Five past great mass extinctions have occurred during Earth's history. Humanity is currently in the midst of a sixth, human-induced great mass extinction of plant and animal life (e.g., Alroy 2008; Jackson 2008; Lewis 2006; McDaniel and Borton 2002; Rockstrom et al. 2009; Rohr et al. 2008; Steffen, Crutzen, and McNeill 2007; Thomas et al. 2004; Wake and Vredenburg 2008; Zalasiewicz et al. 2010). This article explains the first five great mass extinctions, the current great mass extinction, and the human activities and rates of species extinction associated with the current extinction. The sixth great mass extinction can be used to teach students about environmental change and its impacts and extinction. (Contains 3 figures, 9 online resources and 3 resources.)