“This is the way science works and should work,” said Kurt Kjær, a geologist at the Natural History Museum of Denmark and codiscoverer of the Hiawatha Crater under the Greenland Ice Sheet. He and colleagues recently determined the crater is 58 million years old, far older than proponents of a controversial hypothesis had hoped (Science, March 11, 2022, p. 1076).

When the crater’s discovery was announced in 2018, the mere possibility that it could have been formed only a geologic eyeblink ago (say, around 12,800 years ago) and therefore could have caused a climate shift and extinction led to exuberant reporting (see Boslough, “Crater Discovery Story Flawed by Premature Link to Speculative Impact Hypothesis,” Skeptical Inquirer, March/April 2019).

Proponents of the Younger Dryas Boundary (YDB) impact hypothesis made bold predictions: “I’d unequivocally predict that this crater is the same age as the Younger Dryas,” pronounced James Kennett of the University of California, Santa Barbara (Science, November 14, 2018).

Subject matter experts were more circumspect. Christian Koeberl (University of Vienna) noted the lack of evidence: “There should be thick ejecta layers in all ice cores nearby. Yet there’s nothing” (Popular Science, November 16, 2018).

Clark Chapman (Southwest Research Institute) highlighted the improbability compared to something as old as two million years, noting that “It would be at least a hundred times less likely that it could have happened so recently as to have affected the Younger Dryas” (Science News for Students, January 2, 2019).

Greenland ice core and paleoclimate expert Richard Alley told me:

A few shards of glass from a volcanic eruption are enough to stop an ice-core processing line so the workers can take pictures, even getting selfies with it. Nothing showed up in any cores in the Younger Dryas. An impact near the coast that threw material up to Summit would have left chain-saw-dulling material at Pakitsoq near the coast, but nothing showed up.

Elizabeth Silber (Sandia National Laboratories, adjunct at the University of Western Ontario) published simulations of impacts into ice to see if a crater could have formed without leaving evidence in ice cores, despite only “occurring once every ∼2 million years.” Her models, under carefully specified conditions that assumed thick Pleistocene ice, couldn’t rule out a young age (< 2.6 million years; see ArXiv:20-4:07909). She acknowledged the physical possibility of an improbably young crater. Now, after coauthoring the confirmation of its ancient age, she told me, “Our modelling results indeed support the slow erosional rates and are consistent with the crater being millions of years old.”

YDB impact enthusiasts, who had argued that their hypothesis should be promoted to a “theory,” were disappointed. Devotees had considered the Hiawatha Crater their smoking gun despite expert opinion. Their hopes now hinge primarily on their own definition of impact markers that contradicts longstanding mineralogic and geochemical criteria established by impact specialists (Jaret and Harris, Nature Scientific Reports, March 25, 2022).

Responding to the new paper, Kennett said, “I don’t think it’s related to the Younger Dryas now.” But he says the team still believes in their impact hypothesis and will continue to do research on what they still think is impact evidence. “It’s all alive and well and very active” (Science, March 11, 2022).