A team led by Dr. Uisdean Nicholson of Heriot-Watt University in Edinburgh has concluded that the Silverpit Crater, buried under the southern North Sea, was carved out by an asteroid or comet striking the seabed between roughly 43 and 46 million years ago, according to Science Daily. The findings, published in Nature Communications, end a debate that has run since the structure was first identified in 2002. Science Daily reports that the collision sent up a curtain of rock and water and generated a tsunami estimated at more than 100 meters, or about 330 feet, high.
Why it matters
Silverpit now counts among the small number of impact craters on Earth whose cosmic origin has been confirmed, Science Daily reports. The site sits about 700 meters below the seabed in the southern North Sea, roughly 80 miles off the Yorkshire coast of England. The crater spans about three kilometers, and a far wider zone of circular faults, some 20 kilometers across, surrounds it.
For more than two decades, geologists argued over what produced the formation. Some held that underground salt movement had deformed the overlying rock into a crater-like shape. Others proposed that volcanic activity caused part of the seabed to collapse. In 2009, geologists even held a vote on the competing explanations, as documented in Geoscientist magazine, and most participants rejected the asteroid hypothesis, according to Science Daily.
The evidence that settled the question
The turning point came from two lines of evidence. The first was improved seismic imaging, which maps buried structures by tracking how sound waves move through different rock layers and can expose faults and craters that are otherwise invisible. Nicholson and his colleagues used the new data to study Silverpit's internal architecture in greater detail than before.
The decisive material, however, came from rock cuttings taken from an oil well near the crater. Within those samples, at the same depth as the crater floor, the researchers found quartz and feldspar crystals that had been "shocked" — minerals whose internal structure had been altered by extreme pressure. Nicholson described the find as a "needle-in-a-haystack" piece of luck and said the crystals prove the impact hypothesis beyond doubt, because their fabric can only arise under extraordinary shock pressures, Science Daily reports.
Such microscopic damage is not something ordinary geological processes are known to produce. Its presence at the crater floor gives physical backing to what the shape of the structure had long suggested: a nearly circular outline, a raised central peak, and rings of faults, all features seen at other confirmed impact sites. Central peaks form when rock compressed by a violent collision rebounds upward, in much the way water rises in the middle after something splashes into a pool.
Reconstructing the strike
With the origin established, the team turned to computer simulations built on physical laws to model the event. According to Science Daily, the models indicate an asteroid about 160 meters wide came in from the west and hit the seabed at a shallow angle. That is far smaller than the object linked to the extinction of the dinosaurs, but at cosmic velocity even a body of that size carries enormous energy.
The simulations suggest the impact threw up a curtain of debris and water roughly 1.5 kilometers high, which then fell back into the sea and produced a tsunami over 100 meters tall. In Nicholson's words, as reported by Science Daily, the asteroid struck at a low angle from the west and within minutes created that towering curtain, which collapsed into the ocean and drove the wave. Put another way, material was launched close to a mile into the air before crashing back down, and the resulting wave would have stood taller than a 30-story building.
That height figure comes from modeling rather than direct measurement, Science Daily notes. Even so, the reconstruction shows how much damage a comparatively modest asteroid can do when it lands in water. Tsunamis differ from ordinary wind-driven waves in that they involve the displacement of vast volumes of water, typically set off by a sudden disturbance such as an earthquake, an underwater landslide, or an impact.
For Professor Gareth Collins of Imperial College London, the result closes out a controversy he saw unfold at first hand; he took part in the 2009 vote, according to Science Daily.
The next step will be watching how the wider research community absorbs the result, and whether the same combination of high-resolution seismic imaging and microscopic mineral analysis is applied to other disputed buried structures.
