Difference between revisions of "Plate tectonics"

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-{{merge from|Continental drift}}
-'''Plate tectonics''' is a geological model of the movement of [[continental plate]]s around the surface of the [[Earth]].
-== Developing the Theory ==
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-Continental drift was hotly debated off and on for decades following Wegener's death before it was largely dismissed as being eccentric, preposterous, and improbable. However, beginning in the 1950s, a wealth of new evidence emerged to revive the debate about Wegener's provocative ideas and their implications. In particular, four major scientific developments spurred the formulation of the plate-tectonics theory: (1) demonstration of the ruggedness and youth of the ocean floor; (2) confirmation of repeated reversals of the Earth magnetic field in the geologic past; (3) emergence of the sea floor-spreading hypothesis and associated recycling of oceanic crust; and (4) precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges.
-== Ocean floor mapping ==
-About two thirds of the Earth's surface lies beneath the oceans. Before the 19th century, the depths of the open ocean were largely a matter of speculation, and most people thought that the ocean floor was relatively flat and featureless. However, as early as the 16th century, a few intrepid navigators, by taking soundings with hand lines, found that the open ocean can differ considerably in depth, showing that the ocean floor was not as flat as generally believed. Oceanic exploration during the next centuries dramatically improved our knowledge of the ocean floor. We now know that most of the geologic processes occurring on land are linked, directly or indirectly, to the dynamics of the ocean floor.
-"Modern" measurements of ocean depths greatly increased in the 19th century, when deep-sea line soundings (bathymetric surveys) were routinely made in the Atlantic and Caribbean. In 1855, a bathymetric chart published by U.S. Navy Lieutenant Matthew Maury revealed the first evidence of underwater mountains in the central Atlantic (which he called "Middle Ground"). This was later confirmed by survey ships laying the trans-Atlantic telegraph cable. Our picture of the ocean floor greatly sharpened after World War I (1914-18), when echo-sounding devices -- primitive sonar systems -- began to measure ocean depth by recording the time it took for a sound signal (commonly an electrically generated "ping") from the ship to bounce off the ocean floor and return. Time graphs of the returned signals revealed that the ocean floor was much more rugged than previously thought. Such echo-sounding measurements clearly demonstrated the continuity and roughness of the submarine mountain chain in the central Atlantic (later called the Mid-Atlantic Ridge) suggested by the earlier bathymetric measurements.
-In 1947, seismologists on the U.S. research ship Atlantis found that the sediment layer on the floor of the Atlantic was much thinner than originally thought. Most scientists had previously believed that the oceans have existed for at least four billion years, so therefore the sediment layer should have been very thick. Why then was there so little accumulation of sedimentary rock and debris on the ocean floor? Their answer to this question, which came after further exploration, would prove to be vital to advancing the concept of plate tectonics.
-In the 1950s, oceanic exploration greatly expanded. Data gathered by oceanographic surveys conducted by many nations led to the discovery that a great mountain range on the ocean floor virtually encircled the Earth. Called the global mid-ocean ridge, this immense submarine mountain chain -- more than 50,000 kilometers (km) long and, in places, more than 800 km across -- zig-zags between the continents, winding its way around the globe like the seam on a baseball. Rising an average of about 4,500 meters(m) above the sea floor, the mid-ocean ridge overshadows all the mountains in the United States except for Mount McKinley (Denali) in Alaska (6,194 m). Though hidden beneath the ocean surface, the global mid-ocean ridge system is the most prominent topographic feature on the surface of our planet.
-== Magnetic Striping and Reversals ==
-Beginning in the 1950s, scientists, using [[magnetism|magnetic]] instruments (magnetometers) adapted from airborne devices developed during [[World War II]] to detect [[submarine]]s, began recognizing odd magnetic variations across the ocean floor, showing reversals in the Earth's magnetic field over it's history. This finding, though unexpected, was not entirely surprising because it was known that basalt -- the iron-rich, volcanic rock making up the ocean floor-- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. This distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these newly discovered magnetic variations provided another means to study the deep ocean floor.
-==Biblical View==
-{{Bible quote|And God said, "Let the water under the sky be gathered to one place, and let dry ground appear." And it was so. God called the dry ground "land," and the gathered waters he called "seas."|book=Genesis|chap=1|verses=9-10}}
-This verse was one factor leading creationist [[Antonio Snider]] to propose in 1859 that the continents had originally been one and had moved apart.
-{{Bible ref|Genesis|10|25}} says of [[Peleg]] that "in his time the earth was divided".
-Some [[Young Earth creationism|creationists]] have seen this as referring to the tectonic plates moving<ref>Dawson, James P., [http://www.jpdawson.com/pelgnet/pelchap1/PELCHAP1.html In the Days of Peleg], 1998.</ref>.
-However, many creationary scientists consider this verse to be referring to the division of the people at the [[Tower of Babel]], and not to plate tectonics.
-Instead, they propose that most of the continental plate movement occurred during the [[flood geology|great flood]].
-Dr. [[John Baumgardner]], a geophysicist then with the Los Alamos National Laboratory, developed a sophisticated 3D computer model of plate tectonics, and believes that his model works best as a rapid process during the Flood.<ref>Batten, Don, et. al., [http://www.creationontheweb.com/images/pdfs/cabook/chapter11.pdf What about continental drift?] Chapter 11 of the Creation Answers Book, 2007.</ref>
-The magnetic stripe reversals are believed by mainstream scientists to have occurred over millions of years.
-However, creationist Dr. [[Russell Humphreys]] predicted that magnetic reversals would be found with time frames of days or weeks, from having occurred during the Flood.
-In an example of a successful creationists prediction, scientists subsequently found magnetic reversals that had taken place over the space of 15 days.<ref>Snelling, Andrew A., [http://www.creationontheweb.com/content/view/1233/ Fossil magnetism reveals rapid reversals of the earth’s magnetic field], ''Creation'' 13(3):46–50, June 1991.</ref>
-==References==
-{{reflist|2}}
-[[category:geology]]

Difference between revisions of "Plate tectonics"

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