A Field Guide to Finding Fossils on Mars

The Martian surface is cold, dry, exposed to biologically harmful radiation and apparently barren today. Nevertheless, there is clear geological evidence for warmer, wetter intervals in the past that could have supported life at or near the surface. This evidence has motivated National Aeronautics and Space Administration and European Space Agency to prioritize the search for any remains or traces of organisms from early Mars in forthcoming missions. Informed by (1) stratigraphic, mineralogical and geochemical data collected by previous and current missions, (2) Earth's fossil record, and (3) experimental studies of organic decay and preservation, we here consider whether, how, and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early Mars. We conclude that Noachian-Hesperian Fe-bearing clay-rich fluvio-lacustrine siliciclastic deposits, especially where enriched in silica, currently represent the most promising and best understood astropaleontological targets. Siliceous sinters would also be an excellent target, but their presence on Mars awaits confirmation. More work is needed to improve our understanding of fossil preservation in the context of other environments specific to Mars, particularly within evaporative salts and pore/fracture-filling subsurface minerals.

Patterns of metal distribution in hypersaline microbialites during early diagenesis: Implications for the fossil record

The use of metals as biosignatures in the fossil stromatolite record requires understanding of the processes controlling the initial metal(loid) incorporation and diagenetic preservation in living microbialites. Here, we report the distribution of metals and the organic fraction within the lithifying microbialite of the hypersaline Big Pond Lake (Bahamas). Using synchrotron-based X-ray microfluorescence, confocal, and biphoton microscopies at different scales (cm-μm) in combination with traditional geochemical analyses, we show that the initial cation sorption at the surface of an active microbialite is governed by passive binding to the organic matrix, resulting in a homogeneous metal distribution. During early diagenesis, the metabolic activity in deeper microbialite layers slows down and the distribution of the metals becomes progressively heterogeneous, resulting from remobilization and concentration as metal(loid)-enriched sulfides, which are aligned with the lamination of the microbialite. In addition, we were able to identify globules containing significant Mn, Cu, Zn, and As enrichments potentially produced through microbial activity. The similarity of the metal(loid) distributions observed in the Big Pond microbialite to those observed in the Archean stromatolites of Tumbiana provides the foundation for a conceptual model of the evolution of the metal distribution through initial growth, early diagenesis, and fossilization of a microbialite, with a potential application to the fossil record.

Empowerment: a view of two low-income African-Americans communities

Field theory and empowerment were used as guiding conceptual frameworks to address empowerment issues in two low-income inner city African-Americans communities. Field theory and empowerment provided a conceptualization of these communities in terms of the possible impact of the physical environment of these communities on their residents and the health care professionals who worked with these residents. The most likely response is learned helplessness and depression that are antithetical to empowerment. These frameworks also were helpful in generating strategies to foster empowerment among these community residents. These strategies include helping residents to redefine their behavior as ways of coping with a hostile environment that confronts them with poverty and racism and to reconnect with natural supports in the community for the purpose of enhancing community coalitions and alliances.

Mutagenic activity and identification of excreted platinum in human and rat urine and rat plasma after administration of cisplatin

Cisplatin and its biotransformation products were analyzed in human and rat urine and in plasma from rats. Analyses were performed using high performance liquid chromatography (HPLC). Microbial mutagenesis assays were performed on effluents from the chromatographic system. After intravenous administration to man (50 mg/m2) and intravenous and intraperitoneal administration to rats (5-10 mg/kg), platinum was excreted in the urine in a form that co-eluted mainly with cisplatin. Unbound drug in the plasma co-eluted with cisplatin. Furthermore excreted platinum exhibited mutagenic and chemical reactivity similar to that of cisplatin. We conclude that the principal form of free platinum circulating in blood and excreted in urine is cisplatin.