Chapter 2.docx

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Department
Geology
Course
GEOL 1100
Professor
Xuefeng Liu
Semester
Fall

Description
Chapter 2: Plate Tectonics I. History/Basic background: Continental Drift A. Alfred Wegener, 1880­1930, German meteorologist, proposed “continental  drift” (book “On the Origin of Contents and Oceans). Pangaea  (supercontinent, began to split apart 200 million years ago) B. Evidence to support continental drift:  a. fit of the continents b. paleontology (fossils of the same type were found in different  areas); [rafting hypothesis (animals hang to drifting wood and are  carried across it),  Isthmian hypothesis (land bridge), Island  stepping stones…all supposed to explain it but nothing made sense  but continental drifts] c. geological matches: mountain belts, age similarities, stratigraphic  similarities, igneous provinces d. paleoclimate evidence: ice sheets covered big areas of the southern  hemisphere; same age glaciers are found in different areas C. Objection to continental drift hypothesis: lack of mechanism for moving  continents; Wegener incorrectly suggested continents break through ocean  crust II. Continental Drift and Paleomagnetism­ invisible lines of magnetic force pass  through the planet from one magnetic pole to the other; paleomagnetic rocks  contain “records” of the direction of magnetic poles at the time. Discovered  that magnetic alignment and change in different times (the pole had  wandered). Supports continental drift. III. Seafloor Spreading Hypothesis  A. Harry Hess, Robert Dietz, 1965­ began to map ocean floor, found bizarre  “zebra­like” patterns of magnetism, almost symmetric from center of  ocean ridge B. They proposed oceanic ridges were located above zones of upswelling in  mantle (seafloor spreads laterally from ridge and crest); then, Earth crusts,  allowing for magma to intrude and spread over layers of oceanic crust.  Deep ocean trenches of the seafloor gradually consumed as they descend  into the mantle. C. Evidence to support Hess:  1. Vine­Matthew Hypothesis: magnetic reversals represent poles  switching; lava solidifying at this point becomes magnetized with  opposite polarization they had before (reve
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