Plate Tectonic - Plate Tectonics (6)
Post Lab 

   
OBJECTIVES:
  • Comparing continental drift with plate tectonics.
  • Observing the movement of Earth's crust.
VOCABULARY:
  • continental drift
MATERIALS:
  • worksheet

Students investigate plate movements.


The positions of the continents about 300 million years ago. 

BACKGROUND:

One of the first observations used to suggest that the outer portion of the Earth is mobile is the fit of the continents, particularly the west coast of Africa against the east coast of South America. This observation predates plate tectonics. It was first noticed in the 18th century, and proposed by a German scientist, Alfred Wegener in 1912. Wegener called his theory called "continental drift", referring to the apparent movement of continents alone. However, "continental drift" is a historical term, that may give the wrong notion to children. We now know It is not the continents that move, but the plates, in which the continents are embedded. South America and Africa were once together, but were split apart by the formation of a diverging plate boundary. This is confirmed by matches between the rocks and fossils of the two continents. Plate motion, not continents drifting, explains this. The two continents are still moving away from each other today.

Even through it has been established that the plates, and thus the continents, have moved through time, many unanswered questions remain on how the plates move, as well as where they have been in the past. In this post lab, the students will examine maps which show the positions of the plates and continents at several times over the past 510 million years. The evidence for these locations is difficult to understand, but real. The maps show only the continental parts of plates. The remainder, composed of oceanic crust, is destroyed through time by subduction and collision at convergent plate boundaries.

Several websites have excellent images of past plate configurations. Two that are particularly good are;
 
http://www.ucmp.berkeley.edu/geology/tectonics.html/ - The plate tectonics page at the University of California, Berkeley Paleontology museum. Good animations of plate motions, and explanations for how it works.
  
http://www.scotese.com/ - The Paleomap Project - detailed plate location reconstructions for the past 650 million years. Also simple animations of plate motion.

PROCEDURE:

  1. Explain to the students that plate motions have made the continents move through time. Make sure that they understand that the plates move, and the continents ride on their backs.
      
  2. At the elementary school level the reason why geologists feel that the maps are accurate cannot be explained effectively to students. Just try to have fun with your class, and try to understand the differences between the maps. Here are some suggested activities and questions:
      
    1. Have your students chart the differences from one time frame to another.
    2. See if some continents have been at the equator at some point in the past. (Yes, North America, 510 million years ago).
    3. Would the rocks on a continent record a different climate if the continent was in a different place on the Earth? (Yes)
    4. Have your students make a "flip movie" by placing the pictures in the chronological order. If you wish to do this activity, we suggest you print the maps on thicker paper.
    5. If you have studied fossils in your class, you might want to discuss whether or not the fossils in rocks can provide any clues about the continents' past positions. (Yes, for example in Antarctica, paleontologists have found fossil trees. Looking at the maps, when could this have happened? 500-520 million years ago.)
    6. Which continents have moved a lot? North America, Australia
    7. Did we always have the Pacific Ocean and Atlantic Ocean? No
    8. Color one continent one color, and trace it throughout the different maps This makes it easy to identify.
    9. Cover one of the maps on each sheet and see if your students can recreate what the missing map should look like.

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