Extreme models for continental growth propose rapid growth early in the Earth's history, followed by extensive recycling of continental sediment back into the mantle \cite{Reymer_1984} (curves 1 and 2, Fig. 4). On the opposite extreme models are based mainly on the geographic distribution of isotopic ages on the continents (Hurley Rand 1969). These models propose that continents grew slowly in the Archean and rapidly after 2 Ga (curve 5, Fig. 4). Other models are represented to between these two models. The distribution of U-Pb zircon ages coupled with ND isotopic data suggest two major peaks in juvenile production rate, at 2.7 Ga and 1.9 Ga (Fig. 5).  

Role of Recycling

The distribution of juvenile continental crust ages (Fig. 5) is a function of two factors: the rate of continental extraction from the mantle, and the rate of the recycling of continent back into the mantle. The difference between these two factors is the net continental growth rate, which can be considered as the preservation rate of continental crust.