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The hard plates that form the surface part of the earth are about 100 kilometers thick.These plates include both the earth's curst and the rpper mantle.
Together the crust and upper mantle form the surface plates of the earth.This hard plate floats on the denser material of the lower mantle the way a piece of wood floats on a pond.The plates are carried along by slow flows beneath them.
With an understanding of plate formation,scientists have put forward a new theory for the earth's surface.About 200 million years ago,the plates at the earh's surface formed a super-continent.When this super-continent started to tear apart because of plate movement,it first broke into two large continental masses,with a newly formed sea that grew between the land areas.The southern one included the modern continents of South America,Africa,Australia,and Antarctica.The northern one was made up of North America,Europe,and Asia.North America tore away from Europe about 180 million years ago,forming the Northern Atlantic Ocean.
The plate movement is responsible for earthquakes,volcanoes and the earth's largest mountain ranges.For example,the edge of the Pacific Ocean had been called"Ring of Fire"because so many bolcanic eruptions and earthquakes happen there.Before the1960's,scientists could not explain why active volcanoes and strong earthquakes were concentrated in that area.The theory of plate formation gave them an answer