This award to the University of Wisconsin Madison will help us understand the early Earth and the chemical characteristics of Earth's early oceans. It is interdisciplinary, and could turn over old and ill-constrained paradigms. This proposal will address some very important questions from the Archaean, earlier than 2-1/2 billion years ago: when did plate tectonics begin, how quickly was continental crust built up, did it occur in episodes, how did this affect evolution of life, and how did the emerging continents and their on-board life affect ocean chemistry and the appearance and setting of banded iron formations? Sets of K-12 educational material developed by specialists will be disseminated through the NSF-funded Portal to the Public, and the research results will be used to design and develop illustrations of 'Archean Worlds,' which will be incorporated into tours of the Madison Geology Museum.
The work will provide fundamental constraints on the starting date for plate tectonics and the role of lateral tectonic processes. The enhanced understanding of Archean carbonates will bear directly upon the development of banded iron formations, the chief source of iron ore. This work will constrain Archaean topography and hypsometry (the Flat Earth/Water World scenarios). The proponents will refine the existing overly simplistic 87Sr/86Sr Archean seawater curve by looking at seven suites of extremely well characterized marine carbonates. This is a serious attempt at understanding the residence time of Sr in Archaean seawater, and how this may have changed due to changes in the mantle and continental sources. Any new seawater 87Sr/86Sr curve for the Archaean would have a truly transformative effect on our understanding of Archean geochemistry by helping to settle the controversy on whether iron formations and carbonates in the Archean were deposited in restricted basins vs. open ocean, as well as constraining Archaean subareal weathering fluxes of silicic continental material. The project will also use REE+Y systematics to deal with the origin and extent of hydrothermal input vs. continental weathering as well as the oxidation state of Archaean seawater, and perform work on the same samples with C, O, Mg, Fe, and Mo isotopes with funding from NASA.
This work is a NSF-NASA inter-agency collaboration on Early Earth.
