title: Comment on "Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon".
abstract: Flowers and Farley (Reports, 21 December 2012, p. 1616; published online 29 November 2012) propose that the Grand Canyon is 70 million years old. Starkly contrasting models for the age of the Grand Canyon-70 versus 6 million years-can be reconciled by a shallow paleocanyon that was carved in the eastern Grand Canyon 25 to 15 million years ago (Ma), negating the proposed 70 Ma and 55 Ma paleocanyons. Cooling models and geologic data are most consistent with a 5 to 6 Ma age for western Grand Canyon and Marble Canyon.
authors.affiliation: University of New Mexico, Albuquerque, NM 87131, USA. kek1@unm.edu
authors.forename: Karl E
authors.initials: KE
authors.lastname: Karlstrom
authors.forename: John
authors.initials: J
authors.lastname: Lee
authors.forename: Shari
authors.initials: S
authors.lastname: Kelley
authors.forename: Ryan
authors.initials: R
authors.lastname: Crow
authors.forename: Richard A
authors.initials: RA
authors.lastname: Young
authors.forename: Ivo
authors.initials: I
authors.lastname: Lucchitta
authors.forename: L Sue
authors.initials: LS
authors.lastname: Beard
authors.forename: Rebecca
authors.initials: R
authors.lastname: Dorsey
authors.forename: Jason W
authors.initials: JW
authors.lastname: Ricketts
authors.forename: William R
authors.initials: WR
authors.lastname: Dickinson
authors.forename: Laura
authors.initials: L
authors.lastname: Crossey