1. Discuss some of the evidence that Alfred Wegener used to support his idea of continental drift.
2. Describe the theory of plate tectonics.
3. List the evidence and describe the evidence used to support the plate tectonics theory.
4. Discuss mantle convection as a possible cause of plate movements
5. Compare and contrast the push-pull model.
plate tectonics continental drift mid-ocean ridge mantle convection ridge push slab pull
Notes: (8-1 & 8-2)
The Earth's surface is constantly changing. As new land is produced at the mid-Atlantic ridge, old land is being subducted at our continental borders. The movement of land is explained with the acceptance of the presence of many lithospheric plates that continually float and reposition atop of the semi-solid asthenosphere. The theory that explains this process is called plate tectonics. The theory is not a new one. As early as the1500s map makers were beginning to notice that the individual continents fit together like pieces of a jigsaw puzzle. It wasn't until 1912 that Alfred Wegener first proposed an acceptable hypothesis (continental drift) as an explanation.
Wegener’s continental drift hypothesis:
The theory of continental drift simply stated that continents drifted from one location to another over time. Wegener noticed that the coasts of South America and Africa seemed to fit together like a puzzle. Upon further investigation he noticed the following clues that he used to support his hypothesis.
Fit of S. America and Africa
Fossils - Mesosaurus & Glossopteris found on similar areas on both continents
Rock structures - mountain ranges seemed to match up
Climate clues - ferns found in the artic
Main objection to the hypothesis was the inability to provide a mechanism
In the 1950s & 1960s technology had sufficiently advanced and the theory of plate tectonics became more widely accepted.
The theory was based on the movement of 20 rigid lithospheric plates.
Lithospheric plates contain the continents and extend out into the ocean basins.
The plates move atop of the semi-solid asthenosphere
The theory was more complete than the continental drift hypothesis as it was focused on the mechanism of plate movements as well as the outcome. Observations supporting plate movements included:
Mechanisms of Plate Tectonics
Evidence That Supports Plate