title: Geochronology: age of Mexican ash with alleged 'footprints'.
abstract: A report of human footprints preserved in 40,000-year-old volcanic ash near Puebla, Mexico (http://www.royalsoc.ac.uk/exhibit.asp?id=3616&tip=1), was the subject of a press conference that stirred international media attention. If the claims (http://www.mexicanfootprints.co.uk) of Gonzalez et al. are valid, prevailing theories about the timing of human migration into the Americas would need significant revision. Here we show by 40Ar/39Ar dating and corroborating palaeomagnetic data that the basaltic tuff on which the purported footprints are found is 1.30+/-0.03 million years old. We conclude that either hominid migration into the Americas occurred very much earlier than previously believed, or that the features in question were not made by humans on recently erupted ash.
authors.affiliation: Berkeley Geochronology Center, Berkeley, California 94709, USA. prenne@bgc.org
authors.forename: Paul R
authors.initials: PR
authors.lastname: Renne
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Feinberg
authors.forename: Michael R
authors.initials: MR
authors.lastname: Waters
authors.forename: Joaquin
authors.initials: J
authors.lastname: Arroyo-Cabrales
authors.forename: Patricia
authors.initials: P
authors.lastname: Ochoa-Castillo
authors.forename: Mario
authors.initials: M
authors.lastname: Perez-Campa
authors.forename: Kim B
authors.initials: KB
authors.lastname: Knight
mesh_terms: D005075:Biological Evolution; D004641:Emigration and Immigration / Q000266:history*; D005580:Fossils; D049690:History, Ancient; D006801:Humans; D020407:Internet; D008280:Magnetics; D008800:Mexico; D015203:Reproducibility of Results; D018707:Volcanic Eruptions