Today is 12 October 2009 -- We want to place the age of the earth into a context that students understand

Pretend that you are on a road trip across the United States.  Assume that the age of the earth can be represented by the distance you travel.  For example, at the start of the trip, the earth is a molten glob; by the end of the trip we have reached the present day.  What will we see along the way?  To prepare for our trip, do the following:

1.  Get a blank map of the United States.

2.  On the map, find San Francisco, CA, and New York City, NY.

3.  Draw a straight line between these points. 

4.  The distance between SF and NYC is 2640 miles.  Let this represent the age of the earth, about 4.5 billion years.  If the line on the map is 12 inches, for example, then every inch represents 240 miles AND  375 million years.

5.  Teacher reads from book "Basis of Human Evolution" and identifies points on the map along the line representing milestones in the history of the planet.  (Refer to "ICS Page.")  

6.  As teacher reads, student is to scale the time in terms of miles traveled and mark locations (the "where") the milestones in history (the "when") occurred. 

After doing this, students see that the breakup of the super continent Pangea, 225 million years ago, occurred within 159 miles of the present on our time/distance line which is about 0.66 inch on the map.  (How was this distance calculated?)  

What if we were interested in the events only from 225 million years ago?  We could draw a longer line on the map, or we could "change the scale."  If we change the scale, we let a line on the map represent a different time span.  Try this:

1.  Find Victoria, British Columbia, and Jacksonville, FL, on the map.

2.  Draw a straight line between these points.

3.  The distance between Victoria and Jacksonville is about 3134 miles and represents 250 million years.

4.  Plot the center points of the Permian (250M), the Triassic (200M), Jurassic (135M) and the Cretaceous (65M) years before present on the map.

5.  Measure the length of the line, in cm.

6.  Identify features of the land masses associated with each of these eras.

7.  Write a paragraph about each era, comparing the changes.

8.  Write about how the changes occurred, according to the text.

Students need to know that the time, in terms of distance, can be found by simple ratios or proportions.  Thus:  250M/225M = 22cm/x.  Solving, x = 19.8 cm.