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(March 2) -- Feeling a bit out of sorts this week? Richard Gross of NASA's Jet Propulsion Lab might have an explanation.
Gross is the scientist who on Monday reported that the massive earthquake that struck Chile on Feb. 27 knocked the Earth off balance. The minuscule shift -- corresponding to 2.76 inches on the surface -- won't produce any noticeable effects. But he notes that larger swings in the planet's axis do happen on a recurring basis and can lead to massive climate change.
Gross explains that the Earth has two axes. The mass is centered around its figure axis, and the planet rotates around its spin axis, which changes its orientation over time.
"The Earth's spin axis varies by three degrees over a 41,000-year cycle," says Pennsylvania State University astrophysicist Darren Williams. These variances in the orientation of the planet affect how sunlight hits the surface, and, when significantly pronounced, they can produce profound results.
This past summer, a group led by geophysicist Peter Clark of Oregon State University reported that cyclical changes in the Earth's rotation and axis contributed to multiple ice ages over the past 2.5 million years. The alterations played a major role in driving global ice levels to a high point around 26,000 years ago, then led them to start dropping 7,000 years later.
What the Chile earthquake did was slightly different, Gross says. When a giant quake occurs, it leads to a redistribution of the planet's mass, which in turn results in a kind of hitch in the figure axis. "The analogy I like to make is the tire on your car," Gross says. "The tire rotates about the axle, but if it's not balanced, it vibrates as it rotates. It wobbles."
As the shift incited by the Chilean quake grabs headlines, the planet is actually still in the midst of a recovery from a much more significant event.
"The Earth right now is rebounding due to the melting of ice from the last ice age," Gross says. Those masses of ice effectively weighed down the surface of the planet, deforming it. As they melted, the mass of the Earth was redistributed, and the Earth isn't quite done settling down. Since 1900 alone, the figure axis has shifted about 33 feet relative to the North Pole -- far more than the effects from the recent quake.
While his NASA report on the earthquake's effect has sparked widespread interest in his work, Gross says that studying the Earth's wobble is consistently exciting. "I've been working in the field for 20 years," he says. "It's never gotten boring."
In Other Earth's-Axis News: Prior Shifts Led to Ice Ages
Mar 2, 2010 – 5:20 PM
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