Making The Geologic Time Scale Real

Alan Hoffman
1991 Woodrow Wilson Biology Institute


  1. To have students visualize earth history in a different and concrete way.
  2. To create an awareness of the evolutionary history of plants and animals, including man.


The concept of imagining 5 billion years of time, the approximate age of the earth, is extremely difficult for students as well as for most teachers. This activity is designed to make that concept more concrete for students as well as to give them a new perspective on the history of the earth. Although I do this activity with the study of plants to add greater interest to that topic, it can be done at various times in the school year.


A geological time table, calculators


In class I ask my students to think about 5 billion years of time and to try to express it in a variety of ways such as 5 thousand, million years. After a brief discussion we move out to the playing field. There I tell them to let the 100 yard length of the field represent the 5 billion years of earth history. I have them divide into 7 or 8 groups and each group is assigned a significant occurrence in earth history, such as the appearance of the first photosynthetic cells The group then consults the geologic time table for that date and converts the time into yards distance on the playing field. Having indicated one end zone to represent the beginning of earth history, a member of each group moves the appropriate distance from that end zone to a position on the field. Once all students have assumed their proper positions, they shout out the occurrence in history that their position represents. The spacing dramatically reveals the history of the earth and the short period of time of man's existence.


The students find the activity a refreshing change of pace and come away with a concrete understanding of the tremendous time of the earth and the origin of various species on the earth.

If this is done with a plant unit, it also offers an excellent opportunity to discuss monocots, the grass on the field, and the human intervention involved in the initiation and maintenance of such artificial environments. The place of humans on the time scale surprises most students. This provides an excellent time to discuss man's effects upon the earth in that short time of existence, and more especially in the 20th century.

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