This internet exercise will examine the nature of geologic time and the expanse of Earth's history. For many students, the scale of geologic time is never fully grasped.

A popular device for making geologic time comprehensible is to create a metaphor for geologic time where Earth's history is compressed into a more reasonable time interval, such as a single calendar year.

Then, important events during Earth's history are placed at appropriate corresponding dates on the calendar. For example, the beginning of the Cambrian Period (551 million years ago) occurs approximately 88% into our geologic year. This places it in mid-November.

For this exercise, visit theGeologic Time Calculator. This web site removes the drudgery of creating a geologic time metaphor by providing you with some ready-made metaphorical conversion factors. Spend some time familiarizing yourself with the operation of the calculator and answer the questions below related to geologic time and the geologic time scale.

1. Set the calculator to 365.25 days (that is, 1 year).

2. Using the calculated data, determine the calendar dates of the geologic time intervals that are presented. Note that the answers are generally given in days such that an answer that indicates an event occurred 30 days from the beginning would be placed on 31 January.

During each generation, people often have a collective memory of an historic event and relate that event by remembering what they were doing at the time. During the last century, these events included Pearl Harbor, the assassination of John F. Kennedy, the Apollo 11 lunar landing, and the Space Shuttle Challenger catastrophe. For the present generation, there is little doubt that the events of September 11, 2001 will enter this collective memory.

3. Now create your own metaphor for geologic time. Determine your age in days by dividing your age by 365 and adding the appropriate number of days for the present year to that value. Now, enter your age in days into the box labeled "Imagine that the entire history of the earth is" and make sure you pick "days" in the adjacent box. Then use the results from the calculator to determine how old you were at each of the major divisions of the geologic time scale.

4. Where were you and what you were doing at each of the major divisions of the geologic time scale? You may be surprised at how much or how little you remember of Earth's history from this exercise!