There are five letters in this week’s PNAS, responding to an article by Isabel Israde-Alcántara et al., that came out earlier this year on purported impact markers in Lake Cuitzeo, Mexico. In one letter (Gill et al. 2012), my coauthors (Jessica Blois, Simon Goring, Jenn Marlon, Pat Bartlein, Andrew Scott, and Cathy Whitlock) and I raise concerns with the paleoecological interpretations of the lake record, calling on the the YD Impact team to “provide a clear explanation of the mechanism for observed ecological changes (or lack thereof) at the YD using conventional methods and rigorous statistical tests that report uncertainties for synchroneity.”
In a second paper, led by Maarten Blaauw along with Kathleen Nicoll and Vance Holliday (Blaauw et al. 2012), we explore problems with the construction of the chronology for the site, concluding that the purported impact layer “is not demonstrably or securely dated to the start of the YD, and indeed according to the evidence presented is most likely several millennia older.”
There are also accompanying letters by Mark Boslough on the Inconsistent impact hypotheses for the Younger Dryas, a letter from Tyrone Daulton on Suspect cubic diamond “impact” proxy and a suspect lonsdaleite identification, and a letter by Mark Hardiman, Andrew Scott, Margaret Collinson, and Scott Anderson on Inconsistent redefining of the carbon spherule “impact” proxy. You can also read Israde-Alcántara et al.’s response here, and a follow-up blog post by my co-author, Simon Goring.