Wednesday, April 09, 2008

Earth's Unbalance Sent Continents Wandering

Some interesting developments in the world of geoscience reported by NG. Some new evidence of switches in Earth's magnetic fields found in ancient rock samples seem to support a controversial theory regarding the speed of continental movements in Earth's plate tectonic system.

"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 evidence of this phenomenon is difficult to differentiate from the slower more regular continental movements, but the new analysis appears to show a dramatic shift of up to 18 degrees of latitude taking place over the last 320 million years. Earlier studies from the late 90s also seem to indicate another dramatic shift taking place around 550 million years ago, around the same time as the Cambrian Explosion, the diverse evolutionary period where a fantastic assortment of new life forms appeared.

The researchers of that period hypothesize that one of the planet's major subduction zones, where the ocean seafloor descends into the mantle under the continents, shut down as the continents formed the supercontinent Gondwanaland. The supercontinent then rotated rpaidly at a 90 degree angle and sent North America sprinting to the equator from deep in the southern hemishpere a mere 16 million years later, a relatively short span in geologic terms.

Another item of interest is that the the same theory appears to be applicable to the planet Mars, and the disappearance of what is believed to have been an ocean in the Northern hemishere as that planet's poles wandered.

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