Wandering Continents

[Dover]

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. (See a map of the region.)...cont'd

http://news.nationalgeographic.com/news/2008/04/080407-plate-tectonics.html