Silverpit Crater mystery solved: Asteroid crashed into the North Sea 43 million years ago

For more than 20 years, the Silverpit Crater deep under the North Sea has been the center of a heated scientific controversy. Some geologists were adamant that an asteroid produced the nearly-perfect circle hole, whereas others thought it was a result of more sluggish forces like migrating salt deposits or volcanic collapse.

Now, with high-tech seismic imaging, microscopic analysis of the minerals, and sophisticated computer simulations, the case is finally closed. Silverpit was formed by a catastrophic asteroid impact 43 to 46 million years ago.

Impact craters are a rarity on Earth. They only exist in about 200 places, and only 33 of them lie beneath the oceans, even though more than two-thirds of the planet is covered by water. The reason is simple: time devours them. Wind and rain break down craters on land, and oceanic craters are buried by sedimentation. So, Silverpit is a rarity in the geological world.

The 3.2-kilometer-diameter crater is 700 meters below the ocean floor, about 80 miles off the coast of Yorkshire. When first seen in 2002 on oil firm seismic surveys, its round shape and concentric faults thrilled.

Early study implied an asteroid impact, but evidence was thin. Without concrete proof, skeptics demanded more humdrum solutions. By 2009, skepticism had been so fierce that an open debate in the London Geological Society ended with the majority of the people voting against the impact hypothesis.

That skepticism was finally beginning to crumble in 2022, when the Northern Endurance Partnership carried out a collossal 3D seismic survey of the region. This time, researchers had sharper images than ever before of what lies beneath the surface.

High-definition scans showed classic impact crater signatures: a central rise, concentric fault zones stretching 18 kilometers outward, an inner crater nested within the main cavity, and dozens of small pits spread around the site.

These secondary craters, about 150 meters across, are especially interesting. They were likely formed when chunks of rock flung up by the original blast fell back onto the seafloor. This type of feature is common on the Moon and Mars but is effectively never preserved on Earth because of erosion. Their preservation here makes Silverpit a unique natural record of the effects of an asteroid impact into a shallow sea.

Even the most open seismic scans are not enough alone to show an effect. The "smoking gun" would be the presence of shocked minerals—tiny structural units within crystals found only in the high pressures of an asteroid impact.

In an oil well cut from a nearby well, scientists found just that: quartz and feldspar grains bearing pockmarked planar deformation features indicative of pressures ranging from 10 to 13 gigapascals.

Dr. Uisdean Nicholson, of Heriot-Watt University in Edinburgh, who was responsible for the research, characterized the discovery as a "needle-in-a-haystack effort" that provided conclusive proof. "These prove the impact crater hypothesis beyond doubt, because they have a fabric that can only be produced by extreme shock pressures," he said.

To pinpoint when the collision occurred, scientists examined small fossils trapped in rocks in surrounding rock layers. These nannofossils—fossils of ancient plankton—are good time clocks in Earth's past. The presence of them dated the event unambiguously to the middle Eocene, between 43 and 46 million years ago, when the region that now is the North Sea was a shallow marine shelf.

Computer simulations filled in the rest of the story. The simulations calculate that a 160-meter-wide rocky asteroid impacted at scorching speed of 15 kilometers per second, or nearly 45,000 miles an hour. The impact excavated a crater a kilometer deep in 12 seconds. Within minutes, the hollow buckled inward to form the central uplift in the seismic record. Seawater rushed back in, forming a massive wall of water and rock that crashed back onto the shore in an estimated 100-meter or more high tsunami.

Imperial College London Professor Gareth Collins, who had previously voted against the impact theory, supplied the computer models used in the study. "I always thought the impact hypothesis was the explanation and fit the observations best," he said. "It is extremely satisfying to have finally found the silver bullet."

One of the most striking findings is the asteroid's trajectory. Faulting suggests that it struck at low angle from the west-northwest. Low-angle impacts produce asymmetric craters, and the seismic information confirms this expectation. It is another line of evidence that rules out the alternative theories once believed by skeptics.

Compared to such monsters as the Chicxulub crater in Mexico linked to dinosaurs' extinction, Silverpit was small. However, its impact would have been catastrophic on anything that lived in the region around it. Asteroids of 100 meters or more in diameter can enter Earth's atmosphere and create cataclysmic craters, and Silverpit shows what this catastrophe looks like in a shallow sea.

The discovery also highlights the fragility of Earth's impact record. Plate tectonics and erosion erase most records of past impacts. The survival of Silverpit, buried under mounds of cover sediment, affords scientists a rare chance to gain insight into the processes that asteroids use to reshape ocean environments.

Researchers believe that further drilling into the crater could potentially yield even more information, including cores of rock that capture the melted and shattered material that's behind. Those would be utilized to enhance ocean impact models and get a better grip on phenomena like the devolatilization of chalk that produced the bizarre textures in Silverpit's central uplift.

For now, judgment has been passed. After decades of debate, Silverpit stands among recognized impact craters on Earth, as one of the best-preserved of its kind.

Confirmation of Silverpit as an impact crater does more than solve a tidbit of geological mystery. It gives scientists a rarely seen look at how mid-size asteroids engage with shallow oceans, causing tsunamis and shaping sea floors.

The find sharpens models of what to expect from future impacts, so it's essential for studies on planetary defense.

From Silverpit, scientists can learn to better predict the dangers presented by near-Earth objects that may one day strike our planet.

Research findings are available online in the journal Nature Communications.

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