Electrified Deep Earth Changing Length of Day

Anne Casselman
for National Geographic News
April 3, 2008

Tiny shifts that make our days milliseconds longer may be due to forces under our feet, a new study has found.

It has long been known that natural phenomena on Earth's surface, such as tides and winds, affect its rotation speed.

Now scientists are investigating how events in a mineral layer at the core-mantle boundary, 1,615 miles (2,600 kilometers) deep, similarly affect the planet's spin.

"The length of a day … is changing due to the interaction between the mantle and the core in the very deep Earth," said study co-author Kei Hirose, a geoscientist at the Tokyo Institute of Technology in Japan.

"This is basically because the bottom of the mantle has very high electrical conductivity."

(Related: "Earth's Core Spins Faster Than Surface, Study Confirms" [August 25, 2005].)

The research appears tomorrow in the journal Science.

Electric Deep Earth

Hirose and his colleagues simulated the physical properties of the deep mantle in their lab to learn more about how minerals in Earth's lower mantle behave.

(Learn what happens inside Earth.)

They squeezed a mineral called post-perovskite between the points of two 0.2-carat diamonds under high pressure.

The researchers then heated the mineral sample with a laser to 4,900 degrees Fahrenheit (3,000 degrees Kelvin).

Continued on Next Page >>


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