MODELING GEOLOGIC TIME

James C. Firebaugh
Virginia Department of Education
P.O. Box 60
Richmond, VA 23216-2060

Anticipated Learning Outcomes

• Students will investigate change through geologic time.
• Students will design, construct and interpret a model of geologic time.
• Students will relate major events in Earth history to the geologic time scale.
• Students will be able to compare and relate the span of Earth history to events of historical time and of the human lifetime.

Materials

• Adding machine paper roll (minimum of 5 meters long)
• Meter stick with centimeter and millimeter gradations

Procedure

1. Review the concept of "scale" with students. The idea that a time scale will be analogous to a map scale should help to "set" the lesson and provide some advance organization.
2. Practice using the scale 1 millimeter = 1 million years (first with single digits, then double digits, and so forth. See attached example.)
3. When students have demonstrated mastery of scale conversion from linear measurement to scale "years," have them convert major events in Earth history from years before present into scale distances. Students should work in groups of two.
4. After a list of events and their scale distances have been formulated, construct the geologic time scale on 5 meters of adding machine paper, beginning with formation of the Earth. Some sample events and their approximate dates are included on the attached page.

Results and Discussion

1. Using their models, generate a discussion with the class around the following questions. A) How does the span of multicellular animal life on Earth compare with the total age of the Earth? B) Animals with backbones? C) Human beings? D) The Space Age?
2. Have students find and record other events on the scale including major periods of extinction and mountain building. Relate these and other events to things such as to the positions of the continents.
3. Have students evaluate the following statement: "Change is the only thing that is a constant."

Variation

Do not provide the scale distances for the students. Let them determine an appropriate conversion and evaluate their results.

 Event Million Years Before Present Distance in Metric Measures The present 0 ______________________ Ice Ages begin 1 ______________________ Earliest human 2 ______________________ Dinosaurs become extinct 65 ______________________ First birds 160 ______________________ East Coast of U.S. undergoes volcanic activity and earthquakes 190 ______________________ Dinosaurs begin to become dominant land animals 200 ______________________ Mammal-like reptiles 210 ______________________ First reptiles 285 ______________________ Appalachians being formed 290 ______________________ First amphibians 370 ______________________ Scorpion-like terrestrial animals 415 ______________________ First vertebrate animals 500 ______________________ First animals with shells 580 ______________________ Multicellular animals evolve 700 ______________________ Oldest known bacteria 3500 ______________________ Inferred age of the Earth 4500 ______________________

Practice examples (use scale of 1 millimeter = 1 million years)

 1 millimeter = _____ million years 5 millimeters = _____ million years 10 millimeters = 1 centimeter = _____ years 100 millimeters = 10 centimeters = _____ million years 1000 millimeters = 1 meter = _____ million years 416 millimeters = _____ years 3 meters = _____ years 100 million years = _____ millimeters 1000 million years = _____ millimeters 1 billion years = _____ meters 428 million years = _____ millimeters