(Geologic) Timing Is Everything!

Part B: The Miocene Timeline

You will now examine the geologic and climate history of Earth over just the past 23 million years. This is time span involved in the studies and research of Expedition 341. Essentially, you are going to take the last 2.3 centimeters of your timeline from Part A and expand it by a factor of 100.

Instead of a meter equaling 1 billion years of time, a meter will now represent 10 million years. Using this scale, what time span will 1 cm of the timeline represent? One millimeter?

The past 23 million years has been divided in three epochs of uneven length—the Miocene, Pliocene, and Pleistocene. Note these epochs and their relative time periods on the graphic above.

Lab Procedure

1. Obtain one set of Miocene Timeline Cards for your group or download them here. (Acrobat (PDF) 48kB Nov2 21) Do your best to put them in sequence from the oldest to the most recent events.

2. Once your group has put the cards in a sequence, obtain a Miocene Timeline Organizer sheet from your teacher and check your sequence. Give yourselves a point for every event that your group has put in the correct order.

3. If any events were out of sequence, reposition them so your cards are in the correct order.

4. Your teacher will gather all the Miocene Timeline Cards and will then redistribute one set, so that your group only has a few cards. On the back of each Timeline Card you are given, write how many million years ago (MYA) the event occurred. This information is on the Miocene Timeline Organizer sheet.

5. With your class, examine the placement of each of the cards on the timeline, and discuss the event's role in Earth's history over the past 23 million years.

  • Figure out where each of your cards belongs on the string.
  • Place each of your cards on the timeline string when your teacher asks you to.
  • Be prepared to discuss your cards and their significance.
  • As appropriate, make comments and ask questions about the other cards and their relationship in the emerging timeline.

Stop and Think

5. Do glacial periods occur at regular time intervals over the past 23-million years?

6. Compare the amount of time that humans have existed to the timing of other events that have occurred through geologic time. Does anything about this timeline surprise you?