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A German scientist by the name of Alfred Wegener,
developed the theory of continental drift in the early 1900's. Wegener
proposed that the continents were once together and had drifted apart.
Most scientist of the time did not accept Wegener’s theory.
But how could this happen? Continents did not
float and easily moved. So more data has to be assembled to explain a
moving crust.
In the 1950's and 1960's instruments were
developed which allowed scientists to study the ocean floor. Their
findings provided Wegener’s theory with explanations that evolved his
theory into Plate Tectonics. Continents did not drift, entire plates
moved! Instruments used to study the ocean floor found large underwater
mountain ranges. Running through the center of these ridges are deep
cracks called rift valleys. These underwater mountain ranges are
called midocean ridges.
Volcanic activity occurs at the midocean ridges.
Lava erupts out of these ridges and spreads to the sides of the rift
valley. The lava hardens, forming new ocean floor. This process is
called ocean-floor spreading. As the new ocean floor moves away from the
rift valley, the continents on top of the ocean floor move also.
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