Evolution of the continental crust

The continental crust covers nearly a third of the Earth’s surface. It is buoyant—being less dense than the crust under the surrounding oceans—and is compositionally evolved, dominating the Earth’s budget for those elements that preferentially partition into silicate liquid during mantle melting. Models for the differentiation of the continental crust can provide insights into how and when it was formed, and can be used to show that the composition of the basaltic protolith to the continental crust is similar to that of the average lower crust. From the late Archaean to late Proterozoic eras (some 3–1 billion years ago), much of the continental crust appears to have been generated in pulses of relatively rapid growth. Reconciling the sedimentary and igneous records for crustal evolution indicates that it may take up to one billion years for new crust to dominate the sedimentary record. Combining models for the differentiation of the crust and the residence time of elements in the upper crust indicates that the average rate of crust formation is some 2–3 times higher than most previous estimates. Crusty role The Earth's continental crust has a key role in the evolution of the planet, yet when and how it formed remain the subject of much debate. Advances in analysis of isotopic content of newly generated continental crust have led to more robust models of crustal evolution in recent years. Chris Hawkesworth and Tony Kemp review these developments. Combining models for crust differentiation, and the residence time of elements in the upper crust, suggests that the average rates of crust formation were two or three times higher than most previous estimates.