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As the complexity and diversity of life on Earth keeps getting pushed further back in time with more and more data from the geologic record, the issue of the role of continents in the evolution of the early biosphere has become increasingly prominent. Are emergent continents required for life’s origin? Are nutrients such as P dependent on exposure of evolved continental crust? Are the ecological niches provided by extensive continental shelves required for a diverse ecosystem?

Scientists with the NASA Astrobiology Institute team based at the University of Wisconsin conducted a detailed study of Sr isotope compositions of Archean carbonates, which adds to an earlier study of Archean barite published in 2016, to provide a fairly complete view of the Sr isotope composition of Archean seawater.

The paper, “Initiation of modern-style plate tectonics recorded in Mesoarchean marine chemical sediments,” is published in Geochimica et Cosmochimica Acta.

Their results show that emergent and evolved (granitic) continental crust was extensive since at least 3.2 Ga. When considered along with geochemical, metamorphic, and thermal models for crustal evolution, this time period likely coincides with the initiation of modern-style plate tectonics, highlighting the intimate linkages that exist between plate tectonics, continental evolution, and the biosphere in the Archean Earth. Although it has been said that early life simply “enjoyed” continental crust and plate tectonics, the convergence of multiple lines of evidence suggests a more important role for solid-Earth processes in the evolution of the biosphere than previously thought.

The research was funded by the NASA Astrobiology Institute and the National Science Foundation, with support from the Natural Sciences and Engineering Research Council of Canada.

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