The Origin and Expansion of Silica Biomineralization and Its Influence on the Global Silica Cycle

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Some marine organisms construct their skeletons from opaline silica. In modern oceans, this process—silica biomineralization—plays an important role in the regulation of Earth’s climate and major elemental cycles. Observations from the rock record offer conflicting views on how long ago the first silica biomineralizers evolved and whether they played as important a role in regulating the oceans as their modern relatives. This project will investigate these questions by measuring the stable isotope composition of silicon in the oldest fossils of sponges and radiolarians, focusing on samples from the western US ranging in age from 520-440 million years. This project will include research training for graduate, undergraduate, and high school students; science engagement experiences for 200 elementary school girls; and the development of a museum exhibit on the first silica biomineralizers. The evolution and expansion of silica biomineralization at the beginning of the Paleozoic Era initiated the transformation of the silica cycle from a system governed by strictly abiotic reactions to the biologically-dominated cycle that characterizes modern oceans. Our current understanding of this transition is limited by conflicting data on the timing of the evolution and expansion of the first silica biomineralizers and untested hypotheses about their influence on the silica cycle. This project will bridge this knowledge gap by address two primary research objectives: (1) document the preservational modes of fossil sponge spicules and radiolarians to evaluate their influence on preservation of primary Si isotope values; and (2) build an improved Cambrian-Ordovician record of Si isotope values in fossil sponge spicules and radiolarians. This work will include Si and O isotope ratio analyses of siliceous fossils in situ via secondary ion mass spectrometry, combined with additional microanalytical characterization via micro X-ray fluorescence, Raman microspectroscopy, and wavelength-dispersive X-ray spectroscopy, and a suite of models describing the marine silica cycle. These data will provide a novel approach to resolving long-standing questions surrounding the early Paleozoic biological transformation of the global silica cycle, including how the marine system responded to major perturbations in silicate weathering fluxes driven by climate and tectonics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.