If you travel 140 miles southeast of Kiev, Ukraine, just before you reach the tiny village of Bukvarka, you’ll arrive at a patch of forest that streaks across agricultural lands. The gently sloping meadows and cottages are bucolic, giving no indication of the area’s violent past. But burrow down 1,700 feet or so and you’ll find the remnants of a catastrophic impact: a 15 mile–wide asteroid crater.
Scientists say that about 65 million years ago an asteroid the length of three Eiffel Towers struck here, its fiery fallout blanketing an area the size of present-day Vermont. The impact dumped a colossal amount of heat into the ground—enough to melt rock and form a massive depression called the Boltysh crater, a hole now filled in by asteroid detritus and sediments of a lake long gone.
Previous studies have assigned the Boltysh impact event a broad range of dates to suggest that it may have coincided with the Chicxulub impact event—with the two asteroid strikes both contributing to the extinction of the dinosaurs. Now, a more precise follow-up study published today in Science Advances suggests the Boltysh impact occurred 650,000 years later than the Chicxulub impact, long after the dinosaurs disappeared. Though the Boltysh impact is no longer fingered in the famous mass extinction event, pinpointing the crater’s age has allowed scientists to correlate the asteroid strike to other global shake-ups of its time.
“You’re trying to document a major event that basically, surely shaped the biosphere and changed evolution of the Earth,” says Philippe Claeys, a geologist at the Free University of Brussels, Belgium who didn’t participate in the study. “You will need to understand every event taking place at that moment. Is it important to document an event like Boltysh? Absolutely.”
Annemarie Pickersgill, a geologist at the University of Glasgow, UK who led the research, dated the Boltysh crater by looking at the age of the sediments that had settled on top. These sediments came from the rocks that were melted by the asteroid impact and the soil that had accumulated over the millions of years since. Her team examined the cores drilled from this sedimentary pileup using a dating method that measures the accumulation a particular isotope of argon and estimated the crater’s age to be 65.39 million years.
“This is a really nice study,” says Claeys. “The argon ages are absolutely beautiful.”
The first attempts to date the Boltysh crater in the early 2000s involved the same dating method, albeit with lower precision due to technological limitations. Scientists estimated the impact occurred sometime during a span of 1.3 million years. The imprecise measurement left open the possibility that the Boltysh impact may have overlapped with Chicxulub’s fateful formation. This wide age range fertilized speculations that the Boltysh impactor, beating Chicxulub’s to Earth by a hair, acted as the first of a one-two punch that wiped out the dinosaurs. In the 18 years since the first study, dating techniques have improved to the extent that Pickersgill’s team could increase the measurement precision fourfold, disentangling Boltysh and Chicxulub once and for all. Their results confirm that the Boltysh has nothing to do with the extinction of the dinosaurs, because it happened much later. “If there's a burglary and then I arrived at the bank later, nobody's going to be like, ‘You were there, you did it,’” says Pickersgill.
The Boltysh impact may no longer be guilty of helping to cause the extinction of dinosaurs, but its new, more precise age puts it around a time of much climatic upheaval. Boltysh’s impactor made landfall right at the end of the Deccan Trap volcanism period, when volcanic seams in the earth split and spewed large amounts of greenhouse gases into the atmosphere. At this time of widespread volcanic activity, when the planet was still reeling from the impact event that formed the Chicxulub crater, a new hyperthermal event started—a period of extreme global warming during which ocean temperatures rose by nearly four degrees Fahrenheit. The new results from Pickersgill’s team make the Boltysh impact a suspect for kickstarting the hydrothermal event.
Normally, an asteroid the size of Boltysh’s impactor—ten times smaller than the infamous rock that formed Chicxulub—would be too puny to cause damage on a global scale. Nevertheless, the impactor may have triggered a series of unfortunate events because the planet was already in a fragile state.
“A question we posed was, when [Earth] was already stressed, was it possible that a small impact could have pushed things over the edge for a hyperthermal?” says Pickersgill.
The jury is still out, she says. The Boltysh crater’s age alone isn’t enough evidence to prove the asteroid’s guilt, and she can’t speculate on how an impact might have sparked subsequent events. More follow-up studies are needed, she says.
Sonia Tikoo, a geophysicist at Stanford University who wasn’t involved in the research, says she thinks that the Boltysh impactor was too small to have set off a global climate shift. Although the crater’s age is uncannily close to the hyperthermal event, “it's just a nice coincidence… but I'm not sure they're related,” she says. Still, the new study encourages scientists to think about how the sizes of asteroids and the target rocks they slam into perturb the climate. “It's inspiring us to dig into these questions a bit more deeply,” she says.
Earth is constantly peppered with celestial bodies, including larger visitors like Boltysh’s and Chicxulub’s impactors that hit every one to three million years. On geological timescales, asteroid events are not so freakish, and their craters are important records of Earth’s past. Boltysh might now have not played a role in the dinosaur extinction, but “it's another component of the entire story” of a much happening time, says Claeys.
Editors' Note, June 18, 2021: This article originally misspelled hyperthermal event. We regret the error.