In a rare finding made while searching for gas and oil, scientists have discovered a crater beneath the floor of the North Sea they believe was caused by an asteroid impact between 60 million and 65 million years ago.
Fewer than a dozen such craters have been found, and this one has yielded one of the most intricate 3-D maps of any terrestrial impact crater, researchers say. The data should provide clues to what happens when space rocks hit Earth.
Impact craters are often not visible on Earth's surface, because over time older ones are folded into the planet by shifting tectonic plates. In more recent times, craters such as the 45,000-year-old Barringer Crater in Arizona that are plainly visible, are heavily eroded by wind and rain.
The newfound structure, named Silverpit, is centered about 80 miles (130 km) off the east coast of Britain near the Humber estuary, which is north of London and near Hull.
Importantly, the impact appears to have occurred in shallow water, researchers say, and so the crater was rapidly buried after its formation and therefore largely preserved. It is now hidden under a few hundred yards (meters) of sediment at the bottom of a 130-foot-deep (40-meter) sea. It's shape and implications will be discussed in the Aug. 1 issue of the journal Nature.
The Silverpit crater is about 12 miles (20 km) wide. At its core are a central peak and a bowl shaped crater about 2 miles (3 km) across.
Radiating out from the core are at least 10 concentric rings, ridges that rise up to 16 stories above the crater floor. Experts had thought such rings only came with craters more than 10 times larger than Silverpit. How they could have formed in this case is now a matter for theorists to contemplate.
Simon Stewart, a geologist at British Petroleum and Phillip Allen of Production Geoscience, completed the study. They re-analyzed "seismic reflection data" that had been gathered in the early 1990s. The technique sorts out different densities of material, and so distinguishes between the crater's shapes and the overlying sediment.
Stewart is more than 90 percent sure the crater was caused by an impact.
"There's a very slim chance it could be some sort of volcanic explosion crater," Stewart told SPACE.com, "but it's sure got plenty geometrical characteristics of impact craters and none of volcanoes."
Assuming the crater was carved by an asteroid, or possibly a comet, Stewart estimates the rock would have been a bit wider than a football field is long. Collectively, objects like these are called meteors when they enter Earth's atmosphere.
"Water probably didn't slow the meteor much, because it weighed 2 million tons and was going 20 kilometers per second [44,740 mph]," Stewart said.
The dating of the crater - between 60 million and 65 million years ago - is based on the sedimentary rock layers that confine it and begs an interesting question: Could this asteroid that caused Silverpit have been a chunk that broke off the larger asteroid that hit the Yucatan Peninsula 65 million years ago? It is believe this event led to the demise of dinosaurs.
"That's an intriguing idea which we have elected to steer clear of" because of the imprecise dating -- the 5-million-year range of time -- for the Silverpit impact, Stewart said. "The implications of a fragmented dino-killer meteor are exciting though, not least because we would have to ask questions like, 'how many other big fragments are out there undiscovered in ocean basins?'"
For now, researchers will have to content themselves with a treasure trove of new data they can feed into computer models that predict how craters form during impacts.
Several research groups have built
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