Geologists have concluded that 80% to 90% of earths continental crust has formed by 2.5 Billion years. But if you look at the geologic map of the world you find that only about 10% of the earths continental crustal surface is labeled "Precambrian." Why?
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After the Hadean period during Archean 80 to 90 % of the earth`s continental crust has been formed comprising chiefly of gniesses, granitoids, various greenstones, metamorphosed igneous and sedimentary rocks and to some extent the the ultramafics (chiefly komatites). But nowadays we see only a little Archean plutons on the continental crust map of earth, the reason for this variation is due to mechanism of earth`s driving forces. Plate tectonics plays the major role in constructing new lands. The older archean crust get underlain by after the formation of new crust by the melting of lower part of the continental crust by the mechanism known as depressurization melting, in which release of pressure lower the melting point of rock and hence formation of new rocks which comes above the surface of earth by volcanism, the major constructive action for continental crust on earth`s take place near the convergent margin where by the action of subduction melting took place in mantle wedge and to some extent in subducting slab, which gives rise to the formation of andesitic composition of rocks on earth`s and it has been believed that this process act as the nucleus for the formation of continental crust on earht....
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