The Hiawatha crater in western Greenland, previously estimated to be very small, formed long before the island glaciation. This is the result of detailed isotope studies on sands and minerals by a team led by Gavin G. Kenny of the Swedish Museum of Natural History in Stockholm. As stated by the working group in “Science Advances”, resetting the primary and isotopic ratios of the samples used as a “geological clock” to zero occurred 58 million years ago. At the same time, zircons with a low content of uranium and lead show characteristic damage to the crystal lattice, which may be caused by the intense shock wave of an asteroid impact. Experts conclude that the crater was formed long before the current Ice Age.
The crater finders, a working group led by Kurt H. Keir of the Museum of Natural History in Copenhagen, An amazing hypothesis came up in 2018. Less than three million years ago, during the Pleistocene, a kilometer-sized asteroid crashed into the Greenland ice sheet – in the very recent geological past. The 31-kilometer crater that covers the channels under the ice has not eroded. Radar data from the ice itself showed that the ice sheet and the crater had not yet equilibrated, and Danish experts believed they could identify signs of residual heat in the once-melt rocks from the impact.
However, even then there were some inconsistencies. Such a recent impact would have left a thick, easily identifiable blanket of debris throughout the area. In addition, an asteroid of this size would have had dramatic effects on the climate – and Ice Age climate is well known from the ice core, among other things. Data from Kenny’s team now elegantly resolves the contradiction: the effect is much older. Rather than hitting a kilometer-thick ice sheet, it would likely have hit lush subtropical forests, because 58 million years ago the Earth was still in a hot period.
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