MODELING GEOLOGIC TIME

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

Level: 5th through 9th grade

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

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