Sometime in the Middle Eocene epoch, nearly 50 million years ago, a large object hurtled through Earth’s atmosphere, crashing into the North Sea between what’s now Britain and northwestern Europe.
The impact formed a crater 1 kilometer (about half a mile) deep and 3 kilometers wide. A plume of debris and water blasted skyward before falling back down, triggering a monster tsunami.
These are the findings of a new study, in which researchers attempt to settle a decades-long dispute over the origins of the Silverpit Crater, now buried 700 meters beneath the seabed about 130 kilometers off the southeastern coast of Great Britain.
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“Our evidence shows that a 160-meter-wide asteroid hit the seabed at a low angle from the west,” says first author Uisdean Nicholson, a geoscientist at Heriot-Watt University in Scotland.
“Within minutes, it created a 1.5-kilometer-high curtain of rock and water that then collapsed into the sea, creating a tsunami over 100 meters high,” he adds.
Discovered in 2002 using 3D seismic data, the crater is at the center of a long-running scientific debate about its formation. Scientists originally described it as a “hypervelocity impact structure,” citing its orientation within the circular fault zone as well as its own circular shape and central peak, all features consistent with high-speed impacts.
Yet it’s rare to find impact craters like this, as Nicholson acknowledges, and some researchers prefer other explanations. According to competing theories, the crater may have been formed from below, either due to subsurface salt movements or volcanic activity.
When the issue came to a vote at a 2009 geology debate, those present voted overwhelmingly in favor of the non-celestial origin, leading many to consider the issue settled.
Yet using multiple lines of evidence, including novel imaging capabilities, the new study makes a compelling case otherwise.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>“New seismic imaging has given us an unprecedented look at the crater,” Nicholson says. “Samples from an oil well in the area also revealed rare ‘shocked’ quartz and feldspar crystals at the same depth as the crater floor.”
Finding these shocked crystals was key to solving the case, he explains.
“We were exceptionally lucky to find these – a real ‘needle-in-a-haystack’ effort,” Nicholson says. “These prove the impact crater hypothesis beyond doubt, because they have a fabric that can only be created by extreme shock pressures.”
The findings seem to vindicate co-author Gareth Collins, a professor of planetary science at Imperial College London who was at the 2009 debate and has long supported the impact scenario.
“I always thought that the impact hypothesis was the simplest explanation and most consistent with the observations,” Collins says.
“It is very rewarding to have finally found the silver bullet,” he adds. “We can now get on with the exciting job of using the amazing new data to learn more about how impacts shape planets below the surface, which is really hard to do on other planets.”
Only about 200 terrestrial impact craters have been confirmed on our planet, and it’s even rarer to verify one at sea, where just 30 or so are agreed upon.
“Silverpit is a rare and exceptionally preserved hypervelocity impact crater,” Nicholson says. “These are rare because the Earth is such a dynamic planet – plate tectonics and erosion destroy almost all traces of most of these events.”
By shedding new light on this ancient calamity, the researchers hope to both understand Earth’s history and help prepare humanity for the next big one.
“We can use these findings to understand how asteroid impacts shaped our planet throughout history,” Nicholson says, “as well as predict what could happen should we have an asteroid collision in the future.”
The study was published in Nature Communications.