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http://www.nature.com/nature/journal/v471/n7336/full/nature09678.html Has the Earth’s sixth mass extinction already arrived? Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya, Guinevere O. U. Wogan, Brian Swartz, Tiago B. Quental, Charles Marshall, Jenny L. McGuire, Emily L. Lindsey, Kaitlin C. Maguire, Ben Mersey & Elizabeth A. Ferrer Affiliations Contributions Corresponding author Nature 471..