Much earlier than thought: The huge Hiawatha crater under the Greenland ice was formed 58 million years ago and therefore not just when humans already existed, as previously assumed. This emerges from analyzes of rock material that was formed during the asteroid impact. The new dating now raises questions about the effects of the inferno on the world at that time. Further insights could thus lead to a better understanding of the evolution of the Earth in the post-dinosaur era, the scientists say.
Again and again there was an infernal crack: Many asteroids have hit our planet in the course of earth’s history and caused local or more far-reaching consequences. The most famous example is the massive impact that swept the dinosaurs off the evolutionary stage about 66 million years ago. The massive remains of the Chicxulub crater in the area of Mexico’s Yucatan Peninsula bear witness to this hit. In addition to this particularly large scar, other scars of considerable dimensions are also known. However, a particularly spectacular crater was only discovered in 2015: The structures of the Hiawatha crater were only revealed by an investigation using radar, because it lies dormant under a thick layer of ice in north-west Greenland.
How old is the crater under the ice?
According to the investigations, the Hiawatha crater has a diameter of about 31 kilometers – making it one of the 25 largest known impact craters on earth. It stands to reason that the impact once had far-reaching consequences for the earth’s climate. But when was that? So far, the comparatively little weathered structures suggested that the crater could still be young. This has led to some speculation: it seemed possible that the asteroid impacted Earth only 13,000 years ago. So perhaps it was responsible for the nearly 1,000-year-long global cooling known as the Younger Dryas, one speculates.
But as the new dating suggests, the Hiawatha impact may not have been a glacial climatic factor that might also have influenced the fate of our ancestors. The results of the international research team are based on analyzes of sand and rock that has been brought to light by water flowing out of the subsurface of the glacier in the area of the crater. “Since we discovered the crater seven years ago, we’ve worked hard to date it. We made several field trips to the area to collect samples related to the Hiawatha impact,” says co-author Nicolaj Larsen from the University of Copenhagen. Specifically, the samples now being examined are material that arose directly from the impact.
It crashed 58 million years ago
As the researchers explain, the shock-like overheating and melting led to changes in certain substances that allow a chronological classification by determining the decay processes. An argon-based study was carried out on the sand at the Natural History Museum of Denmark in Copenhagen – a 40Ar/39Ar dating. At the same time, the mineral zircon in the rock samples was subjected to uranium-lead dating at the Swedish Natural History Museum in Stockholm.
As the researchers report, the results of both approaches referred to the Paleocene – specifically to the time around 58 million years ago. This means that the Hiawatha crater is much older than previously thought. “The result of the age determination surprised us all,” says lead author Gavin Kenny from the Swedish Natural History Museum. His colleague Michael Storey from the Natural History Museum of Denmark says: “Since the two laboratories came to the same conclusion with different dating methods, I am convinced that we have determined the actual age of the crater”.
The new dating now also shows the circumstances under which the impact took place: When the asteroid Hiawatha hit the earth’s surface, the area in what is now northwestern Greenland was not yet covered by a kilometer-thick layer of ice. The temperatures were rather mild there, the region was forested and populated by animals, the researchers say. Our planet’s lifeworld was then just recovering from the catastrophic effects of the Chicxulub impact, which had occurred eight million years earlier.
Although far from being of this magnitude, the Hiawatha impact certainly devastated the region and potentially had far-reaching effects on the Earth’s climate and wildlife. So far, however, no clear traces of such an effect can be detected. But that could still come: The scientists say that further investigations could possibly show paleoecological and climatic consequences of the impact in the future.
Source: University of Copenhagen – Faculty of Science, professional article: Science Advances, doi: 10.1126/sciadv.abm2434