There are many suggested models of continental growth rate which are based on (1) Pb, Sr, and Nd isotopic data from igneous rocks; (2) Sr isotopic ratios of marine carbonates; (3) the constancy of continental freeboard through time; (4) Phanerozoic crustal addition and subtraction rates; (5) the aerial distribution of isotopic ages; and (6) estimates of crustal recycling rates into the mantle \cite{Condie_2005} .