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Science. 2017 Sep 22;357(6357):1271-1274. doi: 10.1126/science.aan8086.

Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago.

Author information

1
Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60615, USA. nicolas.greber@unige.ch.
2
Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60615, USA.
3
Department of Earth Sciences, University of California, Riverside, CA 92521, USA.
4
Department of Geology, University of Johannesburg, Post Office Box 524, Auckland Park, 2006, Republic of South Africa.
5
Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, USA.

Abstract

Earth exhibits a dichotomy in elevation and chemical composition between the continents and ocean floor. Reconstructing when this dichotomy arose is important for understanding when plate tectonics started and how the supply of nutrients to the oceans changed through time. We measured the titanium isotopic composition of shales to constrain the chemical composition of the continental crust exposed to weathering and found that shales of all ages have a uniform isotopic composition. This can only be explained if the emerged crust was predominantly felsic (silica-rich) since 3.5 billion years ago, requiring an early initiation of plate tectonics. We also observed a change in the abundance of biologically important nutrients phosphorus and nickel across the Archean-Proterozoic boundary, which might have helped trigger the rise in atmospheric oxygen.

PMID:
28935801
DOI:
10.1126/science.aan8086
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