The news went around the world, when a Danish and international research team led by Kurt Kjær at the Globe institute at University of Copenhagen published their discovery of a new, large impact crater in northwest Greenland in November 2018. The 31-km wide structure is buried under the Greenland Ice Sheet behind a glacier named Hiawatha. Therefore, this also became the name of the crater. The scientists found that the crater must be very young, seen from a geological perspective, but not precisely how young.
Now, a new study published in Geology from the group reveals that the crater must almost certainly be younger than 3 million years old, which makes it the youngest of Earth’s 25 large impact craters.
Adam Garde, the first author of the new study and emeritus scientist at the Geological Survey of Denmark and Greenland (GEUS), explains that ”The cellular structures of the charred wood that we recovered in outwash from the hidden crater contained an unexpected clue to the young age of the impact.”
Exploded wood cells
According to Adam Garde, ”The maximum age of the Hiawatha crater was determined in a rather untraditional way”, but this was also quite elegant.
”One of my coauthors Jette Dahl-Møller and I investigated the cell structures in the charred wood under the microscope. We could see that some of the bark cells were full of large, spherical voids and had been greatly expanded, as if the fatty material in these cells had been vaporized by extreme and rapid heating”.
”We also found many small grains of shock-melted glass, which both contained fragments of shocked minerals and a lot of finely dispersed organic material. This could not have been incorporated into the glass unless is also itself had been shocked, disintegrated and mixed with the molten rock from the impact”.
With support from other types of analysis of the organic material, the scientists were eventually convinced that the charred wood stemmed from the impact and not from natural wildfires, which could be an alternative explanation for the charring.