All scientific evidence suggests that several fragments of a comet hit earth about 13000 years ago causing massive floods and fires. This would have wiped out any cultures existing in North America, Europe and anyone living on coastlines and we know that humans have been in North America for over 130,000 years and at least one very important component for a large interconnected culture/civilization existed in North America 13,000 years ago, i.e. large mammals. In other words, a comet impact is the most important factor to consider when analyzing ancient human history as it would have destroyed most of the global population and wiped out many geographical regions completely.
Science Daily: Major cosmic impact 12,800 years ago Geologic and paleontological evidence unearthed in southern Chile supports the theory that a major cosmic impact event occurred approximately 12,800 years ago
Slate: Newly Discovered Alien Melt-Glass Supports Impact Theory on Mammoth Extinction
Science Alert: 13,000 Years Ago, a Comet Set Earth on Fire Says Shocking New Evidence
Roughly 12,800 years ago, planet Earth went through a brief cold snap that was unrelated to any ice age. For years, there have been geologists that have argued that this period was caused by an airburst or meteor fragments (known as the Younger Dryas Impact Theory).
BBC: Greenland ice sheet hides huge 'impact crater'
What looks to be a large impact crater has been identified beneath the Greenland ice sheet.
Scientific American: Did a Comet Hit Earth 12,000 Years Ago? Nanodiamonds found across North America suggest that major climate change could have been cosmically instigated
"Very strong impact indicators are found in the sediments directly above, and often shrouding in the case of Murray Springs, the remains of these animals and the people who were hunting them," says archaeologist and study co-author Doug Kennett of the University of Oregon in Eugene, the son in the father–son team helping to advance the new impact theory. "Is it a comet? Is it a carbonaceous chondrite? Was it fragmented? Was it focused? Based on the distribution of the diamonds, it was certainly large scale."
Preliminary searches further afield—Europe, Asia and South America—have turned up similar minerals and elements in sediments of the same age, Kennett says, and his own work on California's Channel Islands tells a tale of a massive burn-off, followed by erosion and a total change in the flora of the region.
"It's consistent with a fragmentary body breaking up with air shocks and possible surface impacts in various parts of North America. It could be above the ice sheet or offshore in the ocean," he says, explaining why no impact crater(s) has been found to date. "Immediate effects on the ground include high temperatures and pressures triggering major transformations of the vegetation, knocking trees over but also burning."
And that would make the climate shift of the Younger Dryas a closer cousin to the massive asteroid impact that wiped out the dinosaurs 65 million years ago. "This is an event that happened on one day," Kennett notes. "We're going to need high-resolution climate records, archaeological records, paleontological records to try to explore the effects."
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Note: Interestingly enough, this clip of PBS Eons shows some of the evidence of flooding that happened with the comet impact but leaves out the comet itself as this clip is outdated;
How 7,000 Years of Epic Floods Changed the World (w/ SciShow!)