PUZZLING PLATE TECTONICS
Theories concerning the development of landforms and the causes of geologic occurrences have developed through time. Individual ideas combined to result in the modern theory of plate tectonics. Students will create their own supercontinents by fitting modern continents together according to shape and plant and animal similarities.
Instructional Method: Individual Activity
Goal: Show how scientific theories and ideas develop, specifically the development of the theory of plate tectonics.
Objectives: Students will be able to:
Setup: 15 minutes
The plate tectonics theory suggests that Earth's crust is broken into many small pieces that move, and that the plate interactions result in earthquakes, mountain ranges, volcanoes and the separation of continents. It took many years before this theory was accepted as a valid concept. Geologists used a variety of evidence to support their ideas. The following is a history of how scientists developed the theory of plate tectonics, commonly called continental drift.
Each word below links you to a form of evidence used to support this hypothesis.
A French scientist Antonio Snider-Pellegrini (1859) first proposed that all the continents were once connected together during the Pennsylvanian Period (314-280 million years ago). He used identical plant fossils found in coal beds of Europe and the U.S. to support his idea. He attributed the supercontinent break up to the great flood of the bible.
Scientists of the day were very religious. Most of their research was directed toward explaining how God did things on earth, so finding biblical reasons for landforms seemed logical to them. Some people today still rely on biblical texts to explain the world around them.
Another Frenchman, Elisee Reclus (1872), attributed continental movement to random drifting of the continents. His proposal gave no explanation for why the continents floated around, but stated that their collision resulted in mountain ranges and earthquakes and formed voids for oceans.
An Australian scientist, Edward Seuss (1885) described how plants in Late Paleozoic coal beds of India, Australia, South Africa, and South America were all similar, and differed from plants found in northern continents. He proposed a large southern super-continent called Gondwanaland, where the plants were transported by animals over one large landmass
An American, Frank B. Tailor, proposed that gravitational or tidal forces caused by the moon moved continents around. Even though his idea concerning the causes of plate movement were on the edges of contemporary scientific thought, he is credited with the discovery of the Mid-Atlantic Ridge. This ridge or submarine mountain range is a spreading point between two continental plates and allowed the Atlantic Ocean to form between Europe and North America. Scientists today believe that spread at the Mid-Atlantic Ridge caused America to separate from Europe, dissolving a large super-continent called Pangea.
Alfred Wegener, in 1915, is credited with the modern theory of continental drift. He based his theory on a several pieces of evidence including geological, paleontological and climatological factors. He noticed similar rock sequences of the same ages found on separated continents. He also noticed how mountain ranges and glacial deposits match up when continents are pushed together forming a continental jigsaw puzzle. Similar extinct plant and animal fossils are found on continents separated by large distances. All this suggests that the continents were once connected or close together. This large connecting landmass was named Pangea.
A supporter of Wegener named Alexander du Toit found further evidence supporting continental drift by comparing coal bed fossils. He discovered northern continents once formed a large super continent called Laurasia. His evidence includes large fresh water reptiles (Mesosaurus), two land reptiles (Cynognathus and Lystrsaurus), and a Permian plant (Glossopteris). He determined that it would be physically impossible for any of these creatures to be on the different continents unless the continents were in close proximity to each other.
Scientists of the past supported the idea of moving continents, but could not explain the cause of the movement. The theory remained relatively stagnant until the mid 1950's. A boom in paleomagnetic research reignited interest in and generated massive support for the theory of plate tectonics.
Paleomagnetism is a magnetic direction (polar magnetism) recorded in igneous rock at the time the rock solidified. When lava and magma is in its fluid state, small iron minerals in the flow align with the polar magnetism of Earth. When molten rock solidifies, those minerals stay pointing toward the magnetic north. If the rocks moved after that magnetic direction has been locked in, the rock compass does not align with the poles and scientist can determine the original position of the igneous rock along with the amount it has moved over time.
Scientists found that the magnetism in young rocks is aligned with the current north. Ancient rocks vary in orientation and in direction. Scientists determined that instead of magnetic poles wobbling around in different orientations for each continent, the continents moved and the poles stayed in their relative locations.
In 1962 Harry Hess proposed the theory of seafloor spreading. He used information gathered from seafloor basalt studies along the Mid-Atlantic spreading ridge. He suggested that the continents did not float about, but interacted with oceanic crust. Plate interactions formed mountain ranges, earthquakes and volcanoes. He also proposed a mechanism, for driving the movement of plates. This mechanism, known as convection cells, is discussed in greater detail in the Floating Continents activity.
Some continents fit together as though they were part of a continental puzzle. More importantly, much of the fossil, plant and animal life seems to match where the puzzle pieces fit together. In this activity, students will attempt to use the evidence presented to form their own super-continent and see how closely it relates to the most accepted vision of the Pangea Puzzle.
Did your puzzle change shape when you thought about how the plants and animals also fit together? Why or why not? Did everybody's puzzle look the same when you were finished putting it together? What was it supposed to look like? (maybe like the accepted version of Pangea, but it's still just a theory). Did all of your plant and animal evidence match up? What about Australia, why are all the plants and animals so weird? (Australia separated from the other continents first, so it's animals had more time to adapt to their surroundings independent of outside influences). What caused the continents to move in the first place? Are they still moving? What is moving them today?
Younger students - Have the students think about what life would be like on their own version of Pangea and write a creative story about the break up of the super-continent. In this story have them hypothesize what kind of force would have been strong enough to move the continents and how life would change as the continents separated (Time: one day homework).
Older students - have them defend their version of Pangea against the one that is accepted. In truth, we do not know if this accepted version is completely right, and their own version might be more correct. Have the students research the positive and negative aspects of both their own or the accepted version of Pangea. Allow for them to determine for themselves which version is the most likely. (Time: one week, homework).
Included National Parks and other sites:
Utah Science Core:
5th Grade Standard 2 Objective 1,2,3