The Younger Dryas boundary (YDB) cosmic-impact hypothesis is based on considerable evidence that Earth collided with fragments of a disintegrating ≥100-km-diameter comet, the remnants of which persist within the inner solar system ∼12,800 y later. Evidence suggests that the YDB cosmic impact triggered an “impact winter” and the subsequent Younger Dryas (YD) climate episode, biomass burning, late Pleistocene megafaunal extinctions, and human cultural shifts and population declines. The cosmic impact deposited anomalously high concentrations of platinum over much of the Northern Hemisphere, as recorded at 26 YDB sites at the YD onset, including the Greenland Ice Sheet Project 2 ice core, in which platinum deposition spans ∼21 y (∼12,836–12,815 cal BP). The YD onset also exhibits increased dust concentrations, synchronous with the onset of a remarkably high peak in ammonium, a biomass-burning aerosol. In four ice-core sequences from Greenland, Antarctica, and Russia, similar anomalous peaks in other combustion aerosols occur, including nitrate, oxalate, acetate, and formate, reflecting one of the largest biomass-burning episodes in more than 120,000 y. In support of widespread wildfires, the perturbations in CO2 records from Taylor Glacier, Antarctica, suggest that biomass burning at the YD onset may have consumed ∼10 million km2, or ∼9% of Earth’s terrestrial biomass. The ice record is consistent with YDB impact theory that extensive impact-related biomass burning triggered the abrupt onset of an impact winter, which led, through climatic feedbacks, to the anomalous YD climate episode.
The most famous ice age of them all— the one directly preceding the rise of civilization— turned out to have been caused by a carpet bombing of meteors from a comet.
And you have to note, civilization arose because we needed to grow food since all the food around us was dying thanks to the plummeting temperatures. So if not for this comet, we might still be hunter-gatherers or in very primitive civilizations right now. That, or maybe we'd be much more advanced since it's possible civilization actually started much earlier than we know but this impact wiped them out.
Curiously, the firestorm it caused lasted for much longer than the KT impact that wiped out the dinosaurs, but here we are. Then again, the story might've been different if we were struck by the comet itself rather than its much smaller fragments. A 60-mile-wide comet would knock the Earth off its axial tilt ever so slightly and push us a bit off our orbit. Among other things.
In a hugely detailed and comprehensive new study, researchers have painted a picture of how around a tenth of Earth's surface suddenly became covered in roaring fires at a point some 12,800 years ago.
The firestorm rivals the one that wiped out the dinosaurs, and it was caused by fragments of a comet that would have measured around 100 kilometres (62 miles) across.
As dust clouds smothered the Earth, it kicked off a mini ice age that kept the planet cool for another thousand years, just as it was emerging from 100,000 years of being covered in glaciers. Once the fires burned out, life could start again, according to the international team of scientists.
"The hypothesis is that a large comet fragmented and the chunks impacted the Earth, causing this disaster," says one of the team, Adrian Melott from the University of Kansas.
"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 kilometres [3.86 million square miles], was consumed by fires."
To peer back into the burning fires and shock waves of this major event, a large number of geochemical and isotopic markers were measured from more than 170 sites across the world, involving a team of 24 scientists.