AP LONDON - British scientists claimed on Tuesday to have unearthed 40,000-year-old human footprints in central Mexico, challenging previous studies that put the arrival of the first humans in the Americas at about 13,500 years ago. Scientists Silvia Gonzalez, from Liverpool John Moores University, and Matthew Bennett, of Bournemouth University, found the footprints in an abandoned quarry close to the Cerro Toluquilla volcano in the Valsequillo Basin...Continued at MSNBC