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Name: Loretta G.
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: August 2, 2004

What evidence is there proving Earth is broken into plates and are there 12 plates?

According to the US Geological Survey, there are seven major continental plates:

-North American
-South American

There are also several smaller plates and sub-plates, including:

-Juan de Fuca

So, there are seven to fourteen plates depending on whether the smaller plates are defined as independent or as sub-plates of the major ones. Although plate tectonic theory is supported by a variety of observations, the concept of plate tectonics was not widely accepted until the 1960's. The item that persuaded many geologists was the discovery of residual magnetism in the sea floor along with the understanding of periodic agnetic pole reversals through geologic time. An Internet search on the term Plate Tectonics" will yield a variety of excellent sites that have detailed explanations of the plates and the observations that support the plate tectonic theory.

The University of California, Berkeley's Museum of Palentology has an explanation of the history of plate tectonic theory at:

Andy Johnson

There are 7 major and 13 minor plates. These plates are lithospheric plates which consist of the crust and part of the upper mantle.

Many earthquakes, volcanoes and mountain ranges are the result of lithospheric plate motion.

The Oceanic Ridge System, essentially an underwater mountain range, provides evidence of the sea floor spreading or moving. As a result of this motion, lithospheric plates move away from these spreading centers and are either subducted (forced to sink) elsewhere or collide with other plates causing mountains to form like the Himalayas.

Much more information can be found on this subject by searching for "plate tectonics."

Steven Miller

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