The detection of biominerals, chemical biomarkers, and putative microfossils in the Mars meteorite, ALH84001, stimulated the newly emerging fields of astrobiology and bacterial paleontology. The debate triggered by the ALH84001 results highlighted the importance of developing methodologies for recognizing chemical biomarkers, biominerals, and microfossils in living and fossilized bacteria in ice, permafrost, rocks, meteorites, and other astromaterials prior to the return of samples from comets, asteroids, and Mars. Comparative studies of the chemical, mineral, and morphological biomarkers in living and fossil microorganisms are essential to developing the expertise needed to differentiate biogenic forms from abiotic microstructures and to recognize indigenous biosignatures and distinguish them from recent biological contaminants.
At the NASA Marshall Space Flight Center (MSFC) and the Paleontological Institute of the Russian Academy of Sciences (PIN/RAS), ultrahigh-resolution imaging and x-ray elemental analysis has been carried out on living bacteria, ancient microbes cryopreserved in ice and permafrost, biominerals and microfossils in a wide variety of rocks and meteorites. The environmental scanning electron microscope (ESEM) and field emission scanning electron microscope (FESEM) studies have resulted in the detection of a large number of indigenous biomarkers and lithified or carbonized microfossils found embedded in situ in the rock matrix of carbonaceous meteorites. Many of these forms are similar to microfossils and biominerals seen in living and fossil magnetotactic bacteria and cyanobacteria from hypersaline soda lakes; phosphorites of Khubsugul, Mongolia; and high carbon rocks of the Siberian and Russian Platforms. Some of the assemblages of microfossils in carbonaceous meteorites exhibit consistent consortia and microbial ecosystems. Many of the forms are large and extremely complex, exhibiting recognizable nanostructures, such as flagella, spines, biofilms, apical cells, and reproductive stages (trichomes, spores, akinetes, and hormogonia) such as are known in modern Nostocacean cyanobacteria. A review of the prior studies and recently obtained images, and x-ray data from a wide variety of carbonaceous meteorites and terrestrial rocks is provided herein.