A new study suggests that, on a day about 12,800 years ago, Earth collided with fragments of a disintegrating comet, igniting fires across the globe. The large study, of geochemical and isotopic markers from 170 different sites around the world, was published in two papers in the Journal of Geology on February 1, 2018 (here and here).
At the time, the Earth had emerged from an ice age. Things were warming up, and the glaciers had retreated. In a statement, the researchers imagined what it might have been like for humans at the time:
Out of nowhere, the sky was lit with fireballs. This was followed by shock waves.
Fires rushed across the landscape, and dust clogged the sky, cutting off the sunlight. As the climate rapidly cooled, plants died, food sources were snuffed out, and the glaciers advanced again. Ocean currents shifted, setting the climate into a colder, almost “ice age” state that lasted an additional thousand years.
Finally, the researchers said, the climate began to warm again. This world had fewer large animals, evidenced by, for example, completely different kinds of spear points left behind by North American people of that time.
The researchers believe the data suggests the disaster was touched off when Earth collided with fragments of a disintegrating comet that was roughly 62 miles (100 km) in diameter — the remnants of which persist within our solar system to this day.
Adrian Melott, professor of Physics and Astronomy at University of Kansas is a study author. Melott said in a statement:
The hypothesis is that a large comet fragmented and the chunks impacted the Earth, causing this disaster. A number of different chemical signatures — carbon dioxide, nitrate, ammonia and others — all seem to indicate that an astonishing 10 percent of the Earth’s land surface, or about 10 million square kilometers [3.9 million square miles], was consumed by fires.
According to Melott, analysis of pollen suggests pine forests were probably burned off to be replaced by poplar, which is a species that colonizes cleared areas.
The authors suggest that the cosmic impact could even have touched off the Younger Dryas cool episode, a temporary return to glacial conditions, as well as biomass burning, late Pleistocene extinctions of larger species and human cultural shifts and population declines. Melott said:
Computations suggest that the impact would have depleted the ozone layer, causing increases in skin cancer and other negative health effects.The impact hypothesis is still a hypothesis, but this study provides a massive amount of evidence, which we argue can only be all explained by a major cosmic impact.
Bottom line: According to a new study of geochemical and isotopic markers, around 12,800 years ago, Earth collided with fragments of a disintegrating comet, igniting fires across the planet.