EARTH SYSTEM SCIENCE
WRITING ASSIGNMENT #1 - A PERSONAL METAPHOR FOR GEOLOGIC TIME
Now that you have spent some of your brief time on Earth learning about major events in Earth's history and the expanse of time represented by the geologic and fossil records, it's about time you tried to make some sense of it all! A technique for making Geologic Time tangible in human terms is to create a metaphor for Earth history that compresses geologic time into a scale that the human mind can comprehend. This technique was popularized by the late Carl Sagan in his public television series "Cosmos".
Perhaps the most popular metaphor for Geologic Time is to compress all of Earth history (5.2 billion years) into a single year. To do this, you must equate each second of the year to 143 years of Earth history. How did I arrive at this value? It's easy. First, I need to know how many seconds there are in a year. This can be found using a common mathematical technique called "dimensional analysis":
Notice that all of the terms will cancel except seconds and year, giving me the final answer I need. So, there are 31,536,000 seconds in 1 year. Now, if I want to compress Earth history (5.2 billion years) into 1 year, then each second of that year must equal:
or about 165 years for each second of our "Geologic Year". Now it's just a matter of determining when in this "Geologic Year" major geologic events in earth history have occurred. For example, look at this Geologic Time Scale and the events on it.
In our "Geologic Year", Earth forms at 12:01 a.m. on January 1 (5.2 billion years ago).
The first evidence of life occurs:
8,484,848 seconds later (3.8 billion years ago). When would this be on our "calendar"? Well, 8,484,848 seconds represents
and 141,414 minutes represents:
and 2357 hours represents:
We're almost home! 98 days from 1 January would be April 8. So, in our "Geologic Year", the earliest evidence of life would be found on Earth on April 8. Where do other events occur? See if you can determine these examples using information below:
Signing of the Declaration of Independence = ?
Earliest human fossils = ?
Dinosaurs become extinct = ?
Ouachita Mountains form = ?
First Occurrence of Oxygen in Atmosphere = ?
YOUR ASSIGNMENT FOR THIS WEEK:
Your assignment for this week is to create your own metaphor for Geologic Time using a method similar to the one above. You can use any relation you wish (although let's not use the example above - it's one of the more difficult ones and I've already given it to you!). Use your imagination to think of some interesting metaphor. For instance, you could relate Geologic Time to the length of a football field, or the width of the United States, or any other metaphor you can think of. You will get credit for both your creativity and your ability to make the correct conversions. To help you (and to minimize the amount of time you need to spend on this assignment), write a summary of your metaphor, what the basic conversion factor is, and then show where in your metaphor the following important events would occur:
Signing of the Declaration of Independence (4 July 1776)
Earliest Human Fossils (about 5 million years ago)
Dinosaurs Extinction (about 68 million years ago)
Ouachita Mountains form (about 320 million years ago)
First Occurrence of Oxygen in the Atmosphere (about 2 billion years ago)
First Evidence of Life (about 3.8 billion years ago)
If you find you are having difficulty, don't hesitate to come visit me in my office. I'd be glad to help you organize your methodology. And above all, have fun thinking up something different!
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