Cosmic Shrapnel That Killed The Mammoth Is Buried Deep, Scientists Claim

For vast stretches of prehistory, the woolly mammoth roamed the planet’s icy expanses, its heavy gait pressing steadily across frozen landscapes.

That long dominance ended abruptly. Conditions shifted, and within what seems like a brief interval the mammoths (Mammuthus primigenius) disappeared. The final survivors are thought to have died out around 4,000 years ago on isolated Wrangel Island, far up in the Arctic north.

Researchers often argue that people played a major role in the species’ decline, yet the drivers behind the climatic disruption that placed mammoths under such strain remain uncertain. One proposed explanation is that Earth experienced a cosmic incident close to 13,000 years ago, pushing temperatures beyond what mammoths could withstand and opening ecological space for other species to flourish.

The Younger Dryas impact hypothesis (YDIH) and why it is disputed

This proposal is known as the Younger Dryas impact hypothesis (YDIH). Describing it as controversial would be an understatement. Even so, some scientists maintain that it is plausible and have continued searching for evidence that might support it.

Among them is archaeologist Christopher Moore of the University of South Carolina. “Some of our critics have said, ‘Where’s the crater?’” Moore says. “As of now, we don’t have a crater or craters.”

Moore and colleagues argue that the relevant signals may not be apparent from a simple surface inspection. They contend that clues are present deeper in Earth’s record, including minerals whose characteristics, in their view, are most readily accounted for by a comet impact.

In their latest paper, the team sets out several of these independent strands of evidence which, taken together, they say form a persuasive narrative.

Sediments dated to ~12,800 years ago: where the evidence comes from

The reported indicators come from sediment layers excavated at locations around the world. Using radiocarbon analysis, these layers have been dated to roughly 12,800 years ago-the time window in which the hypothesised impact is proposed to have occurred.

From about 50 sites globally-spanning North and South America, Europe, Asia, and the Greenland ice sheet-researchers describe findings they interpret as potentially consistent with Earth encountering a comet.

Signs in Greenland ice and elsewhere

Ice cores extracted from Greenland’s permanently frozen regions contain microparticles linked with extensive fires-so-called combustion aerosols, which can spread widely through the atmosphere when material burns.

Elsewhere, including Syria and three far-apart sites in North America, investigators report unusually high amounts of platinum. Platinum, Moore notes, is scarce in Earth’s crust but comparatively common in comets.

Within the same sedimentary layer, the researchers also describe raised levels of minuscule iron spheres known as microspherules. These can form when molten matter is sprayed through the air, as can happen when a meteorite strikes the ground or melts and explodes in the atmosphere.

Finally, the team reports- for the first time-grains of shock-fractured quartz in the Younger Dryas boundary layer across multiple widely separated locations in North America. This refers to quartz showing microscopic cracking produced by a substantial shock.

“It’s like putting 75 elephants on a quarter,” Moore says. “It’s a tremendous amount of pressure that creates what we’re seeing.”

A comet airburst without a crater?

From these pieces, the broader scenario they propose is a comet hitting Earth around 12,800 years ago in an event that may not have produced a crater. If the object detonated in the atmosphere, they suggest, the resulting shockwave could have swept across the surface and generated the collection of signals they describe-similar, in principle, to how the Tunguska event caused enormous disturbance without leaving a deep scar in the planet’s surface.

Even so, the case is a long way from definitive. In a paper published in December last year, a group led by anthropologist Vance Holliday of the University of Arizona stated: “Evidence and arguments purported to support the YDIH involve flawed methodologies, inappropriate assumptions, questionable conclusions, misstatements of fact, misleading information, unsupported claims, irreproducible observations, logical fallacies, and selected omission of contrary information.”

Why more evidence will be needed

As a result, substantially more data will likely be required before the wider scientific community is close to accepting the hypothesis. At the same time, some researchers note that ideas once dismissed have, in other cases, later gained broad acceptance-so while scepticism is essential, it may also be worthwhile to stay open-minded.

What is not in dispute is that asteroid and comet impacts are worth examining when considering large-scale environmental change-not only to better understand the past, but also to inform choices for the future. Such events have redirected the trajectory of life on Earth before, and although the Solar System is calmer than it once was, the chance of another occurring in the future is not zero.

The new paper has been published in Airbursts and Cratering Impacts.