Earth Science: Geology, the Environment, and the Universe

Chapter 24: The Mesozoic and Cenozoic Eras

Problem of the Week

To Be or Not to Be: The Sixth Extinction

Mass extinctions have occurred at various points throughout the history of life on planet Earth. Paleobiologists agree that there have been at least five major mass extinctions. The last, and most famous, occurred at the end of the Mesozoic Era in the Cretaceous Period. This is the extinction during which the dinosaurs died out.

Traditionally, when it comes to classifying mass extinctions, they have fallen into two categories based on causation. In the first category, Catastrophism, the mass extinction occurs because of extraterrestrial events, such as meteors, comets, or exploding nearby stars. In the second category, Gradualism, terrestrial agents, such as volcanoes, glaciers, and climate change, causes the mass extinction. There is evidence that the Mesozoic extinction, which killed 85% of the species existing during that period, may have had both catastrophic and gradual causes.

Recently, a third category of mass extinction has been introduced, and is referred to as Non-linear Science of Complexity. In this category of extinction, species to species interactions take place, causing instability in species survival. It appears that this may be what is occurring now, during this, the Cenozoic or Sixth Extinction. It is man who is believed, by most ecologists, to be causing this most recent extinction.

Problem:

As pointed out earlier, during the Cretaceous mass extinction, the one during which dinosaurs died out, it is estimated that 85% of the existing species became extinct. Evidence indicates that this extinction took place over thousands of years.

  1. Given the following information, how long (in years) will it take for the currently occurring extinction to reach the 85% species extinction point?

  2. Assume, for the moment, that both extinctions (Mesozoic and Cenozoic) have ended and are in the past. Which occurred at a faster rate?

Key Information:

  • There are approximately 1.7 million described and named species in the world at this time.

  • 10,000 new species are being discovered each year.

  • It is estimated that approximately 30,000 species become extinct each year.

Glencoe Online Learning CenterScience HomeProduct InfoSite MapContact Us

The McGraw-Hill CompaniesGlencoe