ABSTRACT

The establishment of an oxygenated atmosphere 2.4 billion years ago was heralded by a progression of environmental changes over the next 400 million years that permanently transformed global biogeochemical cycling. Newly obtained drillcore from Fennoscandia provides an unparalleled opportunity to establish a more continuous chronology of events through this interval. A team of investigators with expertise in isotopic and geochemical analysis and numerical modeling will produce a suite of environmental proxies of oceanic and atmospheric composition through the cored interval and interpret them quantitatively through numerical modeling in the context of a set of hypotheses concerning the pace of atmospheric oxygenation and the establishment of a strongly redox-stratified global ocean.

The intellectual merit of this proposal centers on the importance of reconstructing the sequence of global environmental change during this critical interval of Earth history. Widespread, perhaps even equatorial glaciation occurred as the deposition of banded iron formations, so characteristic of the Archean, ceased. A protracted interval of 13C enrichment in marine carbonates ensued, the first of its kind and the largest and longest in Earth history, without the expected evidence for abundant organic matter deposition.
Paradoxically, as carbon isotopic compositions returned to normal, tremendous quantities of organic matter and marine phosphorites were deposited. Various proxies indicate that oxidative weathering only became important toward the end of this interval of progressive biospheric change. Drill core from South Africa, complemented by field studies there and in Canada, the United States, Western Australia and Fennoscandia, have documented these events but the records are incomplete. Fennoscandian drillcore presents the best opportunity yet to fill these gaps, address the perplexing paradoxes of this time interval, and, with the establishment of a precise chronology based on Re-Os, assess the tempo of redox evolution of the atmosphere and ocean.

While there is general public interest in and curiosity about the subsurface, most people have little appreciation for the complexity of subsurface geologic structures and have no idea how geologists use the subsurface as an archive of the history of Earth. To improve this situation while addressing the broader impacts goals of the project, the investigators, together with their students, and museum and professional outreach staff will construct an interactive museum exhibit. The visitor will be able to extract lengths of rock core from a complex geologic structure displayed in three dimensions, and from these cores, reconstruct the geologic history of the area. Understanding will be aided by 3-D displays on the Penn State GeoWall, together with synthetic seismographs generated by the visitor at the push of a button. Additional broader impacts of this project include strengthening industry interests in the area of Re-Os systematics of organic-rich sedimentary rocks, and the involvement of a team of students and researchers in a truly international, interdisciplinary, multi-investigator project. Undergraduate research assistants will be drawn from diverse pools of applicants to our institutions? minority outreach program, e.g., the Big Ten Conference?s Summer Research Opportunities Program.

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