Recent studies suggested that major oxidation events during the Ediacaran Period (ca. 635 Ma to 542 Ma) triggered the first appearance and evolution of the Earth?s earliest animal life, but critical evaluation of the proposed linkages is limited by the lack of a detailed documentation on spatial and temporal redox changes of Ediacaran oceans and the responses of Ediacaran organisms to such redox changes. An integrated geological, geochemical, and paleobiological study of the Ediacaran Yangtze platform is aimed at improving our understanding of the interplay between ocean redox changes, geochemical anomalies, and early animal evolution in a rarely preserved, fossiliferous sedimentary archive. The proposed research is designed to test the following hypotheses: (1) the deep ocean was anoxic/euxinic until ca. 551 Ma; (2) episodic oxidation of a large oceanic dissolved organic carbon (DOC) reservoir led to the formation of geochemical anomalies including unusually negative carbon isotope excursions; and (3) the spatial and temporal distribution of Ediacaran organisms was coupled with ocean redox conditions. Objectives of the research are to determine: (1) carbonate and organic carbon isotope variability across the basin to test a potential surface-to-deep ocean carbon isotope gradient that may have been much greater than in the modern ocean; (2) spatial and temporal sulfur isotope variability to test the persistence and/or fluctuation of sulfate reduction and sulfur disproportionation across the basin; (3) spatial and temporal changes of molybdenum (Mo) concentrations and Mo isotopes, iron (Fe) speciation and Fe isotopes to determine the secular redox evolution and potential redox fluctuation associated with stable isotope excursions; and (4) spatial and temporal occurrences of Ediacaran fossils and their relationships with geochemical boundaries/anomalies. The ultimate goal of the research is to integrate paleontological and geochemical data to test the coupling between redox conditions and spatial/temporal patterns of Ediacaran organisms. Anticipated data would provide important information for our understanding of the environmental forces related to a significant biological innovation in Earth history. The project will partially support four PhD students from University of Nevada Las Vegas, Virginia Polytechnic Institute, University of California at Riverside, and Arizona State University. The project develops new collaborations between researchers at four different institutions and provides a broad training opportunity for interactions among students with different research foci. Research results will be integrated with courses taught at four institutions and will enhance undergraduate involvement in the research project at four institutions. The project will also promote international collaborations with scientists from institutions in China and Canada.
The first animals on Earth and their early evolution, including the earliest steps in diversification of animal type and size and the beginnings of complex ecologies, happened between about 650 and 550 million years ago. This seminal moment in the history of life on Earth is almost universally attributed to a dramatic rise in the oxygen content of the ocean and atmosphere from earlier low levels that challenged the rise of complex life against a backdrop of bacteria and other single-celled microbes. Animals have comparatively high metabolic oxygen demands, and so the connection between the appearance of animals and rising oxygen is likely. Nevertheless, other possibilities exist, and independent, direct evidence for that O2 rise has been missing, particularly its precise timing and magnitude. Because convincing evidence has remained elusive and at times contradictory, circular arguments have emerged in recent years—pointing to animals as both the consequence of and evidence for early ocean oxygenation. This uncertainty stems largely from a lack of adequate chemical data that can trace widespread oxygenation in the ancient ocean. Specifically, we have been missing geochemical tracers that speak clearly to global ocean conditions before, during, and after the rise of animals. Fortunately, our study of trace metal abundances in the rocks of China goes a long way in filling this gap. These data from roughly 630-million-year-old organic-rich shales provide the earliest examples of metal enrichments similar to those seen in marine sediments today and thus convincingly fingerprint pervasive ventilation of the deep ocean, likely for the first time in Earth history and coincident with the earliest animal fossils. This early onset of ocean oxygenation jibes with independent estimates of high marine nutrient levels and inferred high levels of oxygen-producing life in the surface ocean following the greatest episode of glaciation in Earth history—the so-called ‘snowball Earth.’ Implicit in this convergence of events is the first compelling connection between the loss of global-scale ice cover on land, increasing diversity of life in the ocean, and rising oxygen contents of those waters. And it is this turn of events that set the stage for human origins following more than a half a billion years of animal evolution beneath an oxygen-rich atmosphere. The broader impacts of the project include training of two doctoral students and active participation by two postdoctoral fellows. These educational successes, including high-profile publication, are a tremendously positive outcome that has set the stage for the next steps in their research careers. Several undergraduate students from among the diverse student body at UC-Riverside assisted in the lab. This is an important opportunity that will steer their future career options. Lyons brought the findings of this project into his graduate class devoted to early Earth geobiology and wrote a exhaustive related book chapter now published to use as a teaching aid. Consistent with his desire to strengthen the geochemical community’s relationship with Precambrian biogeochemistry and the origins of life, he has co-organized symposia at three international conferences, and he has given many related lectures at conferences, workshops, summer courses, and universities in the U.S. and abroad. He has spoken on the subject to the general public. Finally, he has been an advocate for the importance of early biogeochemistry at multiple workshops and while serving on high-profile national committees. In all this outreach, Lyons has worked determinedly to educate wide ranging groups on the origins and evolution of early life and their relationships with the co-evolution of Earth’s ocean and atmosphere. He and his group are answering the essential questions of where humankind came from and where we are heading in the face of climate change, other human impacts, and concomitantly rapid loss of our glaciers and declining oxygen contents in the ocean.
