Magazine article USA TODAY

Inner Earth Mapping Reveals Lost Sea

Magazine article USA TODAY

Inner Earth Mapping Reveals Lost Sea

Article excerpt

Where do ancient oceans go when they disappear from the face of the Earth? Unlike old soldiers, they don't fade away--they just tumble to the Earth's core-mantle boundary. Located some 2,000 miles beneath the planet's surface, the 180-mile-thick, furnace-like bed of rock is the interface between the Earth's liquid core and the mantle's hard rock. The temperature there is 5,500[degrees]F.

Michael E. Wysession, assistant professor of earth and planetary sciences, Washington University, has discovered and mapped through seismic wave analysis a continental-sized mass of rock that directly corresponds to the location of the ancient Tethys Sea, which disappeared slightly less than 200,000,000 years ago. The two-dimensional image is the highest resolution map yet derived of this part of the inner Earth.

Two hundred million years ago, the continents were fused together in a giant supercontinent known as Pangea. This global alignment placed what is now New York City adjacent to Morocco. When Pangea began to break up, the northern and southern halves, Laurasia and Gondwanaland, were separated by a large body of water--the Tethys Sea. At its eastern end, Tethys was situated between present-day India, Australia, and Asia.

Through plate tectonics--the sliding movement of the Earth's dozen or so plates--the ocean floor supporting the Tethys Sea dipped into the Earth in a process called subduction, where one plate descends beneath another. Over tens of millions of years, the Tethys Sea closed up, the action causing present-day India to collide into Asia, which formed the Himalayan Mountains and the entire Tibetan Plateau. The only surface remnant of the Tethys Sea today is the Mediterranean Sea.

Wysession believes he has found the rest, but it's 2,000 miles beneath the surface. He analyzed 750 digital seismic waves from sophisticated seismographs that have recorded scores of large earthquakes over the past 15 years. …

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