For hundreds of thousands of years, mammoths thrived on Earth, roaming majestically through its frozen waters.
Then something happened. The Earth changed. And in a surprisingly short time, the mammothsMammutus primigenius) disappeared, with the last individuals going extinct 4,000 years ago on remote Wrangel Island in the cold Arctic.
In theory, humans contributed greatly It’s not clear what caused the climate change that put the mammoths at risk before their eventual decline. One theory is that a cosmic event struck Earth about 13,000 years ago, warming the planet beyond what the mammoths could tolerate, paving the way for other species to thrive.
this is Younger Dryas collision hypothesis (YDIH) Highly controversial right To say the leastBut some scientists believe there is a basis for this idea, and are looking for evidence to back it up.
One of them is University of South Carolina archaeologist Christopher Moore: “Some critics say, ‘Where’s the crater?'” Moore says“So far, not a single crater has been found.”
Still, Moore and his colleagues believe evidence will be found if they go beyond examining the Earth’s surface — and they think they’ve found some of it, in the form of minerals whose properties can best be explained by a cometary impact.
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Their latest paper cites several pieces of evidence: In totalTell a compelling story, they say.
The various pieces of evidence come from layers of sediment excavated from sites around the world, and have been radiocarbon dated to around 12,800 years ago, the time of the likely impact.
From approximately 50 locations around the world, including North and South America, Europe, Asia and the Greenland Ice SheetClues have been found that suggest Earth has encountered a comet.
Ice cores excavated from Greenland’s permafrost regions have revealed widespread fire-related particles, known as Combustion aerosols Particles were discovered that spread into the atmosphere when materials burn.
Samples from other parts of the world, including Syria, and three separate locations in North America have been found to contain unusually high amounts of platinum, which Moore said is rare in Earth’s crust but relatively common in comets.
The same sedimentary layer contains a dense concentration of very tiny iron balls. MicrospheresThey are formed by the ejection of molten material into the air, which occurs when a meteorite strikes the Earth’s surface or melts and explodes in the atmosphere.
And finally, the researchers are the first to report the presence of impact-fractured quartz grains in the Younger Dryas boundary layer across a large enough area of North America that they show microscopic fractures, a type of quartz that exhibits significant impact fractures.
“It’s like putting 75 elephants on a quarter.” Moore says“What we are seeing is the product of tremendous pressure.”
The bigger picture that emerges from these puzzle pieces is that a comet that struck Earth about 12,800 years ago may not have left a crater. If the comet had exploded in the atmosphere, its shock waves could have blanketed the surface and produced all of the elements observed, similar to how the Tunguska event caused mayhem without leaving a deep scar on the Earth’s surface.
But the evidence is far from conclusive. A paper published last December said: A team led by anthropologist Vance Holliday of the University of Arizona“The evidence and arguments purported to support YDIH contain flawed methodology, inappropriate assumptions, questionable conclusions, misstatements of fact, misleading information, unsupported claims, unrepeatable observations, logical errors, and selective omission of contrary information.”
Thus, more data will probably be needed before the scientific community is convinced. Still, other scientists have noted that many scientific theories that were once rejected or dismissed have later become widely accepted, so while it is important to remain skeptical, it is also useful to remain open-minded.
What is undeniable is that asteroid and comet impacts are worth studying in the context of large-scale environmental change, if not to understand history, then to guide decisions for the future. These events have changed the course of all life on Earth in the past, and although the Solar System is much calmer now, there is a non-zero chance that they will happen again in the future.
The new paper Airburst and crater formation.