It is the theory that the outer shell of the earth is made up of thin, rigid plates that move relative to each other. The theory of plate tectonics was formulated during the early 1960s, and it revolutionized the field of geology. Scientists have successfully used it to explain many geological events, such as earthquakes and volcanic eruptions as well as mountain building and the formation of the oceans and continents.
Plate tectonics arose
from an earlier theory proposed by German scientist Alfred Wegener in 1912.
Looking at the shapes of the continents, Wegener found that they fit together
like a jigsaw puzzle. Using this observation, along with geological evidence he
found on different continents, he developed the theory of continental drift,
which states that today’s continents were once joined together into one large
Geologists of the 1950s and 1960s found evidence supporting
the idea of tectonic plates and their movement. They applied Wegener’s theory
to various aspects of the changing earth and used this evidence to confirm
continental drift. By 1968 scientists integrated most geologic activities into
a theory called the New Global Tectonics, or more commonly, Plate Tectonics.
Tectonic plates are made of either oceanic or continental
crust and the very top part of the mantle, a layer of rock inside the earth.
This crust and upper mantle form what is called the lithosphere. Under the
lithosphere lies a fluid rock layer called the asthenosphere. The rocks in the
asthenosphere move in a fluid manner because of the high temperatures and
pressures found there. Tectonic plates are able to float upon the fluid
asthenosphere because they are made of rigid lithosphere. (Encarta