1. What first led scientists such as Alfred Wegener to suspect that the continents were once joined was the remarkable similarity between the coastlines on opposite sides of the South Atlantic.
2. Pangaea was a supercontinent consisting of all of the present continents together. At around 200 million years ago Pangaea broke up into smaller continents.
3. The evidence that Wegener and his followers gathered to support the continental drift hypothesis was the fit of South America and Africa, ancient climate similarities, fossil evidence, and rock structures.
4. Early in this century, the prevailing view of how land animals migrated across vast expanses of ocean was the idea of land bridges. For example, they thought that other land bridges occurred such as the land bridge that during the recent glacial period lowered sea level and allowed animals to cross the narrow Bering Straits between Asia and North America.
5. The recent acceptance of plate tectonics has been described as a scientific "revolution" because they had made new discoveries that they hadn’t made before.
6. Evidence for a late Paleozoic glaciation in the Southern Hemisphere supports the continental drift hypothesis by the areas that contained evidence of this late Paleozoic glaciation presently lies with 30 degrees of the equator in a subtropical climate.
7. Paleomagnetism can be used to establish the latitude of a specific place at some distant time by the orientation of the paleomagnetism in rocks indicates the latitude of the rock at the time it became magnetized. Imagining a compass needle mounted in a vertical plane, when it is located over the north magnetic pole it points straight down. As it moves closer to the equator the angle of dip is reduced until it becomes horizontal at the equator. From the dip needle’s angle of inclination one can determine the latitude. This is how latitude is established by paleomagnetism.
8. Sea-floor spreading is the process of producing new sea floor between two diverging plates. Hess is credited with the formulating of the concept of sea-floor spreading.
9. Fred Vine and D.H. Matthews related the sea-floor spreading hypothesis to magnetic reversals by every time a new layer of basalt forms it has a different magnetism. Every time a new layer of basalt occurred magnetic reversal occurs therefore it did not form together at the same time.
10. Plate boundaries were first established by the distribution of earthquake and volcanic activity.
11. The lithosphere is being formed at diverging plate boundaries. The lithosphere is being consumed at converging plate boundaries. The production and destruction of the lithosphere must be going on at about the same rate because the Earth is an equilibrium.
12. The oceanic portion of a lithosphere plate subducted while the continental portion is not because the ocean portion has a greater density than the continental portion of the lithosphere.
13. The origin of the Japanese Island is considered similar to the formation of the Andes Mountains by both were formed by convergent plate boundaries. They differ by the Japanese Islands were formed by oceanic-oceanic plate boundaries while the Andes Mountains were formed by ocean-continental plate boundaries. Also, the Japanese Islands are composed of basalt while the Andes Mountains are composed of andesite.
14. At transform faults the lithosphere is neither created nor destroyed. The plates slide past each other. At divergent boundaries plates move apart creating new lithosphere. At convergent boundaries plates move together destroying the lithosphere.
15. Some people predict that California will sink into the ocean. This is not true because at California there is the San Andreas fault where the Pacific Plate is moving northwest past the North American Plate. If this continues the areas west of the fault will become an island off the west coast of the United States and Canada and would eventually reach Alaska. California will not sink.
16. Applying the idea that hot spots remain fixed, the direction that the Pacific Plate is moving while the Emperor Seamounts were being produced was northwest and while the Hawaiian Seamounts were being produced was north.
17. The Himalayas are associated with continental-continental convergent plate boundaries. The Aleutian Islands are associated with oceanic-oceanic convergent plate boundaries. The Red Sea is associated with diverging plate boundaries. The San Andreas Fault is associated with transform plate boundaries. The Andes Mountains are associated with oceanic-continental convergent plate boundaries. Iceland is associated with oceanic-oceanic divergent plate boundaries. Japan is associated with oceanic-oceanic convergent plate boundaries. Mount St. Helens is associated with continental-continental plate boundaries.
Chapter 19: The Ocean Floor and its Evolution(Next)
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