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. Perhaps we can only hope that students catch glimpses of our rich
geologic heritage, particularly when most of our teaching is done in a
classroom and not in a field setting. This exercise begins to make time more
"three dimensional" and most importantly, students gain a better
appreciation for geologic time and our Earth's history.
Instructions
To better understand the
concept of geologic time, have students produce a timescale 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 list on the following page). Write an
explanation paper that: (1) discusses why you chose the metaphor you used; (2)
shows your math calculations for all events; and (3) discusses what you learned
from this exercise including your perspective of where humans fit in the grand
scheme of things. Have fun! Be creative! No metaphor is too silly, as long as
your math is correct and your choice has meaning to you.
Example:
The method used to
determine a metaphor value truetoscale 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:
Known age
of past event (years before present) 

UNKNOWN
Time scale metaphor 
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:
Known
first oxygen (2.01 x 10^{9} years) 

UNKNOWN
(first oxygen on football field) 
So taking the math one step
further gives you:
(2.01
x 10^{9} years)(100 yards) = (X yards)(4.6 x
10^{9} 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.
Some Important Dates in the History of
the Earth


Include main events from pp 84 (evolution
of life), 88 (Pangea events) & 93 (5 past mass
extinctions) not already in this list
