Moon Is Dragging Continents West, Scientist Says

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Since the hot spots don't move with the crust, they provide reference points against which the movement of the crust's plates can be measured, Doglioni says.

Using this method, he has calculated that the Earth's plates are drifting westward at about 50 to 90 milimeters (2 to 3.5 inches) a year.

Smashing Plates

Another line of evidence, he says, comes from a "profound asymmetry" in the distribution of the Earth's big mountains.

For example, "why are the Andes and the Rocky Mountains only on the eastern side of the Pacific Ocean?" Doglioni asks.

The answer, he says, is that there is more mountain-building power in the eastern Americas.

There, the underground forces of plate tectonics are driving the Pacific plates eastward, toward the continental block, which Doglioni says is being pulled westward by the moon's gravity.

The Pacific plates and the American plates collide head-on, in an impact whose forces are large enough to lift the land far upward, building the great North and South American mountain ranges.

On the other side of the Pacific Ocean the mountain-building force is weaker. That's because the Pacific plate there is also moving westward, essentially rear-ending the Asian continent.

This type of impact produces less crumpling than a head-on collision, and the resulting mountains are correspondingly smaller.

Slippery Layer

The scientist took his theory a step further by attempting to determine what conditions are needed for lunar drag to occur.

He concluded that there must be a thin tier near the top of Earth's mantle (the layer between the Earth's core and its crust) that is less rigid than most earth scientists think it is.

That might be the case if the mantle contains slippery rock layers that slide sideways with relative ease. A recent report in the journal Nature said just that.

The seismologists behind the Nature study appear to have found traces of a slippery layer beneath eastern North America.

"Many Uncertainties" in the Theory

Karen Fischer, a seismologist who co-authored the Nature report, is cautious about Doglioni's study.

"What I would like to see is a quantitative analysis of the westward forcing you see in the paper, compared to other forces acting on the plates," said Fischer, who teaches at Brown University in Providence, Rhode Island.

Other geophysicists are equally skeptical.

"It's creative," said Carolina Lithgow-Bertelloni, a professor of geophysics at the University of Michigan in Ann Arbor. "But there are many uncertainties, and it is extremely hard to test."

She's not so sure about the theory's presumption that the hot spots really are stationary—and neither is Thorsten Becker, an earth sciences professor at the University of Southern California in Los Angeles.

"The hot spots move with respect to each other," Becker said. That motion is slow, but it's enough to make it difficult to argue that hot spots are not truly stationary and therefore are not good reference points.

"Another problem is that most of the hot spots [cited by Doglioni] sit on the Pacific plate," he said.

In other words, they may be appear stationary because they are all on the same plate. Hot spots on other plates may be moving at different rates and in different directions.

Even if lunar drag does exist, Becker says, it is probably impossible for the mantle to contain a sufficiently slippery layer for the moon to be the cause of westward drift.

Still, Doglioni sees exciting, even extraterrestrial, applications for his research.

Lunar drag, he said, "might explain why plate tectonics as we know them on Earth do not occur on moonless planets such as Mars or Venus."

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