2012 Annual Science Report
University of Wisconsin Reporting | SEP 2011 – AUG 2012
Project 1D: Establishing Biogenicity and Environmental Setting of Precambrian Kerogen and Microfossils
This study demonstrates new abilities to use in situ measurements of carbon isotope ratios in microfossil kerogen as a biosignature and to establish taxonomic and micro-structural correlations.
Prior to the appearance of multicellular, shelled animals at the beginning of the Phanerozoic Eon, the fossil record is composed of unicellular or colonial microbes – rarely preserved, difficult to recognize, commonly morphologically ambiguous, and thus difficult to classify. In the Archean Eon, interpreting the fossil record is even more challenging due to the relatively poor preservation of “possible microfossils” that leads to debates about the biological origin of microbe-like organic structures. We chose four exceptionally preserved Precambrian microfossil communities in order to test whether we could measure the carbon isotopic composition of individual microfossils (and their microanatomical substructures) in situ, and with sufficient precision and accuracy to reveal any taxonomic or microstructural correlations that would provide information about microbial metabolism and be powerful indicators of biogenicity in older, possible microfossils. Using a combination of light and electron microscopy to support SIMS δ13C analysis, we demonstrated for the first time that such taxonomic and microstructural correlations in the carbon isotopic composition of Precambrian microfossils are preserved, and can be detected. One of the highlights of this study was our ability to distinguish, on the basis of their δ13C compositions, a colonial cyanobacterium and a eukaryotic alga preserved less than one centimeter apart in the same sample of ~750 million year old chert.
PROJECT INVESTIGATORS:John Valley
PROJECT MEMBERS:Takayuki Ushikubo
Martin Van Kranendonk
RELATED OBJECTIVES:Objective 2.1
Earth's early biosphere.
Environment-dependent, molecular evolution in microorganisms
Co-evolution of microbial communities
Effects of environmental changes on microbial ecosystems
Biosignatures to be sought in Solar System materials