Scientists have developed a computer model to identify four possible instances of true polar wander in the past. And, they say, true polar wander is happening now.
Scientists based in Germany and Norway have published new results about a geophysical theory known as true polar wander. That is a drifting of Earth’s solid exterior – an actual change in latitude for some land masses – relative to our planet’s rotation axis. These scientists used hotspots in Earth’s mantle as part of a computer model, which they say is accurate for the past 120 million years, to identify four possible instances of true polar wander in the past. And, they say, true polar wander is happening now. These scientists published their results in the Journal for Geophysical Research today (October 1, 2012).
The scientists – including Pavel V. Doubrovine and Trond H. Torsvik of the University of Oslo, and Bernhard Steinberger of the Helmholtz Center in Potsdam, Germany – established what they believe is a stable reference frame for tracking true polar wander. Based on this reference frame, they say that twice – from 90 to 40 million years ago – the solid Earth traveled back and forth by nearly 9 degrees with respect to our planet’s axis of rotation. What’s more, for the past 40 million years, the Earth’s solid outer layers have been slowly rotating at a rate of 0.2 degrees every million years, according to these scientists.
- A geomagnetic reversal, or reversal of Earth’s magnetic field, known to have happened before in Earth history.
- Plate tectonics, which describes the large-scale motions of great land plates on Earth and is thought to be driven by the circulation of Earth’s mantle.
- Precession of the Earth, whereby our world’s axis of rotation slowly moves, tracing out a circle among the stars, causing the identity of our North Star changes over time.
If the volcanoes, land and other masses that exist within the spinning Earth ever became sufficiently imbalanced, the planet would tilt and rotate itself until this extra weight was relocated to a point along the equator.
That’s the theory of true polar wander. It would cause a movement of Earth’s land masses, but for a different reason than the reason the continents drift in the theory of plate tectonics (formerly called “continental drift”). In the theory of plate tectonics, the continents drift because the layer of Earth underlying our planet’s crust, called the mantle, is convective. That is, it circulates, slowly – like water about to boil. In true polar wander, on the other hand, a similar-seeming movement of land masses on Earth’s crust happens in order to correct an imbalance of weight with respect to Earth’s spin.
Read more at : http://earthsky.org/earth/earth-is-undergoing-true-polar-wander-scientists-say