Why is it that the continental crust is made of granite? (full question inside)?

Great question. Basalt is the original rock from the mantle and is now being recycled on the sea floor on a 200 million year cycle. Basalt enters the ocean at the Mid Ocean Ridge and returns to the mantle at the edges of the granite continental crust. The continental crust never gets recycled into the mantle because it is too light in weight-it floats above the sub-ducting basalt. The continental crust was originally basalt but was transformed by chemical reactions that no longer happen but did until about 3 billion years ago. Prior to ~4 billion years ago granite did not exist. You might not want to use this for school projects because your teacher will question your judgment. But, it is about right anyway.