There were no large volumes of felsic continental crust in the early Earth

New model growth curves for the continental crust based upon Hf-isotopes in zircon suggest that large volumes of felsic continental crust were present in the Hadean and early Archaean. These models sit uncomfortably with estimates of the volume of ancient crust preserved today and imply that the large volumes of crust that were created early in Earth history are now lost. However, this paper argues that there is no evidence from modern mantle geochemistry that very large volumes of early continental crust have been recycled into the mantle. In contrast significant volumes of Archaean crust may have been reworked into younger crust, although there is no evidence that this process took place in the early Archaean and Hadean. Geological evidence from the detrital zircon record does not show evidence for large volumes of very early felsic crust, rather, geochemical proxies for Eo-Archaean and Hadean crust strongly suggest that the earliest crusts on Earth, some of which may have been subaerial, were mafic. A lack of very early felsic crust on Earth calls for a re-evaluation of current crustal growth curves and geodynamic models for the start of plate tectonics, the role of supercontinents in early continent formation and the role of the subcontinental lithosphere in continent preservation. The earliest felsic rocks on Earth may have taken the form of oceanic plagiogranites or ocean-island potassic granites as found in the modern.

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