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Plate tectonics

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Plate tectonics is a relatively new science that describes the surface "crust" of the earth as being broken up into many large and small "plates", which are free to move around independently, as they "float" on the molten mantle. They float because the siliceous material that makes up most of the crust is lighter than the ferrous core and mantle.

When plates collide mountain ranges are often thrust up, like the Himalayas or Rocky Mountains. One of the plates may also be "subducted", or sink down underneath one it is colliding with, as seen at the Marianas Trench. Where plates move apart new material from the mantle rises up to fill the gap, as is occurring at the mid-Atlantic ridge. The surface also is returned back to the mantle in subduction zones. Thus the planet's crust is continually "recycled" to and from the mantle. As a result oceanic crust tends to be relatively young while the continental crust is older. Where plates move laterally relative to one another, major earthquake faults develop. The San Andreas fault is one of the most famous of these.

If a plate slowly moves over a "hot spot" below it in the mantle, a series of volcanoes may result as the hot spot melts through successive sections of the plate. This is how the Hawaiian archipelago was formed - and the "spot" is still "hot", resulting in active volcanoes on the newest island.

While a "new" theory, dating only from the 1970s, plate tectonics is widely accepted for its explanatory and predictive strengths.


[edit] Continental drift

Continental drift is a hypothesis put forward in the early 20th century by German polymath Alfred Wegener[wp] (1880-1930). Based on the observed close fit between the coasts of eastern South America and western Africa, Wegener proposed the idea that the continents shifted position over time. The concept was largely rejected due to a lack of proposed mechanism until the 1960s, when seafloor spreading was discovered at midoceanic trenches; from then on, continental drift was incorporated into the theory of plate tectonics, where internal currents in the Earth's mantle led to gradual shifting of large sections of the crust.

Acceptance of continental drift was delayed due to a number of factors, not the least of which was Wegener's insistence on an impossible mechanism (continents "plowing" through the ocean floor). Also a factor was geologists' avoidance of the evidence that Wegener did have, something now considered to have been a mistake. [1] Another problem was that Wegener was not a trained Geologist by profession but rather a climatologist. If you have any experience studying or working in any field, you might know the reaction an "outsider" gets if they try to overturn all established wisdom.

Continental drift has since been observed using sophisticated positioning equipment placed along major fault lines, as well as satellite observations. As you might have guessed, the continents are not moving very fast, about the same rate as your finger nails grow.

[edit] Pangaea

Animation of Pangaea breaking up.

Pangaea is a "supercontinent" predicted, in a reverse fashion, by plate tectonics. At a point far back in time (ca. 250 million years ago), all of today's landmasses were conglomerated in one large feature. This had the result of allowing land animals to spread over the whole earth, including dinosaurs and mammals, and also produced a giant desert in the center of the continent.

[edit] Where supercontinents come from and go to

Supercontinents form in cycles; many before Pangaea are theorised to have existed and many possible future ones have also been predicted.

  • As the ocean floor between the continents is subducted and disappears, continental plates move together to form supercontinents.
  • They generally break up after a few hundred million years due to changes in mantle convection - the supercontinent acts as a cap and the mantle then overheats and wells up and splits the plate above. The Great Rift Valley in Africa is a current example of this process in action.

[edit] Useful predictions

Fossil areas across landmasses.

Continental drift, and supercontinents such as Pangaea and Gondwana have turned out to be remarkably useful in matching patterns of fossils. The patterns of fossils on currently-separated continents turn out to make lots of sense if those continents were butted up next to each other at the time.

[edit] Peleg

Some creationists think that the statement that the Earth divided in the days of Peleg, as described in Genesis 10, refers to Pangaea, and that the antedeluvian Earth had a single supercontinent, i.e. Pangaea. This is an uber-literal position: even Answers in Genesis thinks the statement refers to the Tower of Babel. [2] No, Answers in Genesis believes the pre-Flood Earth was the pre-Cambrian Rodinia,[wp][3], and that Pangaea simply formed and broke apart during the Flood.

[edit] Saturnism

In the peculiar Saturn Myth offshoot from Immanuel Velikovsky's planetary billiards scenario, it is claimed that, within human memory, Earth was a satellite of Saturn, orbiting in a tidal lock configuration so that the Pangea supercontinent always faced toward Saturn — which glowed as a brown dwarf star, thanks to the Electric Universe. Megafauna apparently flourish in this gravitational environment. Pangea was broken up when the Sun and/or Jupiter crashed into the Saturnian system and Earth ended up orbiting the Sun instead. This idea is nothing if not imaginative.

[edit] See also

[edit] External links

[edit] Footnotes

  1. However, overall, the delay in success of the continental drift theory can be considered an object lesson in what happens when a scientist who happens to be right is a jerk about it.
  2. AIG:In the days of Peleg

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