U,Th/He, K/Ar, and U/Xe ages of the depleted mantle source region of oceanic basalts are much less than the age of the earth, showing clearly that the midocean ridge basalt mantle source was not completely degassed and decoupled from the atmosphere early in earth history. Rather, extensive degassing has continued up to at least the last few hundred million years. A stable, layered mantle is not suggested by these data.