Has the earth´s sixth mass extinction already arrived? - Barnosky, Anthony D; Matzke, Nicholas; Tomiya, Susumu; Wogan, Guinevere O. U; Swartz, Brian; Quental, Tiago; Marshall, Charles; McGuire, Jenny L; Lindsey, Emily L; Maguire, Kaitlin C; Mersey, Ben; Ferrer, Elizabeth A (Nature, 2011)