2009 Annual Science Report

Arizona State University Reporting  |  JUL 2008 – AUG 2009

Stoichiometry of Life, Task 3a: Ancient Records - Geologic

Project Summary

The primary goal of this effort is to understand the evolving redox state of the atmosphere and ocean at critical intervals in Earth history, its effect on the availability of bioessential elements, and the consequences for evolution. In support of this goal, a major effort is underway to analyze, at high resolution, ~2.5- to 1.5-billion-year-old drill core samples so that we can better understand the distribution and evolution of early eukaryotic organisms at a variety of spatial and temporal scales. Additional efforts focus on characterizing life and environment leading in to the Cambrian explosion of metazoan life.

4 Institutions
3 Teams
19 Publications
2 Field Sites
Field Sites

Project Progress

Most efforts over the past year have centered on (1) publication preparation and (2) collection and preliminary analysis of new samples keyed to questions of mid-Proterozoic biospheric evolution.

The publications are the culmination of an intense period of study of the latest Archean, just prior to the Great Oxidation Event (GOE) ~2.4 billion years ago. Our work is pointing to photosynthetic oxygen production before the GOE, with impacts on metal and sulfur inventories in the ocean and the spatiotemporal fabric of deep and shallow ocean chemistry, including evidence for oxic surface waters and the oldest records of euxinia at depth. These papers involved ASU Team PI Anbar, co-I Lyons (UC Riverside), students and postdocs at both institutions, and collaborator Roger Buick at U. Washington.

Sample acquisition is the critical first step as we begin our study of mid-Proterozoic ocean chemistry and associated organic biomarker trends. To this end, a group of five from UCR, including co-I Lyons and Ph.D. student Reinhard, traveled to north China during summer ‘09 to join colleagues from the Chinese Academy of Sciences. Together, they collected an outstanding suite of fresh outcrop samples just north of Beijing for organic and inorganic analysis. The emphasis of the organic work is patterns of prokaryotic diversity, including a search for photic euxinia and ecological relationships in light of independent, inorganic constraints on paleoredox. Preliminary work suggests episodes of ferruginous conditions in the deep ocean. Second, co-I Love will search, within a tight facies and geochemical framework defined by inorganic analyses, for molecular evidence for eukaryotes in strata roughly coeval with the oldest robust fossil records of these organisms. UCR Postdoc Chao Li, who is familiar with all aspects of this study, including past experience with these rocks, is now in place to undertake this work.

Part two of the mid-Proterozoic study centers on 1.64- and 1.5- to 1.4-billion-year-old rocks from north central Australia in the region of the McArthur Basin. New postdoc Amy Kelly (09 PhD, MIT) planned to joined Lyons for two weeks of drill core subsampling in Darwin (fall 09) to add to samples already in hand through collaboration with Roger Summons (PI of the MIT NAI Team). This additional collecting will emphasize three cores (Roper Group and Barney Creek Fm.), and several hundred outstanding additional samples are now in hand. Kelly will spend one year at UCR with Love and Lyons, followed by one year at ASU with Anbar — integrating diverse organic and inorganic techniques.

In additional efforts aimed at the Neoproterozoic and Precambrian-Cambrian boundary, ASU M.S. student Michael Sheehan together with collaborator Paul Knauth successfully developed an accurate mass spectrometric procedure for analyzing small samples of hydrous minerals for H isotopes. They plan to use this technique to study cherts already analyzed for oxygen isotopes to test for a major climatic temperature change at the Precambrian-Cambrian boundary. A remarkable warming event has been inferred from O isotopes alone, but the H isotope data are also needed to make a convincing case. In Year 1 collaborator Knauth also published a provocative paper reinterpreting Neoproterozoic C isotope data as providing evidence of an explosive “greening” of the continents, which may have helped trigger the Cambrian explosion of life.