Name______Date______Period______

Geologic Clock Activity

One way to understand the relative length of time in Earth’s history is to compare its age to a clock face. Precambrian time goes from 12 noon to about 10:30 P.M. The time span from early human ancestors—more than 5 million years ago—to Homo sapiens covers less than a second on our 12-hour clock!

Standard: SB5.c. Explain how fossil and biochemical evidence support the theory.

Problem: How do different geologic time periods compare?

Materials

-printer papercolored pencils

Procedure

  1. Draw a large circle and mark the 12 positions of a clock face. Use the scale 1 hour = 400 million years ago. Label the 12 positions with the appropriate number of years, starting with the 12 o’clock position = 4800 million years ago, 1 o’clock position = 4400 million years ago, and so on.
  2. Using the geologic time scale provided below, label Precambrian time and the three eras on your clock, along with the approximate time frames in which they occurred. You will be making a pie chart to represent how much time has passed. You should choose a different color for Precambrian time and each of the three eras. Make a key so that your times can be distinguished.
  3. Label the significant events and draw representative organisms on your clock in the appropriate positions, also filling in the approximate time frames they occurred. Then answer the questions on the back of this sheet.

Geologic Time Scale / Beginning / End
Precambrian / 4600 mya / 570 mya
Paleozoic Era / 570 mya / 248 mya
Mesozoic Era / 248 mya / 65 mya
Cenozoic Era / 65 mya / Present
Significant Events / Million Years Ago (mya)
Formation of Earth / 4600
Single-celled organisms / 3800
First stromatolites / 3000
Earliest invertebrates / 570
Earliest fishes / 450
Earliest land plants / 400
First dinosaurs / 240
First birds / 150
Earliest hominids / 4

Analysis and Conclusions

1. What is the geologic time scale?

2. How does the geologic time scale further our understanding about the biodiversity on our planet?

3. What is the oldest era? How long did it last? What was happening during this era?

4. How did the mass extinctions lead way to new forms of life?

5. What have you learned about hominids by looking at your clock?

6. Imagine you time-traveled to the Paleozoic era and had to describe to a friend what you saw. Write at least 5 sentences describing it. Be as creative as possible and write in complete sentences.

7. Which era would you most like to visit and why? Include at least three reasons in your answer. Write in complete sentences!