When did the Earths continental crust begin to form?
Continental crust developed after the initial mafic to ultramafic crust. Continental crust is sialic or felsic (such as granite). Dominated by light-colored minerals such as quartz and feldspar. Felsic crust began forming around 4.4 billion years ago. Felsic crust formed in subduction zones where descending slabs of crust partially melted. The early-melting, less dense components of the melt rose to the surface where they cooled to form continental crust. One of the oldest dated felsic Earth rocks is the 4.04 billion year old Acasta Gneiss from northwestern Canada. Dates are from zircon grains in tonalite gneisses. (Tonalite gneiss is metamorphosed tonalite, a rock similar to diorite, with at least 10% quartz). The Amitsoq Gneiss from Greenland is another old tonalite gneiss (3.8 b.y. old). Patches of old felsic crust have also been found in Enderby Land, Antarctica (3.9 b.y. old). A 3.46 by old fossil soil zone (or paleosol) associated with an unconformity in the Pilbara region of Aus
