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A study by the University of Chicago says a cosmic impact (illustrated) is the best explanation for the 'Big Freeze' 12,800 years ago. They say evidence for this comes from nanodiamonds scattered across 11 countries that could only have come from space


* A study by the University of Chicago says a cosmic impact is the best explanation for the 'Big Freeze' 12,800 years ago

* They say evidence for this comes from nanodiamonds scattered across 11 countries that could only have come from space

* The material is found in a thin layer just a few metres below the surface

* And they also formed at temperatures in excess of 2,200°C (4,000°F)

* This suggests they were likely created by a major impact event

* Several other theories have been suggested for this Younger Dryas period nearly 13,000 years ago, including wildfires and a solar flare

* But this latest evidence suggests a cosmic impact is the best theory


Around 12,800 years ago Earth was plunged into a 'Big Freeze', resulting in the extinction of many species. What caused this event, however, is not known.

One theory is that Earth was struck by a comet or asteroid at the time and now new research supporting the theory has been released.

By studying nanodiamonds scattered across Europe, North America and South America, the researchers say the impact theory is right.

In the University of Chicago study, scientists claim the Younger Dryas (YD) period - the name given to the cooling episode about 12,800 years ago - was the result of a cosmic impact.

This drastic climate change coincided with the extinction of Pleistocene megafauna, such as the saber-tooth cats and the mastodon, and resulted in major declines in prehistoric human populations, including the end of the prehistoric Paleo-Indian Clovis culture.

The result of the impact, they say, was a YD Boundary (YDB) layer of nanodiamonds scattered over 19 million square miles (50 million square km).

Nanodiamonds are types of diamond that result from detonations or explosions.

'In [11] countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds, a major cosmic-impact proxy,' Professor James Kennett and his colleagues wrote.

Microscopic nanodiamonds, melt-glass, carbon spherules, and other high-temperature materials are found in abundance throughout the YDB field, in a thin layer located only metres from the Earth's surface.

Because these materials formed at temperatures in excess of 2,200°C (4,000°F), the fact they are present together so near to the surface suggests they were likely created by a major extraterrestrial impact event, such as an asteroid.

In addition to providing support for the cosmic impact hypothesis, the study also offers evidence to reject alternate hypotheses for the formation of the YDB nanodiamonds, such as wildfires and increased volcanic activity.

With limited evidence, several rival theories have been proposed about the event that sparked this period, such as a collapse of the North American ice sheets, a major volcanic eruption, or a solar flare.

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According to the study the result of the impact was a YD Boundary (YDB) layer scattered over 19 million square miles (50 million square kilometres). Through the regions shown in this map material is found in a thin layer just a few metres below the surface across the globe
Based on multiple analytical procedures, the researchers determined that the majority of the materials in the YDB samples are nanodiamonds and not some other kinds of minerals.

The analysis showed that the nanodiamonds consistently occur in the YDB layer over broad areas.

To date, scientists know of only two layers on Earth in which nanodiamonds have been found in various locations, indicating an impact event.

These are the YDB layer in this study and the well-known Cretaceous-Tertiary boundary 65 million years ago, which is marked by the mass extinction of the dinosaurs.

'The evidence we present settles the debate about the existence of abundant YDB nanodiamonds,' Kennett said.

The study, 'Nanodiamond-rich layer across three continents consistent with major cosmic impact,' was published in the Journal of Geology.

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Material from the YDB layer, carbon spherules shown here, formed at temperatures in excess of 2,200°C (4,000°F). This suggests they were likely created by a major impact event. Several other theories have been suggested for this Younger Dryas period nearly 13,000 years ago, including wildfires and a solar flare
WHAT WAS THE YOUNGER DRYAS?

The Younger Dryas period is also known as the Big Freeze.

It was a period of cold climatic conditions and drought that took place between 12,800 and 11,500 years ago.

Scientists believe this change in climate was caused by a meteor impact, but another theory is that it was because of the collapse of the North American ice sheets.

During the period, forests in Scandinavia were replaced with a glacial tundra.

There was more dust in the atmosphere that originated from deserts in Asia.

The drier conditions caused drought in the Levant, known as the region of Syria or the Eastern Mediterranean, which led inhabitants to agriculture.

The change in climate is especially linked to the development of cereal cultivation.