Stratigraphic and earth system approaches to defining the anthropocene Will Steffen, Reinhold Leinfelder, Jan Zalasiewicz, Colin N. Waters, Mark Williams, Colin Summerhayes, Anthony D. Barnosky, Alejandro Cearreta, Paul Crutzen, Matt Edgeworth, Erle C. Ellis, Ian J. Fairchild, Agnieszka Galuszka, Jacques Grinevald, Alan Haywood, Juliana Ivardo Sul, Catherine Jeandel, J.R. McNeill, Eric Odada, Naomi Oreskes, Andrew Revkin, Daniel de B. Richter, James Syvitski, Davor Vidas, Michael Wagreich, Scott L. Wing, Alexander P. Wolfe, and H.J. Schellnhuber