Once again, climate and extraterrestrial impacts have proven to be powerful drivers of the course of history and prehistory.
About 20,000 years ago was the peak of the ice age called the Last Glacial Maximum (LGM). That ice age was winding down when all of the sudden the "Younger Dryas", "a climatic period of extreme cooling that began around 12,800 ago and lasted about 1,400 years", began.
According to the lead author of a new study, Christopher Moore: "the Younger-Dryas coincides with the end of Clovis culture and the extinction of more than 35 species of ice-age animals. Moore says while evidence has shown that some of the animals were on the decline before Younger-Dryas, virtually none are found after it. Moore says that would indicate an extinction event for North America." The animals that went extinct included the mastodon, mammoth and saber-toothed tiger.
Now elevated platinum deposits at eleven Clovis archaeological sites and in the Greenland Ice sheet, all at the beginning of the Younger Dryas event suggest that "the most likely source of such platinum enrichment was from the impact of an extraterrestrial object," according to Moore, probably by a comet or asteroid about two-thirds of a mile in diameter. This would be much smaller than the CT boundary impact 65 million years ago that killed the dinosaurs, however, and no impact crater has been identified. According to the paper, these findings are corroborated previous study, Andronikov et al., that "investigated sediments from Belgium, the Netherlands, Lithuania, and NW Russia near Finland, reporting sharp YDB enrichment in Pt at the YD onset, as well as other meteoritic elements such as nickel, chromium, copper, and iridium."
The literature review explains that:
The Younger Dryas impact hypothesis proposed a causal link between a cosmic impact event and a) the onset of the YD climate cooling episode at ~12,800 calendar years BP, b) a peak in continental-scale biomass burning, c) extinction of more than 35 genera of North American Pleistocene megafauna, and d) the demise of the Paleoindian Clovis technocomplex. . . . Researchers have also hypothesized a human population decline or demographic shift immediately following the disappearance of the Clovis technocomplex at the YD onset.There was already substantial evidence linking this to an extraterrestrial impact at a quite narrow and well defined point in time according to literature review:
In support of those links, several studies have reported an exotic assemblage of impact-related proxies in a widely-distributed layer at the YDB, dating to 12,800 ± 150 Cal B.P. Impact proxies reported for YDB sites include but are not limited to high-temperature iron and silica-rich magnetic spherules, nanodiamonds, aciniform carbon (soot), high-temperature melt-glass, and elevated, above-background concentrations of nickel, osmium, and iridium. . . . Another investigation demonstrated the synchroneity of the YDB layer throughout its geographic range based on Bayesian modeling of data from 23 stratigraphic sections and 354 dates from 12 countries. The modeled YDB age range is 12,835–12,735 Cal B.P. (at 95% probability).
The abstract and the citation to the paper are as follows:
Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.Christopher R. Moore, et al., "Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences." 7 Scientific Reports 4403 (2017).