 150,000 years. This absence of significant climatic shifts suggests that the Earth’s systems recovered relatively quickly from these events, maintaining long-term stability.
The study also identified physical evidence of the asteroid impacts in the form of tiny glass droplets known as microtektites. These droplets are created when an asteroid vaporizes silica-rich rocks upon impact. The vaporized material is ejected into the atmosphere, where it rapidly cools and solidifies into small glassy spheres. Thousands of these droplets were found within the rock core, confirming the occurrence of the two major impacts.
Interestingly, this period of Earth’s history, known as the late Eocene epoch, appears to have been marked by an unusually high frequency of asteroid impacts. In addition to the two major events, evidence points to at least three smaller impacts during the same timeframe. This suggests a possible disturbance in the solar system’s asteroid belt, although the exact cause remains unclear.
Previous studies on late Eocene climate and asteroid impacts had yielded conflicting results. Some researchers proposed that these impacts accelerated global cooling, while others suggested episodes of warming. However, many of these earlier studies relied on lower-resolution data, analyzing samples collected at greater intervals than 11,000 years and often focusing only on benthic foraminifera. The UCL study’s broader approach, incorporating fossils from multiple ocean depths and species, provides a more nuanced understanding of the climate during this period.
Natalie Cheng, an MSc Geosciences graduate and co-author of the study, reflected on the unexpected 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 sizable 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.”
Cheng also emphasized the importance of studying Earth’s past to better prepare for future threats: “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 underscores the resilience of Earth’s climate system but also highlights the need for vigilance regarding asteroid impacts. Even if the long-term climatic effects are minimal, the immediate consequences of a large asteroid impact—such as destruction, fires, and tsunamis—pose significant risks to life and infrastructure. Professor Wade called for continued investment in missions aimed at detecting and preventing future asteroid collisions, stressing the importance of preparedness in safeguarding the planet.
Source: University College London