Seriously, it is really cool to see Science Magazine name Hiawatha Crater as 2018 breakthrough story runner up — and with due reference to the Younger Dryas Impact Hypothesis. The crater will be an intellectual gift that keeps on giving, and its better days are ahead. So I will go ahead and nominate the article “Hiawatha crater dates to start of the Younger Dryas” as THE Science story for 2020, or, who knows, maybe 2019.
The asteroid slammed into northwestern Greenland like a fusillade of nuclear bombs, instantly vaporizing rock and sending shock waves across the Arctic. The scar it left—a 31-kilometer-wide impact crater called Hiawatha—is big enough to hold Washington, D.C. Scientists reported the startling discovery in November, after aircraft radar revealed the crater lurking beneath the kilometer-thick ice sheet.
Hiawatha crater is one of the 25 largest on Earth. Though not as cataclysmic as the dinosaur-killing Chicxulub impact, which carved out a 200-kilometer-wide crater in Mexico 66 million years ago, the Hiawatha impact could have had a powerful effect on the global climate. Meltwater from the impact, pouring into the north Atlantic Ocean, could have sent temperatures plunging by halting a conveyor belt of currents that brings warmth to northwest Europe.
The radar images suggest Hiawatha is exceptionally fresh, dating from the past 100,000 years. And a disturbance in the crater’s deep ice hints that the asteroid may have struck as recently as 13,000 years ago. That would tie the impact to the Younger Dryas, a thousand-year global cooling event that began just as the world was thawing from the last ice age. It would also vindicate proponents of the controversial Younger Dryas impact theory. A decade ago, they proposed that extraterrestrial impacts could account for hints of mayhem in the archaeological and geological record. But they could never point to a crater.
The timing of this impact is far from settled. Ice cores elsewhere on Greenland, which record the past 100,000 years, contain no signs of impact debris. A firm answer will depend on painstaking work to tease dates from the radioactive clocks in tiny mineral crystals swept from under the ice.
If they show the Hiawatha impact did occur 13,000 years ago, it would have come just as humans were fanning across a new continent, chasing mastodons around North America. It is tempting to imagine their thoughts as they looked up to see the searing white orb of the impactor, four times brighter than the sun. —Eric Hand