2003 Annual Science Report
NASA Johnson Space Center Reporting | JUL 2002 – JUN 2003
We define mineral biosignatures to be those minerals that exhibit properties that are characteristic of, produced by, or influenced by biological activity. Furthermore, these properties must be such that they could not reasonably occur through random, stochastic interactions in the natural environment . One example is magnetite (Fe3O4), which is an abundant mineral on Earth and is typically formed through inorganic processes. When magnetite is formed intracellularly by prokaryotic organisms called magnetotactic bacteria, the crystals display a morphology, size distribution, and chemical purity that have never been observed in the absence of biogenic activity. These properties are controlled by the cell and are a product of evolution. Unlike organic biomarkers, which represent the molecular components of an organism, mineral biosignatures represent the interaction of an organism with its environment. Hence mineral biosignatures make no assumption as to the molecular makeup of the organism and so are inherently less Earth-centric. Analysis of the Martian meteorite Allan Hills 84001 (ALH84001) revealed several lines of evidence that have led some investigators to suggest that microbial life existed on Mars approximately four Ga (billion annum) ago. One of the strongest lines of evidence is the presence of tens-of-nanometer sized magnetite [Fe3O4] crystals found within carbonate globules and their associated rims in the meteorite.
We continue to confirm our original geometry for _ of the magnetite population in the ALH84001 carbonate globules to be of identical geometry to a magnetotactic bacteria strain known as MV-1 through transmission electron microscope tomography. This technique has confirmed the original geometry of MV-1 and ALH84001 magnetite to be indistinguishable.
We are continuing progress of producing chemically simplistic analogs to the ALH84001 carbonates. Experimental work by Chris Romanek and colleagues at the Savannah River Ecology Laboratory shows that both magnetite and siderite can be produced at relatively low temperatures from aqueous solutions under CO2 partial pressure equal to that on Mars. These carbonates have been heated to produce magnetite that can be compared with those observed in ALH84001.
We have also begun a research collaboration with Neva Ciftcioglu and her study of “nanobacteria” mineralization of a unique morphological calcium phosphate shells that grow around the nanoforms. The genetic makeup and the nature of the nanobacteria and associated mineralization process is still being categorized at present. Preliminary results indicate the presence of ribonucleic acid (RNA). Current collaboration with the MAYO Institute will conform these results within the year.
Working with Lisa Robbins and her graduate student Van Cleave, we have developed the foundation and protocols to test the hypothesis that ancient microbes can be utilized to produce suites of minerals similar to those found in ALH84001. Using the chemolithotrophic thermophile Archeaoglobus fulgidus, a variety of carbonate minerals were produced in laboratory experiments, including iron, magnesium and calcium carbonates. We propose to continue producing carbonates for examination of biomarkers within these microbially induced minerals. These mineral suites can be analyzed through a variety of methods, including scanning electron micrography (SEM), transmission electron microscopy (TEM), and fluorescent microscopy.
PROJECT INVESTIGATORS:Kathie Thomas-Keprta
PROJECT MEMBERS:Dennis Bazylinski
RELATED OBJECTIVES:Objective 2.1
Outer Solar System exploration
Biosignatures to be sought in Solar System materials