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2) What is the main idea of theory of plate tectonics? The theory of plate tectonocs stearted in 1915 when Alfred Wegener thougt of"conintal drift"which means tht contients are drifting apart.He thot this because some of the contients looked like they could fit together like puzzle pieces.All of the contients had once been joned together to form a land mass called Pangaea.Panaea is from a greek word that means "all lands".This land mass used to be were Africa is today.People diddn't believe Alfred,but finally in the middle of the 1900's scientists proved that the tectonoic plates do move.This eventualy led to the theory of plate tectonics.

In the 1950's scientists started mapping the sea floor. Everyone thot that the ocean was flat ,but they were supprised to find that the sea floor had lots of underwater mountens (mid-ocean ridges)and trenches.Scientists found out that the the mountains/riges form were there are cracks in the crust.The lava that comes from these craks cools and turns into new sea floor/crust.The old sea floor has to make


 * What are tectonic plates?
 * Give examples.
 * Describe the difference between oceanic crust and continental crust
 * What evidence is there to support this theory? What kinds of evidence led to its acceptance by the scientific community?
 * How do scientists explain how the plates move? About how fast are these plates moving?