The Sixth Great Mass Extinction
Wagler, Ron, Science Scope
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. The topics and resources discussed here can also be aligned to all seven of the crosscutting concepts in A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (NRC 2011, 4-1-4-2), which include examples such as cause and effect: mechanism and explanation; scale, proportion, and quantity; systems and system models; and stability and change.
Earth's past great mass extinctions
The Earth is over 4.5 billion years old (Dalrymple 2001), and during the planet's history, five past great mass extinctions have occurred (Erwin 2001; Jablonski 1995). During all of these past great mass extinctions, there was an enormous loss of life in a short time (see Figure 1). The first great mass extinction occurred approximately 439 million years ago; the fifth took place approximately 65 million years ago (Erwin 2001; Jablonski 1995). The fifth great mass extinction is the most well known to the general public because it involved the extinction of the non-avian dinosaurs (Wake and Vredenburg 2008) and the survival of the only existing living group of dinosaurs, the birds. The most destructive past great mass extinction was the Permian-Triassic extinction, in which 95% of Earth's species went extinct (Erwin 2001; Jablonski 1995)
FIGURE 1 Earth's past great mass extinctions Name Number Date of Cause of extinction extinction Ordovician-Silurian 1st* ~439 Fluctuations in sea level; extinction million extensive glaciations; years ago global warming Late Devonian 2nd* ~364 Global cooling after extinction million bolide (large exploding years ago meteor) impacts may have been responsible. Permian-Triassic 3rd ~251 Causes are debated. The extinction million leading candidate is flood years ago volcanism. This led to profound climate change. The volcanism may have been initiated by a bolide impact. End Triassic 4th ~199-214 "Opening of the Atlantic extinction million Ocean by seafloor years ago spreading related to massive lava floods that caused significant global warming." Cretaceous-Tertiary 5th ~65 million Causes are debated. extinction years ago Possible causes include a giant asteroid impact in the Gulf of Mexico and climatic changes resulting from volcanic floods in India. Name Loss of life 1 Ordovician-Silurian "Approximately 25% of the extinction families and nearly 60% of the genera of marine organisms were lost. …