6. Geologic Timelines - Lesson Plan

Lesson Plan

  1. As students trickle into class, direct them to the front of the room and have them add an arrow or dot to the timeline on the board. (If this format is too chaotic for your classroom situation, add labels and tick marks every 200 million years or so and have students write down their numerical guesses on a sheet of paper in their seats.)
  2. When all students have made a guess, briefly discuss their hypotheses. In particular, ask them about their reasoning behind their guesses.
  3. Distribute the geologic time scale handouts. Give students a moment to see if they can determine how many years ago the Earth and solar system formed (4,570 million or 4.57 billion years ago). Allow the student that first discovers this information to explain how s/he figured out the answer. Point out how the geologic time scale has the most recent events on the top and the most ancient events on the bottom, just like rock layers.
  4. Ask students to find out when dinosaurs roamed the Earth. This time, ask them to tell you not only how many million years ago but also during what eon, era, and periods dinosaurs lived. Again, allow the student who discover this information to share how s/he read the answer. Point out how the eon, era and period can be determined by the first 3 columns in the table.
  5. Ask students to find out when the first humans appeared. Is this a long time ago compared to the entire history of Earth or a short time?
  6. Give students a brief overview of the 4 major eons and the types of life that were present in each. Refer to the geologic time scale frequently to reinforce how to read information from the table.
  7. Ask students which of these eons was the longest? Which was the shortest? How do you know? Point out that the timescale is not broken into even chunks of time. That some eons are longer than others, just as some eras are longer than others and some periods are longer than others. Thus, while the geologic time scale is good for finding information, it’s not an accurate way to visually see how long one chunk is compared to another.
  8. Tell students that they will now create a timeline representing the most recent eon, the Phanerozoic. On the board write “1 millimeter = 1 million years; 1 centimeter = 10 million years”. Show students a strip of adding machine paper and hold a meter stick up next to it. Model for them how to keep the meter stick in the same place, with one end of the paper aligned with the 0 mark, and how to mark off boundaries between the eras and periods and label each mark with the number of millions of years ago that mark represents.
  9. Give students their own adding machine tape and a meter stick. Remind them with your own set up how to mark off the boundaries between the periods using the meter stick and their time scales. Once they have the general idea, wander around the classroom helping individuals that are having difficulty.
  10. Once the time boundaries are marked off, have students identify each period and write in the name of the period and one of the major biological events that happened in that period.
  11. If you have time, have students color their time scales. I had my students color each of the eras a different color to visually link the periods in the same era together. Alternatively, you could color each period a different color.
  12. When students are done or 10 minutes before the end of class, have a student that is finished hold up their timeline. Tell students that you created a timeline that includes all of Earth history, from when the Earth and solar system formed until today. Match the “today” end of your rolled up timeline with the “today” end of your student’s timeline. Unroll yours behind or below your student’s. When you reach the end of the Paleozoic, have a student come up to hold that section and briefly review the major events in that eon. Continue unrolling and stop again at the end of the Archaen eon to have a student hold that section and to review the major events. Finish in the same fashion with the Hadean eon.
  13. With the remaining time, give students one or two analogies as “food for thought” to depart class with.

Geologic time as a calendar year:

  • Imagine that the geologic time scale is contained in 1 calendar year (each second is around 146 years). January 1 is 4.6 billion years ago.
  • The oldest known rocks are formed in early March
  • The first forms of life (bacteria and algae) are preserved as fossils in late March
  • The first multi-celled creatures (seaweed) appear on September 3
  • Phanerozoic Eon (most recent eon) begins on November 11
  • Reptiles appear on December 5
  • The first mammals appear December 14
  • Dinosaurs go extinct December 26
  • The first hominids (human-like ancestors) appear at 5 PM on December 31 (7 hours before midnight)
  • The first modern humans (Homo sapiens) appear at 11:48 PM on December 31 (12 minutes to midnight)
  • The last glacier receded at 11:58:45 p.m. on December 31 (1 minute and 15 seconds before midnight)
  • Written history begins at 11:59:30 on December 31 (30 seconds before midnight)
  • Columbus lands in the Americas 3 seconds before midnight
  • You were born 1/10th of a second before midnight


Geologic time as the distance from Los Angeles to New York City:

  • The distance from LA to NYC is approximately 4500 kilometers (km). Therefore, each kilometer represents one million years of Earth history. Look at a map of the United States. Start the geologic time journey in LA.
  • Precambrian would last until Pittsburgh
  • Paleozoic would be entirely in Pennsylvania
  • Mesozoic would get us to New Jersey, only 66 km from NYC.
  • The most recent Ice Age ended about 10,000 years ago. 10,000 years = 1/100 of a million years = 10 meters.
  • The past 2000 years of history would be represented by a sidewalk (2 meters)
  • A human lifespan would be half of the width of a curb (100 millimeters)