Continental freeboard, sedimentation rates and growth of continental crust

Abstract

To understand how the Earth has evolved requires a model for the timing and nature of the formation of the continental crust. Of the two contrasting models, the first and most popular is that the continental crust of the Earth has grown throughout geological time. Models of linear or exponential increasing growth with time1,2 are not currently accepted, and it is now generally held that much of the crust was in place by 2,500 Myr with a particularly active period of crustal growth and differentiation between about 3,200 and 2,500 Myr (refs 3–13). The second model argues that the present mass of the continental crust formed very early in Earth history (>4,000 Myr) and has subsequently been recycled through the mantle in a steady-state fashion such that the mass of the crust has not changed during most of Earth history14–16. Resolving these conflicting views is not simple because interpretation of the isotopic evidence is non-unique. The resolution of this debate lies in the interpretation of the record of continental freeboard17–19 and in the plausibility of large scale crustal recycling through the mantle via sediment subduction. We point out here that although the record of continental freeboard is consistent with either limited growth or no-growth models, recent sedimentation rates appear insufficient to support no-growth models. Note that evidence against a no-growth model is not necessarily evidence against minor sediment subduction.