Those three things are the extinction of the megafauna, the disappearance of the Clovis culture and the climate change of the Younger Dryas. The general thought has been that climate change played a key role in wiping out the large animals and perhaps undermining the Clovis people, though some scientists have argued that the animals were hunted to extinction (the Pleistocene overkill hypothesis). But the fossil record has been puzzling, for many species of megafauna had survived multiple ice ages until the cool spell of the Younger Dryas.
For decades, scientists have believed that meltwater at the end of the ice ages formed a huge lake in central North America, known to scientists as Lake Agassiz. At some point, the water from that lake may have surged into the North Atlantic and shut down the dominant ocean current that brought warmer water toward higher latitudes. That, in turn, could have created a long-term climate change.
The impact scenario incorporates the meltwater scenario. The scientists say that the impact could have destabilized and melted the edges of the ice sheet resting on the northern tier of the continent. An impact would also have created a short-term environmental disaster. Dust from the impact and soot from continent-spanning wildfires could have risen into the atmosphere, blocked sunlight and dramatically hampered plant growth. With vast portions of the landscape burned, large animals requiring a great deal of food may have died off, even if they had survived the initial catastrophe.
On the one hand, maybe that was our once every 50 million years hit and we’re all safe, or on the other maybe the smaller-but-still-destructive stuff is much more common than we would like to think.
It probably wouldn’t take even a continental catastrophe to wipe out a neolithic culture or a bunch of megafauna. All you need are a couple bad seasons for the whole house of cards to come down, especially because competitors from less-affected areas will be moving in immediately.
Kinda makes you think about how little it would take to disrupt the current house of cards.