My question is related to a former question about the Earth's early crust. I would like to understand HOW the crust that seems to have been mafic during the Hadean, changed into the other more felsic compositions later. Why this happened? How did it arrive to being so well-separated with the felsic crust under the oceans (I understand that felsic is buoyant and it does not get dense enough, so it can't be under the oceans) But HOW? and WHY?