Academic journal article The Science Teacher

Going Extinct

Academic journal article The Science Teacher

Going Extinct

Article excerpt

Extinction is the fate of every species on Earth. Millions of species have appeared (speciation) and disappeared (extinction) since life began. In fact, 99% of all species that have ever existed are gone (Friedland and Relyea 2012). Extinction is natural: Environmental conditions change, a species fails to adapt, and its population dwindles to zero.

Background extinction: Every year, approximately one species among all living things, on average, becomes extinct (Friedland and Relyea 2012). Meanwhile, new species arise through evolution and speciation. For example, if two populations of the same species are isolated geographically and reproductively, they may become two new species. Because speciation is faster than background extinction, species grow in number over time. Scientists have identified almost 1.5 million current species but estimate the total may be about 8.7 million (Mora 2011) and possibly much higher.

Mass extinction: When a global environmental change occurs, the Earth can experience a mass extinction. The most recent--the Cretaceous-Tertiary extinction--happened about 65 million years ago, possibly due to a several-km-wide meteorite striking the Earth. This extinction claimed the dinosaurs and an estimated 16% of marine families, 47% of marine genera, and 18% of land vertebrate families (Davis and Nagle 2010). Five mass extinctions have occurred, and some scientists worry that a sixth is happening now. Evidence for this includes increasing extinction rates and decreasing biodiversity (Davis and Nagle 2010).

Classroom activities

Species extinction relates to units on evolution, natural selection, speciation, extinction, biodiversity, and/or human impacts on ecosystems.

In a New York Times Learning Network activity, students learn about mass extinctions, map extinction events to a geologic timeline, and explore whether human influences may lead to another major extinction (see "On the web").

In the "Extinction: Is It Inevitable?" activity from the Science Education Resource Center (SERC) at Carleton College, students read an article about past mass extinctions and the current rate of species loss; and then you may choose from various activities, ranging from having students respond to discussion questions about the article to creating an extinction chart (see "On the web"). …

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