Geologic Time Scale Analogy

PURPOSE

To introduce students to the vastness of geologic time and the concept of scale.

BACKGROUND

Unraveling time and the Earth's biologic history are arguably geology's most important contributions to humanity. Yet it is very difficult for humans to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. This exercise begins to make time more "three dimensional" and most importantly, should help you gain a better appreciation for geologic time and our Earth's history.

INSTRUCTIONS

To better understand the concept of geologic time, we will produce a time-scale metaphor to share with the class that is true to scale and reflects some of the important events in the history of the Earth (see the list below). Have fun! Be creative! No metaphor is too silly, as long as your math is correct and your choice has meaning to you.

Choose 3 dates from the list, the arrival of humans (homo sapiens sapiens) and two other dates. Convert the date values to those of your metaphor with correct units. Then write a short (2-3 paragraphs) essay that: (1) discusses why you chose the metaphor you used; (2) shows your math calculations; and (3) discusses what you learned from this exercise including your perspective of where humans fit in the grand scheme of things.

Example: The method used to determine a metaphor value true-to-scale will be similar for all metaphors. Units in the metaphor model can be in time, distance, volume, mass, etc, depending upon what type of metaphor you choose to work with. The general equation used to generate numbers in your metaphor which will be true to scale is:

For example, suppose your metaphor uses distance. Remember, the use of time, volume, or mass in your metaphor would be just dandy. Since we are using a distance metaphor as an example here, a football field with a length of 100 yards will do just fine. To find at what distance along the football field, for example, the "first oxygen" yard mark would be, you would set up the ratio shown below:

So taking the math one step further gives you:

     (2.01 x 10⁹ years)(100 yards) = (X yards)(4.6 x 10⁹ years)

Solving the ratio (for X) will tell you that the "first oxygen" location on the football field would be 43.7 yards away from the goal line of your choice! Determining the location of the other important dates in the history of the Earth is up to you.