For hundreds of thousands of years, the woolly mammoth thrived on Earth, measuring its majestic run across frozen lands.
Then something happened. The earth has changed. And in a remarkably short time mammoths (Mammuthus primigenius) were gone, the last of them dying out 4,000 years ago on remote Wrangel Island in the cold arctic north.
Although humans are theorized to have contributed significantly to their eventual decline, it is unclear what factors may be driving climate change to put them at risk. One idea is that a cosmic event hit Earth nearly 13,000 years ago that warmed the world beyond what was tolerable for mammoths, paving the way for other species to thrive.
It’s called the Younger Dryas Impact Hypothesis (YDIH), and to call it highly controversial might be putting it mildly. Still, some scientists believe the idea has legs and have been looking for evidence to support it.
One of them is archaeologist Christopher Moore from the University of South Carolina. “Some of our critics said, ‘Where’s the crater?'” Moore says. “As of now, we have no crater or craters.
However, Moore and his colleagues believe that evidence can be found if you do more than a surface survey. And they also believe they’ve found some of it—in the form of minerals with properties they say are best explained by a comet impact.
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In their latest paper, they describe several of these lines of evidence In totalthey say, they tell an engaging story.
The various pieces of evidence come from layers of sediment excavated from sites around the world, all dated by radiocarbon dating to about 12,800 years ago – the period in which the impact is thought to have occurred.
From around 50 locations worldwide, including the Americas, Europe, Asia and the Greenland Ice Sheetclues have appeared that could indicate an encounter between Earth and a comet.
In ice cores excavated from permafrost regions of Greenland, microparticles associated with large-scale fires have been discovered – so-called combustion aerosols, which spread through the atmosphere when matter burns.
Unusually high amounts of platinum can be found in samples taken from other parts of the world, such as Syria, and three widely separated locations in North America. Platinum, Moore explains, is rare in Earth’s crust but relatively common in comets.
In the same sedimentary layer there is an increased concentration of tiny microscopic balls of iron called microspherules. These form when molten material sprays through the air, which occurs when a meteorite either hits the surface or melts and explodes in the atmosphere.
Finally, researchers report for the first time the presence of impact-broken quartz grains in the Younger Dryas boundary layer at a number of well-separated locations in North America. It is a quartz that exhibits microscopic fractures due to significant shock.
“It’s like putting 75 elephants in a quarter,” says Moore. “It’s a huge amount of pressure that creates what we see.”
The bigger picture that might emerge from these puzzle pieces is a comet that hit Earth about 12,800 years ago in an impact that may not have left a crater. If a comet exploded in the atmosphere, the resulting shock wave could flood the surface and create all the observed features, much like the Tunguska event created a giant noise without leaving a deep scar on the planet’s surface.
However, it is very far from a smoking gun. In a paper published last December, a team led by University of Arizona anthropologist Vance Holliday noted: “The evidence and arguments purporting to support the YDIH include flawed methodologies, inappropriate assumptions, questionable conclusions, incorrect facts, misleading information, unsubstantiated claims, non-reproducible observations, logical fallacies and selective omission of contrary information.”
So we’ll probably need a lot more data before the scientific establishment is even close to being convinced. Still, other scientists point out that in the past, many scientific theories that were once dismissed or dismissed later gained widespread consensus, so while it’s important to remain skeptical, it can pay to keep an open mind.
There’s no denying that asteroid and comet impacts are certainly worth investigating in relation to large-scale environmental change, if not to understand history than to help guide our decisions for tomorrow. These events previously changed the course of all life on Earth, and although the Solar System is much more peaceful than it once was, the possibility of another happening in the future is not zero.
A new article was published in Air bursts and craters.