Exobiology and Evolutionary Biology

Carbonaceous associations with apatite in Precambrian banded iron formations (2)

PI: Dominic Papineau

Banded iron formations (BIFs) are the main economic sources of iron on Earth, yet their origin is still not well understood. Recent experimental work suggests that microorganisms likely played a key role in the formation of these common Precambrian rocks, which is significant because the oldest terrestrial sedimentary rocks are BIFs. If microorganisms were indeed involved in BIF formation, a hypothesis is that there should exist organic and/or other remains of their past presence in BIFs. Our preliminary observations indicate that microscopic carbonaceous material is commonly associated with apatite grains in BIFs of various ages and metamorphic grades. The objectives of this proposed research project are to provide detailed petrographic information on carbonaceous associations with apatite in various BIFs and to characterize the structure and chemical and isotopic compositions of this carbon. Our hypothesis is that the association of carbonaceous material with apatite in BIFs can be used as a biosignature if all the following conditions are met:

- the carbon isotopic composition is consistent with a biological origin, – the presence of heteroatoms such as O, H, N, S, and/or P can be detected in carbonaceous material, and – these characteristics have to be consistent with metamorphic overprints when comparing low and high grade BIFs.
Several tests of this hypothesis will be performed to evaluate possible abiotic mechanisms of formation, including structural analyses to determine crystallographic orientation patterns that may be consistent with fluid-deposited graphite, and the presence of nano-phase metals in carbonaceous material that could have acted as catalysts for Fisher-Tropsch-type reactions. Another critical negative test will be performed with the same approach on apatite-carbonaceous associations from abiotic systems, such as in an occurrence found in a Martian meteorite of igneous origin. A focus of the proposed work will also be on graphite associated with apatite in the >3.83 billion years old quartz-pyroxene (Qp) rock from the Island of Akilia in southwest Greenland, which is of BIF affinity and is the oldest terrestrial sedimentary rock.
Observations and analyses by several micro-analytical techniques will provide a complete characterization of carbonaceous material associated with apatite and enable an assessment of the origin of carbon. We will use an arsenal of state-of-the-art micro-analytical methods to analyze the structure of carbonaceous material associated with apatite (by Laser Confocal Raman micro-Spectroscopy and Transmission Electron Microscopy) and its chemical and isotopic composition (with various electron beam techniques, synchrotron-based Scanning Transmission X-ray Microscopy, and Secondary Ion Mass Spectrometry). The anticipated data will provide constraints for the origin of carbonaceous material in BIFs, which may help to understand the origin of BIFs and biological evolution on the early Earth. The proposed research project is therefore highly relevant for several NASA programs including Exobiology and Evolutionary Biology, Mars Exploration, and the Astrobiology Institute.