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Article: Oceanography: Seafloor Spreading
- Article from:
- American Decades
CopyrightCOPYRIGHT 2001 The Gale Group, Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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OCEANOGRAPHY: SEAFLOOR SPREADING
Liquid Layer
In 1960 the theory of plate tectonics was given a huge boost by the oceanographer Harry H. Hess, who demonstrated his theory that the seafloor was
spreading. The Earth is composed of layers
—
the outer crust, beneath that the mantle, and below that the core. Hess suggested that the mantle, which is eighteen hundred miles thick, has two layers. The deeper layer is solid, he said, which accorded with generally accepted theories about the mantle. But the upper mantle was more like a hot liquid, according to Hess. It pushed up from below. In the deep seafloor rifts, the mantle is close to the surface. It therefore actually comes to the ...