Perspectives from global modeling of terrestrial Pb and Nd isotopes on the history of the continental crust

Transport balance modeling has been carried out to reconstruct present day Pb and Nd isotope data of the main accessible terrestrial reservoirs (upper mantle and continental crust). Models start from solar system initial ratios given by meteorite data and assume a start of Earth accretion at 4.55 Ga.The growth of the commentai crust, as well as its partial recycling into the mantle, through geological time are sensitive parameter sets, which can thereore be constrained. The-best in solution shows the crust to grow from zero at 4.4 Ga to 75% of its present mass by 1.6 Ga, with slower net growth thereafter. A marked increase in the rate of crust-mantle recycling, from c 10% of the crust production rate to c 50%, is indicated to have occurred between 2 and 1.5 Ga. It is speculated that this results from increased erosion after sufficient atmospheric oxygen made an ozone layer, and therefore land life, possible.