Megabeasts' Sudden Death
Graph and analyze chemical concentrations from ice-core data.
Ice cores can reveal a lot about past climates. To help students understand how scientists use ice cores to learn more about the past, have them do the Secrets in the Ice classroom activity. This activity features actual ice-core field data from the U.S. International Trans-Antarctic Scientific Expedition. Students analyze chemical concentrations of sodium, chloride, and sulfate ions and use additional historic information to date the ice core.
Evaluate the evidence for possible causes of the extinction of Pleistocene mammals.
Explain to students that they will be watching a program about the extinction of giant land mammals (megafauna) in the Americas during the Pleistocene Epoch. Organize the class into two groups, and assign each group one of the following proposed causes of this extinction: "overkill"/overhunting by the Clovis people; or "overchill"/climate change resulting in an ice age. During the program, students should take notes on the hypotheses and evidence supporting the reason for extinction their group was assigned.
Discuss the evidence for possible causes of the extinction of Pleistocene mammals.
Have students meet in their groups to discuss the evidence presented in the program for the group's assigned hypothesis. Group members should refer to their notes as they work. Then have a representative from each group present the hypothesis and supporting evidence for the group's proposed cause of extinction. After both groups have presented, discuss as a class the validity of each hypothesis. Which hypothesis do students think was most supported by evidence? Which hypothesis was least supported? Is there a combination of the two hypotheses that students think may best explain the extinction? If so, what would that be? Ask students to defend their reasoning.
Develop a geologic time line.
Introduce the concept of the geologic time scale. (The geologic time scale is the division of all of Earth's history into distinct blocks of time, characterized by geologic and evolutionary events, and ordered sequentially. They are arranged into eons made up of eras, which are in turn made up of periods, which are in turn made up of epochs.) Then have students use a length of cash-register tape to represent Earth's geologic history. Suggest that students use the University of California Museum of Paleontology time line to identify the different geologic time periods. Have them devise a scale for calculating the length of tape they will need to represent the range of each geologic period as well as the full extent of the planet's geologic history from the Cambrian Period to the current day. (If students use a scale of 1 inch = 10 million years, for example, the tape would be 4.5 feet long.) Then have them measure out the tape and mark each period to scale, noting the names of the time periods and when different types of life evolved.
After students have made their time line, explain to that there have been several major extinctions over the ages. (An extinction is an event in which large numbers of species, including entire genera, die out in a relatively short time.) Assign groups to research extinctions that occurred during the following periods and epochs: Ordovician Period/Silurian (439 million years ago), End-Permian Period (251 million years ago), End-Triassic Period (206 million years ago), Cretaceous Period/Tertiary (65 million years ago), Pleistocene Epoch (13,000 years ago). Ask each group to place a large self-stick note on the time line at the front of the class that indicates the period researched, the types of organisms that became extinct at that time, and possible causes of the extinction. What do students notice about the Pleistocene Epoch extinction? (It occurred in the near-distant past, which is very recent when compared to the other extinctions.)
Research the "sixth extinction."
Point out that some scientists think we are currently living through a sixth extinction period, and that the cause of this extinction is humans and human activity. Have students use the library and/or the Internet to find out why scientists propose this. After students have conducted their research, discuss their findings as a class. What are the competing hypotheses regarding whether an extinction is in progress? What is the evidence supporting the hypotheses? What evidence exists to disprove the hypotheses? How many scientists think this is happening? Compared to scientists' positions on past extinctions, what are the similarities and differences regarding what some scientists think is occurring now?
Denver Museum of Nature & Science—Ice Age
Includes information about megafauna, facts about ice ages, and the causes of ice ages.
Provides a list of 30 prehistoric mammals, with brief descriptions, that shows the animal's size relative to that of a human.
North America—Giant Beasts!
Allows visitors to compare several theories behind the disappearance of North America's big beasts. Find out more about these megafauna, what they looked like, and how they lived.
San Diego Natural History Museum: Fossil Mysteries
Examines the prehistoric record of the San Diego region from the Cretaceous Period to the Pleistocene Epoch. The geologic time line includes descriptions of life forms and extinctions over Earth's history, while the fossil field guide section includes pictures and description of different animals living in the Pleistocene Epoch.
The Sixth Extinction
Explores the "sixth extinction" and includes descriptions of previous extinctions.
UCMP Web Geological Time Machine
Provides an interactive time line chart from the Precambrian Period to the current Phanerozoic, including detailed articles covering ancient life, stratigraphy, localities, and tectonics.
Ice Age Mammals of North America
by Ian Lange.
Mountain Press Publishing Company, 2002.
Includes descriptions of animals such as the giant short-faced bear, scimitar cat, American lion, Florida cave bear, shrub ox, giant camel, stag-moose, giant armadillo, and giant ground sloth. Discusses some potential causes of extinction.
Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America
by Paul Martin.
University of California Press, 2007.
Features paleontologist Paul Martin's examination of Pleistocene ecology and his overkill hypothesis.
Prehistoric America: A Journey Through the Ice Age and Beyond
by Miles Baron, et. al.
Yale University Press, 2003.
Examines America and its wildlife as it looked 13,000 years ago, and includes computer-generated panoramas and images of megafauna based on fossil evidence.
Margy Kuntz has written and edited educational materials for more than 24 years. She has authored numerous educational supplements, basal text materials, and trade books on science, math, and computers.