Supporters of the impact theory have put forth 29 sites, from North America to Europe and beyond, that contain a thin layer of sediments said to date to the start of the cosmic impact event. The latest study checked to see whether those sites were all really 12,800 years old.
Only 3 of the 29 are, the researchers report today in the Proceedings of the National Academy of Sciences1. The other sites either have not been dated using the usual radiometric methods, or are much older or younger than the reported impact. “The chronology doesn’t hold up,” says team leader David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas.but:
Impact supporters are not about to give up. “Meltzer’s analysis of the dates is overly simplistic and clearly biased towards his conclusions,” says Richard Firestone, a nuclear chemist at Lawrence Berkeley National Laboratory in California and leader of the impact theory. Errors in radiocarbon dating mean that not all of the sites will date precisely to 12,800 years ago, Firestone argues. And much of his team's argument relies on cross-correlating various sites containing impact markers, some with good radiocarbon dates and some without.PNAS doi: 10.1073/pnas.1401150111
Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago
David J. Meltzer et al.
A key element underpinning the controversial hypothesis of a widely destructive extraterrestrial impact at the onset of the Younger Dryas is the claim that 29 sites across four continents yield impact indicators all dated to 12,800 ± 150 years ago. This claim can be rejected: only three of those sites are dated to this window of time. At the remainder, the supposed impact markers are undated or significantly older or younger than 12,800 years ago. Either there were many more impacts than supposed, including one as recently as 5 centuries ago, or, far more likely, these are not extraterrestrial impact markers.