Geologic Time
Introduction:
“The crust of our earth is a great cemetery, where the
rocks are tombstones, on which the buried dead have
written their own epitaphs.”
Louis Agassiz, a Swiss-born naturalist and author who live more than a century
ago (1807-1873), originally wrote the words quoted above. Although much of geologic
time was without life, geologic interpretation often involves the observation and
interpretation of the fossils of living things that did exist. The fossil evidence often tells
its own story an in the process presents valuable information not only on the appearance
of different kinds of life but on the evolution of the Earth itself. The story of the geologic
and biologic evolution of the past is found among the details of large-scale rock structure
and the smaller fossils buried in the rocks.
The geologic time scale is a type if classification system that has been affected by
the changing interpretation and classification of fossil evidence and geologic events. The
time scales is a model that organizes many years of evidence and interpretation and will
help you understand the story the Earth itself has written.
Geologic time has been divided into eras, periods, and epochs based on various
changes, such as extinctions, seen in the fossil record of life. Geologic events, such as
orogenies (periods of mountain building), have also been used to mark divisions with the
time scale. You will make a scale model to describe the duration or length of the
different eras, periods, and epochs that cover progressively shorter periods of time.
Objective: After you have completed this investigation, you should be able to:
1. Construct a scale model to illustrate the time of occurrence of geologic events.
2. Compare the time intervals between carious geologic events.
Materials:
5 meters of paper tape
meter stick
ruler
pencil
Earth Science Reference Tables
masking tape
colored pencils
scissors
Procedure:
1. For this investigation, the scale is 1 mm = 1 million years. Using this scale
complete page 1 of the Report Sheet. When finished with page 1 you must have
your teacher check it before you continue.
2. On the second page of the Report Sheet convert each of the Distance on Scale to
centimeters (cm) and (m). Again, check with your teacher before you continue.
3. Measure and cut off exactly 5.25 meters (5 meters and 25 centimeters) of paper
tape.
4. Stretch out the adding machine tape on your table. Using a ruler, measure 25
centimeters from the right end and draw a straight line across the tape. On the
right side of this line, label “TODAY”.
5. From the line labeled “TODAY”, draw 5 more lines, exactly 1 meter apart. Label
the first line (on the right side of the line) “1 BILLION YEARS AGO”. Label the
second line (always on the right side of the line) “2 BILLION YEARS AGO”.
And so on. The fifth line, then, will be labeled “5 BILLION YEARS AGO”.
6. Plot each event listed on pages 1 and 2 of your Report Sheet on the paper tape.
7. Label BOTH the number of years ago and the event.
8. Using the Geologic Time Line that you have created, complete the questions on
the Report Sheet.
9. Roll up your paper tape. On the outside, write the names of you and your partner.
Fasten with rubber band or tape and hand in to the teacher.