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Don R. Baker et al, A metasomatic mechanism for the formation of Earth’s earliest evolved crust, Earth and Planetary Science Letters (2017). DOI: 10.1016/j.epsl.2017.01.022

More than 90% of Earth’s continental crust is made up of silica-rich minerals, eg, feldspar and quartz. But where did this silica-enriched material come from? And could it provide a clue in the search for life on other planets? Conventional theory holds that all of the early Earth’s crustal ingredients were formed by volcanic activity. Now, McGill University earth scientists Don Baker and Kassandra Sofonio have published a theory with a twist: some chemical components of this material settled onto Earth’s early surface from the steamy atmosphere that prevailed at the time.

First, a bit of ancient geochemical history: Sc...