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Honors Marine Science Chapter 1-3 Test (Work in Progress)

Terms in this set (47)

Scientist Alfred Wegner was the first to propose that the continents we know today were once joined into a single supercontinent he called Pangaea. He noted that the edges of the continents fit together much like puzzle pieces. Since he could not explain how these continents traveled away from one another to their current positions, his work was not supported at that time. Since that time, however, evidence to support his theory has continued to accumulate. One of the major pieces of evidence for his theory is the discovery of mid-ocean ridge system in the ocean basins. These ridges are a continuous chain of submarine volcanoes and geologic activity is concentrated around these areas. At these ridges, oceanic crust is separating as molten rock flows from the Earth's interior. New rock is formed in this way and older rock is pushed further from the ridges. Sediments are deeper on ocean floor located away from the ridge, demonstrating that this area has had more time to accumulate these sediments. Rocks are also known to be older moving away from the ridges. Perhaps the strongest piece of evidence to support the activities at the mid-ocean ridges is the discovery of bands, or stripes, on sea-floor rocks known as magnetic anomalies. These anomalies occur because as molten rock cools, magnetic particles in the rocks point towards a magnetic point on the Earth. At different times during geologic history, this magnetic point is magnetic north as it is today. At other times, the field has reversed to create a magnetic south instead. These magnetic anomalies show the direction of this magnetic field at the time they were formed. Therefore, these bands show that the seafloor was not formed all at once, but in stages over geologic time. As new sea floor is created, seafloor in other areas is destroyed as some plates are forced together by this movement. In these areas, trenches are formed. Evidence includes: the fitting together of the coasts of the continents on the opposite sides of the Atlantic Ocean, the similarity of geologic formations and fossils found on the opposite sides, a geologically active mid-ocean ridge running along the central Atlantic between the opposite coasts, bottom sediments that get thicker the farther one travels from the ridge, and rocks on the sea floor on one side of the ridge show magnetic bands that are mirror images of rocks found on the opposite side of the ridge. All of these observations are explained by sea-floor spreading from the mid-ocean ridge.
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