nai

Project Progress

Eigenbrode has been developing thermochemolysis methodologies for extracting components of complex organics molecules from samples that pose unique analytical challenges because of their mineral composition. These include iron-oxide rich samples regarded as analogs to ancient aqueous environments on Mars and ancient Earth, as well as perchlorate-laden samples. The challenge in these cases is that the mineral oxidants can both chelate or ionically bond with the organics making them difficult to extract by traditional methods and contribute to partial or complete destruction of organic molecules over time (as in the rock record) or during traditional thermal extraction (in the lab).

Eigenbrode tested three traditional extraction techniques of samples from neutral-pH groundwater iron seeps, iron concretions from Lake Tyrrell, Australia (provided by Eric Roden, Univ. Wisconsin, and Dave Emerson, Bigelow Oceanographic Institute), and iron-oxidizing bacterial cultures from Dave Emerson (funded by an EPSCoR grant with Eigenbrode as a collaborator). In all cases, the expected biomolecular signatures were absent, though PAHs and some plant biomarkers were detected in the natural samples. This confirms that negative results of other studies may be misleading with regards to the organic biogeochemical status of the samples. Two to three new approaches are now being investigated that involve acidic pretreatment, thermochemolysis, and a combination of the two.

To understand the impact of perchlorate on analyses of sedimentary organic matter, Eigenbrode has added 1-5% perchlorate to a variety of sedimentary samples with features roughly analogous to sediments expected on Mars. Pyrolysis-mass spectrometry (also called evolved gas analysis; EGA), pyrolysis- gas chromatography mass spectrometry (GCMS), and thermochemolysis-GCMS methods are being used for initial bulk studies and will be followed up with solvent extraction approaches to ascertain the thermal impact on degradation during analysis. Figure 1 shows an example of altered organic chemistry by perchlorate addition to an Archean stromatolite sample known to contain both extractable hydrocarbons and kerogen. EGA and pyrolysis-GCMS results indicate so far that perchlorate influences the organic matter only in some circumstances. It is not yet clear what factors dictate when alteration occurs and by what mechanism. This investigation is ongoing. A manuscript containing current results on the impact of perchlorates and the applicability of the thermochemolysis approach for sediments of extreme chemistry is in preparation. In addition, this study has contributed to new perspectives on the organic (bio)geochemistry expected on Mars-a perspective being written up for a News and Views type article for submission to Astrobiology.

Carbon Isotopic Records of the Neoarchean
In collaboration with colleagues of the NAI MIT (Roger Summons et al.) and Wisconsin (John Valley, Ken Williford, et al.) teams, Eigenbrode is working to understand the spatial and molecular variations in stable carbon isotopes of sedimentary organic matter in the 2.7 to 2.5 Ga sedimentary record of Neoarchean Hamersley Province. This work was stimulated by the Rasmussen et al. Science paper and notable lack of analytical standardization, sample set integrity, and no consideration for alternative (biogeochemical) interpretations. The goal for this project is to assess how microbial inputs having a very broad isotopic range are preserved in the Archean record and if other non-biological components are recognizable. Most of our early work was steered towards developing a set of standards appropriate for Archean kerogens necessary for verifying results from the CAMECA 1280 Ion Microprobe. Preliminary results from three kerogen samples indicate a complex history of isotopic fractionation and organic partitioning. These results will be presented at AGU by Ken Williford et al.

Solid-phase sorbtive extraction of organic molecules in glacial ice
Eigenbrode has been studying organic molecular Signatures of Life in Ice (SLIce), which was supported by ROSES Exobiology and Mars Fundamental Research programs, and leverages from ASTEP (AMASE, led by PI Andrew Steele, CIW). Results of this work indicate that even in the most ideal circumstance of an ubitquitous biosphere, most detection methods for organic molecules in ice are not sensitive enough for robust scientific investigations to icy worlds. Ice essentially dilutes the astrobiological signatures we seek. To overcome this challenge, organic molecules need to be concentrated before analysis. A separate project funded by GSFC Internal Research and Development and led by Eigenbrode seeks to develop solid phase sorbtive extraction (SPSE) media for this purpose. Leveraging from the above studies and with support from NAI GCA, Eigenbrode teamed up with Gerstel, Inc. to test a realistic science application of SPSE (in the form of Gerstel Twisters) using meltwater from glacial ice samples collected in Svalbard. After exposing the SPSE material to 20 ml of sample for 2 hours, organic analytes were thermally desorbed and analyzed by gas chromatography mass spectrometry. The data indicates the presence of diverse compounds (Figure 2) including free fatty acids, PAHs, and some other hydrocarbons at 10-100 ppt concentrations, however, high background made it difficult to quantify and identify specific structures. In one case, the background signatures suggested the presence of tobacco (alkaloids and pyrazines), most likely originating from the breath of one of the field scientists that smoked cigarettes earlier in the day. These results provide support for further development of this approach for astrobiological studies on aqueous systems but also highlight the need for stringent organic molecular background control and monitoring. Future SLIce studies will integrate the SPSE approach.

Amino acid composition of glacial ice (substudy of the SLIce project that leverages support from NAI GCA)
As part of the SLIce study funded by EXOB and MFR programs, a subset of the filtered particulates of glacial-ice meltwater and associated environmental samples in the glacial environments of Svalbard were analyzed by Dworkin and Callahan for amino acid compositions. These data were collected and molecular interpretations are in progress by Eigenbrode and Floyd. The amino acid results are being merged with other molecular results (fatty acids, PAHs, other hydrocarbons, bacterial and eukaryotic biomarkers, bulk lipopolysacchride, bulk in situ adenosine triphosphate, and dissolved molecules) and contextual data for the same samples. This comprehensive molecular biosignature study is the heart of the SLIce investigations and is aimed at distinguishing different organic inputs to ice. SLIce will provide mission guidance for organic studies of extraterrestrial ices.