There have been five past great mass extinctions during the history of Earth. There is an ever-growing consensus within the scientific community that we have entered a sixth mass extinction. Human activities are associated directly or indirectly with nearly every aspect of this extinction. This article presents an overview of the five past great mass extinctions; an overview of the current Anthropocene mass extinction; past and present human activities associated with the current Anthropocene mass extinction; current and future rates of species extinction; and broad science-curriculum topics associated with the current Anthropocene mass extinction that can be used by science educators. These broad topics are organized around the major global, anthropogenic direct drivers of habitat modification, fragmentation, and destruction; overexploitation of species; the spread of invasive species and genes; pollution; and climate change.
An Overview of Earth's Five Past Great Mass Extinctions
There have been five past great mass extinctions during the history of Earth (Jablonski, 1995; Erwin, 2001; see Figure 1). All five were characterized by “a profound loss of biodiversity during a relatively short period” (Wake & Vredenburg, 2008: p. 11466). The first mass extinction, the Ordovician—Silurian, occurred approximately () 439 million years ago (mya). The fifth, the Cretaceous—Tertiary, occurred 65 mya (Jablonski, 1995; Erwin, 2001). It was this extinction that saw the demise of the nonavian dinosaurs (Wake & Vredenburg, 2008). The most devastating mass extinction was the Permian—Triassic extinction (251 mya), in which 95% of all global species went extinct (Jablonski, 1995; Erwin, 2001).
An Overview of the Current Anthropocene Mass Extinction
There is an ever-growing consensus within the scientific community that we have entered a sixth mass extinction (McDaniel & Borton, 2002; Thomas et al., 2004; Lewis, 2006; Steffen et al., 2007; Alroy, 2008; Jackson, 2008; Rohr et al., 2008; Wake & Vredenburg, 2008; Rockströöm et al., 2009; Zalasiewicz et al., 2010). As Jeremy Jackson, director of the Center for Marine Biodiversity and Conservation and both the William E. and Mary B. Ritter Professor of Oceanography at the Scripps Institution of Oceanography and a senior scientist at the Smithsonian Tropical Research Institute, has written:
The great mass extinctions of the fossil record were a major creative force that provided entirely new kinds of opportunities for the subsequent explosive evolution and diversification of surviving clades. Today, the synergistic effects of human impacts are laying the groundwork for a comparably great Anthropocene mass extinction…with unknown ecological and evolutionary consequences. (Jackson, 2008: p. 11458)
In 2000, Paul Crutzen and Eugene Stoermer proposed that a new geological epoch had begun. They named the epoch the Anthropocene (pronounced an-thruh-po-seen) based on the “impact of human activities on earth and atmosphere” (Crutzen & Stoermer, 2000: p. 17). They stated that this geological epoch had begun in the “latter part of the 18th century” because by then “the global effects of human activities have become clearly noticeable” (Crutzen & Stoermer, 2000: p. 17). After this article and others (e.g., Crutzen, 2002; Crutzen & Steffen, 2003), the term “Anthropocene” entered the scientific literature informally (e.g., Steffen et al., 2004; Andersson et al., 2005; Crossland et al., 2005; Syvitski et al., 2005).
The Stratigraphy Commission of the Geological Society of London, by a large majority, decided in 2008 “that there was merit in considering the possible formalization of this term: that is, that it might eventually join the Cambrian, Jurassic, Pleistocene, and other such units on the Geological Time Scale” (Zalasiewicz et al., 2010: p. 2228). These 21 scientists from across the scientific community stated that “sufficient evidence has emerged” (Zalasiewicz et al., 2008: p. 7) for a new geological epoch named the Anthropocene (Crutzen & Stoermer, 2000; Crutzen, 2002) in reference to “the contemporary global environment dominated by human activity” (Zalasiewicz et al., 2008: p. 4). These human activities, which form the basis for the proposed ongoing Anthropocene epoch, are also the very activities that are driving the current mass extinction. Ultimately, the current Anthropocene epoch and the current mass extinction are interconnected and indivisibly united by the environmentally degrading human activities of the past 200 to 300 years.
Past & Present Human Activities Associated with the Current Anthropocene Mass Extinction
As Wake and Vredenburg (2008) wrote, “Human activities are associated directly or indirectly with nearly every aspect of the current extinction spasm” (p. 11472). These activities have taken many forms (see Figure 2). The most devastating and far-reaching anthropogenic direct drivers that are affecting global biodiversity are habitat modification, fragmentation, and destruction; overexploitation of species; the spread of invasive species and genes; pollution; and climate change (Millennium Ecosystem Assessment [MEA], 2005; World Wide Fund for Nature [WWF], 2008). Humans use between a third and half of all land on Earth and move more soil, rock, and sediment than all natural processes combined (Lewis, 2006). Humans have constructed reservoirs that hold three to six times as much water as are contained in natural rivers (Lewis, 2006) and use more than half of all accessible fresh water (Crutzen, 2002).
Through burning of fossil fuels, humans have elevated atmospheric CO2 concentrations to their highest levels in 15 million years, driving global warming, rising sea levels, and climate change (Tripati et al., 2009). Global fossil fuel emissions increased 29% from 2000 to 2008 and 41% from 1990 to 2008. The 29% increase from 2000 to 2008 occurred “in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source” (Le Quéré et al., 2009: p. 1).
At present, there are 6.8 billion humans on Earth. This number has increased tenfold in the past 300 years, fourfold in the past 100 years, and rough estimates place the global human population at 9 billion by 2040. Globally, 150 humans are born every minute. The global human “ecological footprint” exceeded Earth's biocapacity in the mid-to-late 1980s (WWF, 2008). Humans have become, through their sheer numbers and consumption rates, the greatest geophysical (Lewis, 2006) and evolutionary force on Earth (Palumbi, 2001).
Current & Future Rates of Species Extinction
The impact of human activities has greatly affected global biodiversity. There are between 5 million and 30 million extant species on Earth (Dirzo & Raven, 2003; MEA, 2005). Over the past 200 to 300 years, humans have accelerated global species extinction rates 100—1,000 times Earth's historical geological background rate (Pimm et al., 1995; Mace, et al., 2005; Rockström et al., 2009), and modeled future extinction rates are projected to be 10,000 times the background rate (MEA, 2005).
Currently, 32% of amphibians, 23% of mammals, 12% of birds, 25% of conifers, and 52% of cycads (a group of evergreen palm-like plants) are threatened with extinction (MEA, 2005). These approximate percentages are known only because these five groups are the only major taxonomic groups that have been comprehensively assessed as of 2004 (MEA, 2005). Twenty percent “of known coral reefs have been destroyed and another 20% degraded in the last several decades” (MEA, 2005). As of 2008, there were an estimated 1,642,189 described species worldwide, only 44,838 of which had been assessed in terms of conservation status by the International Union for Conservation of Nature (IUCN) Red List. Of the 44,838 species on the 2008 IUCN Red List, over one-third (i.e., 16,928 species) were threatened with extinction (IUCN, 2009).
Further evidence comes from the Living Planet Index (WWF, 2008). The Living Planet Index is a measurement of global biodiversity. It is based on the trends of nearly 5,000 populations of 1,686 species of mammals, birds, reptiles, amphibians, and fish throughout Earth. Using this index, a 30% decline in biodiversity has been observed from 1970 to 2005 (WWF, 2008).
Approximately two-thirds of all organisms occur in the tropics, mainly in tropical humid forests (Pimm & Raven, 2000). More than half of the tropical humid forests on Earth have been destroyed. At current deforestation rates, it is estimated that the remaining tropical humid forests and the species they contain will be destroyed by 2060. If this were to occur, the extinction rate in these forests by 2060 would be ≈48,000 extinctions per million species per decade (Pimm & Raven, 2000). McDaniel and Borton (2002) stated that human industrial societies have monopolized Earth's biological energy flow and that when the current global modern societies' use of the planet's biological energy is compared with past hunter-gatherer societies, “the current mass extinction appears as a predictable, expected result” (p. 929).
Education: A Mechanism of Reducing Global Environmental Degradation?
One component of possibly reducing the rising anthropogenic affects associated with the current Anthropocene mass extinction is education. The current Anthropocene mass extinction constitutes a newly emerging scientific theme that has great potential in science education. Because the current Anthropocene mass extinction has components related to life science and physical science, it offers many opportunities for integration across multiple disciplines (e.g., biology, chemistry, geology, and meteorology), multiple science courses, and other nonscience courses (e.g., social studies and mathematics) (National Research Council [NRC], 1996: p. 214 [see third paragraph and Program Standard C]). The theme also allows for implementation of scientific inquiry activities (NRC, 1996: p. 214 [see second paragraph]) in both formal educational settings (e.g., indoor and outdoor classrooms) and informal educational settings (e.g., nature centers and zoos) (NRC, 2009). Lastly, the theme is relevant to all students because in the future, on some level, it will affect their own quality of life and the well-being of other organisms (NRC, 1996: p. 212 [see Program Standard B]).
Broad Science-Curriculum Topics Associated with the Current Anthropocene Mass Extinction
Because of these unique characteristics, the current Anthropocene mass extinction offers an abundance of educational opportunities for science educators. The major global anthropogenic direct drivers of biodiversity loss associated with the current Anthropocene mass extinction provide an excellent organizational framework for presenting the complexity and human challenges of this mass extinction. Figure 3 presents these direct drivers. Under each direct driver, broad science-curriculum topics are presented that can be used by science educators. Topics can be combined to integrate across drivers and across both physical and life-science disciplines. For all of the drivers, the scale of human impact can be addressed at the ecosystem, biome, or biosphere level. When a topic is used, it should be combined with topics and examples that address humanity's ability to ethically reduce the current trajectory of local, regional, and global environmental degradation. These topics include but are not limited to reduction of human consumption rates (i.e., per capita natural resources and ecological services) in developed countries; reduction in global human population growth; and development and implementation of environmentally sustainable human activities.
Clearly, the greatest challenge facing humanity is stopping the destruction of the very biosphere that sustains us. The current Anthropocene mass extinction provides an emerging, integrative, inquiry-based, and relevant theme for educating students about global environmental degradation and how it might be reduced. Ultimately, educating students about the current Anthropocene mass extinction is key to giving them the knowledge and skills necessary to be scientifically literate citizens (Rutherford & Ahlgren, 1990; American Association for the Advancement of Science, 1993) who can fully participate in this, humanity's greatest challenge.
References & Further Reading
Note: An asterisk indicates that the document is free online and can be incorporated into middle school, high school, and college science courses.