Chapter 2 2011 Pearson Education, Inc. 1
Continental Drift: An Idea Alfred Wegener Before Its Time First proposed continental drift hypothesis in 1915. Published The Origin of Continents and Oceans. Continental drift hypothesis The supercontinent called Pangaea began breaking apart about 200 million years ago. 2011 Pearson Education, Inc.
2011 Pearson Education, Inc. Alfred Wegener
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Continental Drift: An Idea Before Its Time Continental drift hypothesis Continents "drifted" to present positions Evidence used in support of continental drift hypothesis: Fit of the continents Fossil evidence Rock type and structural similarities Paleoclimatic evidence 2011 Pearson Education, Inc.
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Matching Mountain Ranges 2011 Pearson Education, Inc.
Paleoclimatic Evidence 2011 Pearson Education, Inc.
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Glacial Striations 2011 Pearson Education, Inc. 10
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The Great Debate Objections to the continental drift hypothesis: Lack of a mechanism for moving continents. Wegener incorrectly suggested that continents broke through the ocean crust. Strong opposition to the hypothesis from all areas of the scientific community 2011 Pearson Education, Inc.
The Great Debate Continental drift and the scientific method Wegener s hypothesis was correct in principle, but contained incorrect details. A few scientists considered Wegener s ideas plausible and continued the search. 2011 Pearson Education, Inc.
Continental Drift and Paleomagnetism A renewed interest in continental drift initially came from rock magnetism. Magnetized minerals in rocks: Show the direction to Earth s magnetic poles Provide a means of determining their latitude of origin 2011 Pearson Education, Inc.
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Polar wandering Continental Drift and Paleomagnetism The apparent movement of the magnetic poles indicates that the continents might have moved. It also indicates Europe was much closer to the equator when coal-producing swamps existed. 2011 Pearson Education, Inc.
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Polar wandering Continental Drift and Paleomagnetism Curves for North America and Europe have similar paths but are separated by about 24 degrees of longitude. Differences between the paths can be reconciled if the continents are placed next to one another. 2011 Pearson Education, Inc.
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A Scientific Revolution Begins During the 1950s and 1960s, technological strides permitted extensive mapping of the ocean floor. The seafloor spreading hypothesis was proposed by Harry Hess in the early 1960s. Even while serving in the U.S. Navy during World War II, Hess was keenly interested in the geology of the ocean basins. In between taking part in the fighting in the Marianas, Leyte, Linguayan, and Iwo Jima, Hess -- with the cooperation of his crew -- was able to conduct echo-sounding surveys in the Pacific while cruising from one battle to the next. Building on the work of English geologist Arthur Holmes in the 1930s, Hess' research ultimately resulted in a ground-breaking hypothesis that later would be called seafloor spreading. 2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
A Scientific Revolution Begins Geomagnetic reversals Earth's magnetic field periodically reverses polarity the north pole becomes the south pole, and vice versa. Dates when the polarity of Earth s magnetism changed were determined from lava flows. 2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
A Scientific Revolution Begins Geomagnetic reversals Geomagnetic reversals are recorded in the oceanic crust. In 1963, Vine and Matthews tied the discovery of magnetic stripes in the oceanic crust near ridges to Hess s concept of seafloor spreading. 2011 Pearson Education, Inc.
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Paleomagnetic Reversals Recorded in Oceanic Crust 2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
A Scientific Revolution Begins Geomagnetic reversal Paleomagnetism was the most convincing evidence set forth to support the concepts of continental drift and seafloor spreading. 2011 Pearson Education, Inc.