[arcwhite]

Where are you getting this theory that there was an impact event that.killed off both the megafauna and the Clovis people's off?

Everything (credible) I'm able to find suggests/theorises that the Clovis differentiated into different groups of Native American populations, and that gradual climate change did most of the megafauna in.

[btilly]

There have been many interglacials and only in one did the megafauna die out en masse. This is a good argument against it simply being from climate change.

Instead look to what was different in the most recent one. A weird species on 2 feet with hunting techniques that the megafauna had never encountered before. Such as using fire to drive whole herds of horses off of a cliff.

[ncmncm]

Not plausible. Humans at much higher density had been able to drive island populations to extinction, but had not succeeded on a continent. Furthermore, they had been in the Americas for many millennia already.

Horses and camels were all over Asia, coeval with humans, and did fine. Lions survived in in Europe well into recorded history. Africa, of course, retained about everything for hundreds of millennia, except for 3 genera right at 12800 years ago. The only notable extinction in Eurasia was the woolly mammoth, which survived only on Wrangel Island. Humans had been in the Americas for many millennia, but populations of these animals did not decline during that time.

Instead, the 30+ genera and the Clovis people all vanished at identically the same time, coincident with the layer of radically elevated platinum dust, shocked quartz, and soot.

[ncmncm]

Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago.

Authors: Wendy S. Wolbach, Joanne P. Ballard, Paul A. Mayewski, [+24 others]

Journal of Geology, 2018, volume 126, pp. 165–184

http://sci-hub.se/10.1086/695703

Abstract: 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 km^2, or ∼9% of Earth’s terrestrial bio-mass. 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.