A long-running debate about a mysterious crater hidden beneath the North Sea has finally been settled. Researchers have confirmed that the Silverpit Crater was created when an asteroid or comet slammed into the region roughly 43 to 46 million years ago.
The finding resolves a scientific argument that has lasted for more than two decades and identifies Silverpit as one of Earth’s relatively rare impact craters, geological scars left behind when space rocks strike the planet at tremendous speeds.
The research team, led by Dr. Uisdean Nicholson of Heriot-Watt University in Edinburgh and funded by the Natural Environment Research Council (NERC), combined advanced seismic imaging, microscopic analysis of rock samples, and computer simulations to build the strongest case yet for an extraterrestrial impact. Their results were published in the journal Nature Communications.
A Hidden Crater Beneath the North Sea
The Silverpit Crater lies about 700 meters (2,300 feet) beneath the floor of the southern North Sea, approximately 80 miles from the Yorkshire coast.
Since its discovery in 2002, the structure has puzzled geologists. The crater itself spans about three kilometers (1.9 miles) across and is surrounded by a much larger ring of circular faults extending roughly 20 kilometers (12 miles). Faults are fractures in rock layers that form when the Earth’s crust is stressed or displaced.
Many scientists believed Silverpit was created by a hypervelocity impact, the term used for collisions involving asteroids or comets traveling at several miles per second. The crater’s circular shape, central peak, and distinctive surrounding fault pattern resembled features seen at known impact sites around the world.
Not everyone agreed.
Some researchers proposed that the structure formed when underground salt deposits shifted over time. Others suggested it resulted from volcanic processes that caused part of the seabed to collapse.
The disagreement became so intense that geologists formally voted on the crater’s origin in 2009. According to a report in the December 2009 issue of Geoscientist magazine, most participants rejected the impact explanation.
The latest evidence now overturns that conclusion.
New Evidence Reveals an Ancient Asteroid Strike
To reexamine the mystery, scientists turned to newly available seismic data. Seismic imaging works somewhat like an ultrasound scan for the Earth, allowing researchers to create detailed pictures of underground rock layers using reflected sound waves.
The new images provided an unprecedented view of the crater’s internal structure.
The team also examined rock fragments collected from an oil exploration well near the site.
Dr. Uisdean Nicholson, a sedimentologist in Heriot-Watt University’s School of Energy, Geoscience, Infrastructure and Society, said: « New seismic imaging has given us an unprecedented look at the crater.
« Samples from an oil well in the area also revealed rare ‘shocked’ quartz and feldspar crystals at the same depth as the crater floor.
« We were exceptionally lucky to find these — a real ‘needle-in-a-haystack’ effort. These prove the impact crater hypothesis beyond doubt, because they have a fabric that can only be created by extreme shock pressures. »
Shocked minerals are considered some of the strongest evidence for an asteroid impact. The microscopic structures inside these crystals form only when rocks experience enormous pressures far beyond those produced by normal geological activity.
A 160-Meter Asteroid and a Towering Tsunami
Based on the team’s analysis, the object that struck the North Sea was about 160 meters (525 feet) wide and approached from the west at a shallow angle.
Although relatively small compared to the asteroid linked to the extinction of the dinosaurs, it was still large enough to unleash extraordinary destruction.
Dr. Nicholson said: « Our evidence shows that a 160-meter-wide asteroid hit the seabed at a low angle from the west.
« 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. »
A tsunami of that size would have towered more than 330 feet above sea level, higher than many modern skyscrapers.
The impact would have instantly excavated the crater while blasting huge volumes of rock, sediment, and seawater into the atmosphere.
The Search for the « Silver Bullet »
One of the researchers involved in the new study was Professor Gareth Collins of Imperial College London, who also attended the debate over Silverpit’s origin in 2009.
Collins developed the numerical models used to simulate the impact and compare its effects with the crater’s observed structure.
Professor Collins said: « I always thought that the impact hypothesis was the simplest explanation and most consistent with the observations.
« It is very rewarding to have finally found the silver bullet. 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. «
Why Impact Craters Are So Rare
Despite the countless asteroids and comets that have struck Earth throughout its history, surprisingly few impact craters remain visible today.
Earth’s surface is constantly being reshaped by erosion, weathering, volcanic activity, and the slow movement of tectonic plates. Over millions of years, these processes erase many traces of ancient impacts.
Dr. Nicholson said, « Silverpit is a rare and exceptionally preserved hypervelocity impact crater.
« These are rare because the Earth is such a dynamic planet — plate tectonics and erosion destroy almost all traces of most of these events.
« Around 200 confirmed impact craters exist on land, and only about 33 have been identified beneath the ocean.
« We can use these findings to understand how asteroid impacts shaped our planet throughout history, as well as predict what could happen should we have an asteroid collision in future. »
Joining the Ranks of Famous Impact Craters
The confirmation of Silverpit’s origin places it among a select group of known impact structures.
These include Mexico’s Chicxulub Crater, which is widely linked to the mass extinction that wiped out the nonavian dinosaurs 66 million years ago, and the Nadir Crater off the coast of West Africa, another underwater impact site that was only recently confirmed.
With the debate finally resolved, scientists can now use Silverpit as a valuable natural laboratory for understanding how asteroid impacts affect both Earth and other worlds across the solar system.
The research was funded by the Natural Environment Research Council (NERC).
Source:
www.sciencedaily.com
