Ancient arctic splashdown.

Delving beneath the seafloor north of Scandinavia, geologists have discovered a large crater left by a meteorite impact roughly 130 million years ago. The crater and surrounding debris are among the best-preserved on Earth, reports a team of Norwegian and U.S. researchers in the September Geology.

The 40-kilometer-wide Mjolnir crater lies 400 meters below the surface of the Barents Sea. In 1993, researchers at the University of Oslo proposed that the crater had formed during an impact, but they lacked conclusive proof and could not determine its age. To resolve these issues, the scientists studied sediments drilled at a site 30 kilometers north of the crater.

There they discovered slivers of shocked quartz-grains with intersecting fractures caused by high-pressure shock waves. They also measured high concentrations of the element iridium in the sediments. Geologists regard both features as calling cards left by an extraterrestrial impact. The age of the sediments dates the crash to the latest part of the Jurassic or the earliest part of the Cretaceous period.