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2003 Annual Science Report

University of California, Los Angeles Reporting  |  JUL 2002 – JUN 2003

Geobiology and Geochemistry of Early Earth

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

We continue to pursue fruitful cross-team collaborations in the fields of geobiology and geochemistry related to astrobiology. Many new data are being generated and are currently in the final stages of preparation for submittal.

The UCLA ion microprobe laboratory has continued to serve as a unique resource for obtaining data relevant to a number of research projects involving UCLA and other NAI lead teams. The measurement of mass-independent isotope fractionation (MIF) effects in sulfur from a variety of ancient materials was a primary focus for the last year. In one project, with Steve Mojzsis (U. Colorado), we found D33S anomalies ranging up to 2 permil in Archean sedimentary sulfides from Greenland and Western Australia. Our results provide unequivocal supporting evidence, obtained by a completely independent technique, for the existence of mass-independent sulfur isotope anomalies in Archean sulfides, as discovered by James Farquhar (University of Maryland) and collaborators. The data support the notion of an anoxic atmosphere on the Earth before ~ 2Ga. The presence of MIF sulfur in sulfides from a 3.8 Ga Fe-rich quartzite from Akilia Island is consistent with a marine sedimentary origin for this rock. This is significant since this same sample was shown to exhibit isotopically light carbon, suggestive of biogenic fractionation by Mojzsis and coworkers. In a second study, conducted with Farquhar and his postdoc B. Wing, we discovered MIF sulfur effects preserved in sulfide inclusions in diamonds from the Orapa Kimberlite pipe, Kaapvaal-Zimbabwe craton, Botswana. The data indicate that sulfur was transferred from the atmosphere to the source regions of diamonds and thus have implications for sulfur cycling in the Archean. We continue to work on various projects related to understanding sulfur cycling through Earth history, both UCLA-led and in collaboration with the U. Colorado and U. Maryland groups.

Additionally, we have participated in an international consortium, led by T. Mark Harrison, to investigate the Earth’s earliest surviving minerals. We have assisted Harrison in performing ion microprobe Pb-Pb analyses of > 10,000 detrital zircons from the Jack Hills, Western Australia. These reconnaissance studies succeeded in identifying individual zircons > 4.2Ga. These ancient samples are designated for a host of geochemical analyses that will address diverse questions from the origin of the atmosphere to the nature of Earth’s oldest known crustal materials.

A cross-team collaboration with Penn State was initiated in 2002-2003. In this study UCLA graduate student Tracey Herrera spent one month at Penn State in summer, 2002, conducting experiments on culturing Methanopyrus kandleri. The purpose of the work was to culture this organism during reaction of olivine to serpentine. We succeeded in identifying optimum conditions for Methanopyrus growth, as well as in determining the effects of organism growth on fluid composition. The work was presented at the NAI meeting at Arizona State University.

A new facility for measuring stable isotope ratios was nearly completed this past year at UCLA. the new laboratory will facilitate projects dealing with the origin of carbon isotope ratio excursions in limestones of marine origin that mark major shifts in ocean chemistry and correlate with mass extinctions. Our group will collect carbon isotope ratio data on sections of limestone from Siberia that mark one such global isotopic excursion during the Lower Cambrian. By providing enhanced time resolution in the C isotopic record that can be correlated with biostratigraphic zones, this work should help resolve questions surrounding the causes of these enigmatic times in Earth history that ultimately lead to an expansion in biological diversity.

Work was also completed on a new multi-collector inductively coupled plasma-source mass spectrometer (MC-ICPMS) laboratory at UCLA that will permit us to examine the interchange of metals (e.g., Fe) between the biological and inorganic chemical realms. The capabilities afforded by this new facility completed this year will be used to investigate the ecology of primitive organisms that existed on ancient Earth using the isotopes of Fe and Mg as indicators of the mutual dependence of the organisms and their geochemical surroundings.