There is as yet no simple answer to the question posed at the beginning of this book: how much is reworked older basement, how much is juvenile? Recent Sm-Nd and zircon Lu-Hf  model studies and the common presence of inherited Archean zircons suggest that it is more complicated than the simple continental growth model advocated in the past. New data are expected in the coming years as a result of international cooperation programmes. That some form of plate tectonics has operated is generally accepted, but whether it is similar to the present processes or forms a transition between Archean conditions and modern tectonics is also still an open question.