A major event caused a massive drop in the average temperature of the Earth 12,800 years ago, causing some regions in the Northern Hemisphere to cool down by 14 degrees Fahrenheit.
Modern geology points out that the failure of glacial ice dams in holding back large lakes in Central North America caused this climate change event, named the Younger Dryas. It triggered the release of massive amounts of fresh water into the North Atlantic. The sudden blast halted ocean circulation and caused the abrupt drop in the climate.
The impact hypothesis
However, several geologists believe differently and refer to what is called the impact hypothesis. It implies that a bolide impact or the impact of a fragmented comet or asteroid 12,800 years ago caused the abrupt climate change.
Archaeologist Caleb Vance Haynes Jr. identified a carbon-rich black layer, also known as black mats, and the age of the base of this layer coincides with the beginning of the Younger Dryas. The presence of these black mats also suggests the Younger Dryas caused the abrupt extinction of the megafauna and avian taxa. The remains, found at Murray Springs, Arizona, were found directly beneath the black layer. Haynes Jr. explained that the ice-age megafauna extinction came before the deposition of the black layer.
Researchers also looked into the Younger Dryas Boundary stratigraphic layer, a layer of sediments within the Earth caused by processes like massive floods or the displacement of sediment via wind or water.
In the last few years, materials found in the Boundary show a variety of rare impact-related materials, such as fragments of silica-rich magnetic spheres, nanodiamonds, soot, high-temperature melt-glass, carbon spherules, fullerenes enriched with helium-3, and elevated concentrations of nickel, osmium, iridium, and platinum. According to researchers, volcanic, anthropogenic, and natural processes cannot explain the presence of these materials in the Boundary.
The impact of winter
The impact is believed to have caused not only disruptions in the glacial ice sheet and halting ocean circulation but also may have caused an impact winter by setting off massive wildfires that covered the atmosphere with its smoke, making sunlight unable to pass through the dense particles.
Pieces of evidence shown by scientists studying the ocean, lake, terrestrial, and ice core records support the existence of the fires. These records show significant amounts of particles correlated with burning, like charcoal and soot, that were present around the time the Younger Dryas was beginning.
This climate change event was the starting point of the dying-out of ice-age giants, such as the mammoths and mastodons, eventually leading to the extinction of more than 35 genera of animals across North America.
To give an analogy, if a sudden drop in temperature like that happened today, the air around tropical getaways like Hawaii and Bora-Bora would suddenly get as cold as Montreal, Canada. In Greenland, the layers of ice denote that the sudden drop in temperature in the Northern Hemisphere lasted about 14,000 years.
Though many studies have been providing evidence that the impact did happen, others have failed to replicate evidence. Other scientists dispute that materials such as the microspherules and nanodiamonds can be formed through other phenomena and do not solely rely on the impact of an asteroid or comet.
