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Posted on 04/09/2008 3:28:18 PM PDT by blam
Ancient Imbalances Sent Earth's Continents "Wandering"
Anne Minard
for National Geographic News
April 7, 2008
A new study lends weight to the controversial theory that Earth became massively imbalanced in the distant past, sending its tectonic plates on a mad dash to even things out.
Bernhard Steinberger and Trond Torsvik, of the Geological Survey of Norway, analyzed rock samples dating back 320 million years to hunt for clues in Earth's magnetic field about the history of plate motions.
The researchers found evidence of a steady northward continental motion and, during certain time intervals, clockwise and counterclockwise rotations.
That pattern matches the predictions of a phenomenon known as true polar wander, a theory first proposed in the 1950s.
The theory states that at times Earth's surface mass becomes imbalanced. The continents become dramatically offset from the planet's spin axis and so move rapidly to right themselves.
The new study shows evidence for such motion within the past 320 million years that would have been enough to shift the continents by about 18 degrees latitude.
A change like that today would put Richmond, Virginia, where Mexico City is now.
Island Hot Spots
"I am surprised that our results clearly indicate those episodes of true polar wander at all," Steinberger said.
"Up until now, there wasn't really any agreement in the community about the existence and amount of true polar wander."
That's because the phenomenon has been difficult to distinguish from the slower motion of tectonic plates traveling over the underlying mantle, Steinberger said.
Scientists often use hot spots, relatively fixed thermal plumes of material that rise up from the deep mantle, to track the paths of plates
But geological records of suitable hot spot chains only go back about 130 million years.
A convergence of improvements to geologists' tools paved the way for the team to probe further back in time, Steinberger said.
"We use an updated global plate-tectonic reconstruction and integrate suitable paleomagnetic results from all continents," he said.
The authors were then able to compute the global average of continental motion and rotation as far back as 320 million years ago.
Paleomagnetic records like the ones used in the study can provide a new reference frame for relating surface motions to deep-mantle processes, the authors say.
The study appeared in last week's issue of the journal Nature, and another paper elaborating on the results is in press with Reviews of Geophysics.
Same on Mars?
Given current understanding of Earth's geology, Steinberger is puzzled that true polar wander doesn't show up more often in the planet's history.
"It points toward a long-term stability … which is not expected from fluid dynamics, something which currently geodynamicists try to understand."
Papers published in the journal Science in 1997 and 1998 proposed a much more dramatic polar wander associated with the Cambrian Explosion, a huge diversification in species that shows up in the fossil record beginning around 550 million years ago.
Co-authors of those studies suggested that Earth's continents were thrown asunder relative to the planet's spin axis by about 90 degrees at the time.
One of the researchers, Joseph Kirschvink of the California Institute of Technology, theorized that the shift happened after one or more major subduction zones in the ancient oceans closed down during the final assembly stages of the supercontinent Gondwanaland.
That sent the entire continent rotating at almost a right angle beginning about 534 million years ago, said the authors of the earlier work.
About 16 million years later, North America darted from deep in the Southern Hemisphere to the Equator.
"Even the type of marine rocks deposited on the various continents—carbonates in the tropics, and clays and clastics in high latitudes—agree with these paleomagnetically determined motions," Kirschvink notes on his Web site.
Kirschvink's co-author David Evans, now an associate professor of geology at Yale University, said he's most excited about a relationship between the latest paper and one that came out in Nature last year.
The 2007 study proposes similar continental shake-ups on Mars.
"In the geosciences, we as a community have continued to be impressed by the differences among all the terrestrial planets," he said.
But when it comes to polar wander, Earth and Mars might not be so far apart.
Evans said large igneous regions on both planets—Tharsis on Mars and the central Atlantic magmatic province on Earth—were so massive that they threw their host planets off balance in the distant past.
Does polar wander ever correlate with polar flip flops?
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Okay, yeah, I had a lot of stuff in a file called “Kirschvink”.
Caltech Scientists Find Evidence For Massive Ice Age When Earth Was 2.4 billion Years Old
http://mr.caltech.edu/media/Press_Releases/PR11789.html
Scientists discover that “evolutionary big bang” may have been caused by Earth losing its balance half a billion years ago
Thursday, July 24, 1997
http://mr.caltech.edu/media/lead/072497JLK.html
Texas A&M Oceanographer Challenges Plate Tectonics As Reason For Poles’ Shift
http://www.sciencedaily.com/releases/2000/01/000125053438.htm
Neoproterozoic Paleogeography and Global Climate: SWEAT and the Snowball Earth?
Dave Evans and Joe Kirschvink
http://www.gps.caltech.edu/MagLab/proj_dave.html
Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander
Joseph L. Kirschvink, Robert L. Ripperdan, David A. Evans
http://www.sciencemag.org/cgi/ijlink?linkType=ABST&journalCode=sci&resid=277/5325/541
Snowball Earth
http://www.newscientist.com/ns/19991106/snowballea.html
Did a Quick Spin Pump Up Evolution?
[dead link]
Posted 25 July 1997, 5 pm PST
http://www.apnet.com/inscight/07251997/grapha.htm
Over the last 20 years, geobiologist Joseph Kirschvink of the California Institute of Technology in Pasadena and his colleagues have sought hints of this phenomenon, which has been found on Mars and the moon, by measuring the fossil magnetism in rocks from Australia and North America. They and others have also dated the rocks—parts of the ancient supercontinents of Gondwanaland and Laurentia—by measuring ratios of radioactive isotopes. After analyzing the records before and after the evolutionary explosion, they found that the orientation of the magnetism in rocks from both land masses changed direction by 90 degrees between 534 and 518 million years ago.
UC Riverside Researchers’ Discovery Of Electrostatic Spin Topples Century-old Theory
University Of California - Riverside | April 2, 2003 | Anders Wistrom and Armik Khachatourian
Posted on 04/03/2003 7:28:43 AM PST by forsnax5
http://www.freerepublic.com/focus/f-news/883969/posts
Scientific maverick’s theory on Earth’s core up for a test
SF Chronicle | Monday, November 29, 2004 | Keay Davidson
Posted on 12/05/2004 11:17:28 AM PST by SunkenCiv
http://www.freerepublic.com/focus/chat/1294934/posts
Doubt it. What happens when you shoot a bowling ball with a .22 ? .... Nothing.
A bowling ball is solid throughout. While the Earth has a solid core, it has a very thick layer of magma over that core, with just a thin, broken crust floating on it.
Even the firm, steady push of ice may be enough to prevent a smaller volcanic eruption.
I do not suggest that a six mile ball of rock can muscle an enormous continental plate around, however, it just might be able to “jiggle” it at the point of structural weakness where it meets other plates.
As is demonstrated with crystalline structures, a fault on the surface of the structure creates a multiplicative effect of weakness at the area on the base of the fault. So the effect of that impact might have been like a sharp rap to a pane of glass that had been scored by a glass cutter. It causes a failure along the score which splits the glass in two.
This might have generated all sorts of interesting volcanic effects, from supervolcanoes to something like the basalt floods of Washington and Oregon.
http://tapestry.usgs.gov/features/09michigan.html
A giant incomplete bulls-eye is centered on the state of Michigan. Extending into Illinois, Ohio, Indiana, Wisconsin, and Ontario, this annular pattern outlines the Michigan Basin, a bowl-shaped structure of uncertain origin that contains over 4 km of inward-dipping Paleozoic strata and a veneer of Jurassic sedimentary rocks. This mysterious basin is located in the tectonically less active interior of the continent, between the Appalachians and the Rocky Mountains. It subsided rapidly from Cambrian to Silurian time as it filled with shallow-water marine sediments, some of which host deposits of petroleum, coal, and salt.
Rain of Iron and IceOn November 27,1919, a meteorite fell into Lake Michigan near the Michigan shore. "Residents of Battle Creek, Kalamazoo, South Bend, Grand Haven, and other Western Michigan cities fled from their homes in panic, fearing an earthquake. Houses were shaken, the country was illuminated as by a bright sun's rays, so all-enveloping it was impossible to tell from which direction the flare came, the earth trembled for half a moment and then came a deep prolonged rumbling as of a terrific explosion." (p 159)
by John S. Lewis
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