TELLING THE history of the earth requires placing events in sequence so that reference can be given to the relative and/or numerical time at which each event occurred. This helps to make sense out of the enormous expanse of time that has elapsed since the origin of the earth. This activity will help students to understand the methods used by geologists in creating the Geologic Time Scale.

1) Students will place events in sequence and assign relative times to each event.
2) Students will gain an understanding of relative and numerical time.
3) Students will become familiar with the methods used by scientists to develop the Geologic Time Scale.

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1) Each student will need: A copy of the worksheet Events in Your Life.
2) A copy of the sheet Your Personal Time Line. (click here to download a pdf version)


Instruct the students as follows:
1) Look at the events listed on the sheet entitled Events in Your Life. Arrange these events in order, by placing the number 1 in front of the event that occurred first in your life, a number 2 for the second, etc.

2) On the worksheet entitled Your Personal Time Line, you will be writing these events in order in the third column, Sequential Time, but you will be writing them so that the most recent event is at the top of the list and the event that occurred first is at the bottom of the list. (Students do not need to write out the entire event. For example: "When you learned to walk" could be written simply as "Learned to Walk".)

Your completed list is now similar to what a geologist might refer to as a Sequential Time Line.
a) You can use your own sequential time line to describe events in your life. For instance, I learned to ride my bike after I learned to walk but before I started second grade. Have the students describe events in their lives in a similar way.
b) Now, using sequential time, how could you describe when Tyrannosaurus rex roamed the earth?
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3) Return to your time line worksheet. In the middle column entitled, Numerical Time, place a zero by today's date. Then think of the number of years ago each event happened. Write these numbers in the column in front of each event. If you can't remember exactly, try to guess and round off to the nearest whole year. These numbers are the numerical ages of the event and make up a numerical time line.

Now you can use both the sequential and the numerical information to describe events in your life. Using both of these, describe when you started kindergarten. An example might be: I started kindergarten four years ago, after I learned to walk but before I lost my first tooth.

4) Now you are going to divide the events into two time intervals. Draw a horizontal line above the last event that happened before you started kindergarten. Now every event above the line took place after you started kindergarten and every event below the line took place before you started kindergarten. In the first column entitled Time Interval, write the word Preschoolian below the line and the word Schoolian above the line. This worksheet now resembles a complete time line for the events in your life. They are in the proper sequence. They have been given a date in time. And they have been grouped into two major event groups.

See if you can describe a single event using the information in all three columns. An example: I started Kindergarten at the beginning of Schoolian time, four years ago...

Think of another event which has occurred in your life. For example, the first time that you tasted pizza. You probably cannot remember the exact year when that occurred, but you probably can place it between two events which you can remember. Therefore, you would know its relative time. How could you give it a numerical time?

This activity provides a good introduction to the Geologic Time Scale which has been arranged (and developed) in a similar manner. If it is used by older students, it is possible to change the Events and to divide them into three time intervals, such as Preschoolian, Gradeschoolian, and Postgradeschoolian.
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1) Compare the Personal Time Line to the actual Geologic Time Scale to note similarities and differences.
2) Draw a comparison to the correlation of rock layers and the fossils they contain to a relative time scale. Consider an introduction to the importance of index fossils.
3) Follow this activity with actual events that occurred in Geologic History and/or the development of Time Lines.
4) Follow this activity with What Came First?

This activity has been adapted from How Long Is a Long Time? published by the National Association of Biology Teachers.