Richard B. Hoover

Volcanic Glasses as Habitat for Microfossils: Evidence from the Early Paleoproterozoic Pillow Lavas of Karelia and their Modern Analogues in the Mid-Atlantic Ridge

Microbial complexes were identified in the volcanic glasses from the ancient (2.4-Ga-old basaltic pillowlavas of Karelia) and modern (pillow lavas of Mid-Atlantic ridge) volcanic rocks. It was shown that that their microbial colonization is likely to occur by the same mechanism. Thus, well preserved pillow lavas, which occupy a spacious fields in the Archean and Early Paleoproterozoic greenstone belts, are promising object for search of the earliest traces of life on Earth.

Development of living organisms on the lava-water interface of Palaeoproterozoic Ongeluk lavas of South Africa

An investigation of the Early Proterozoic pillow lavas of South-Africa shows that the lava-water boundary is very interesting from the point of view of bacterial paleontology. In the pillow selvages corresponding to this boundary, forms such as bacteria (including cyanobacteria) developed. Cyanobacterial or bacterial mats formed and probably even such highly organized forms as eukaryotes existed.

Phosphate biomineralization of cambrian microorganisms

As part of a long term study of biological markers, we are documenting a variety of features which reflect the previous presence of living organisms. As we study meteorites and samples returned form Mars, our main clue to recognizing possible microbial material may be the presence of biomarkers rather than the organisms themselves. One class of biomarkers consists of biominerals which have either been precipitated directly by microorganisms, or whose precipitation has been influenced by the organisms. Such microbe-mediated mineral formation may include important clues to the size, shape, and environment of the microorganisms. The process of fossilization or mineralization can cause major changes in morphologies and textures of the original organisms. The study of fossilized terrestrial organisms can help provide insight into the interpretation of mineral biomarkers. The study of fossilized terrestrial organisms can help provide insight into the interpretation of mineral biomarkers. This paper describes the results of investigations of microfossils in Cambrian phosphate-rich rocks that were found in Khubsugul, Northern Mongolia.

Possible biological structures in the Tissint Mars Meteorite

Preliminary SEM/EDAX studies of the Tissint meteorite shows projections of interior spherical globules rich in C and O. Such concentrations of carbonaceous material in a matrix of mineral grains pose a mystery. These structures are consistent with remnants of biological structures.

Bacterial paleontology for astrobiology

We review the development of Bacterial Paleontology and consider its relevance of the rapidly emerging field of Astrobiology. We present electron microscopic images of fossil bacteria in different states of preservation in Earth rocks and Astromaterials.

Evidence of ancient microbial activity on Mars

We report for the first time in situ observations of a relatively rare secondary iron arsenate-sulphate mineral named bukovskýite – Fe3+ 2(As5+O4)(S6+O4)(OH)•7(H2O) - found in a shock melt vein of the Tissint Martian meteorite. It is hypothesised that the mineral formed when high concentrations of aqueous H+, Fe(III), SO4 and AsO4 were maintained for long periods of time in microenvironments created within wet subsurface Martian clays. The aqueous H+, Fe(III), SO4 and AsO4 species arose from the microbial oxidation of FeS2 with concurrent release of sequestrated As. The availability of aqueous AsO4 would also be complemented by dissolution by-products of the microbial reduction of Feoxides influenced by dissolved organic matter that alters the redox state and the complexation of As, thus shifting As partitioning in favour of the solute phase. This hypothesis is substantially supported by SEM analysis of a 15μm spherical structure comprising of a carbonaceous outer coating with a inner core of FeS2 (pyrite) that showed the pyrite surface with spherical pits, and chains of pits, with morphologies distinct from abiotic alteration features. The pits and channels have a clustered, geometric distribution, typical of microbial activity, and are closely comparable to biologically mediated microstructures created by Fe- and S-oxidising microbes in the laboratory. These microstructures are interpreted as trace fossils resulting from the attachment of bacteria to the pyrite surfaces.

Acritarchs in carbonaceous meteorites and terrestrial rocks

Acritarchs are a group of organic-walled, acid-resistant microfossils of uncertain or unknown origin. Some are thought to represent the cysts or resting stages of unicellular protists (possibly dinoflagellates), chrysophytes (green algae) or other planktonic eukaryotic algae. Acritarchs are found throughout the geologic column extending back as far at 3.2 Ga. The presence of large sphaeromorphs in the Archaean provides evidence that the eukaryotic lineage extends much farther back in time than previously thought possible. Acritarchs are abundant in the Paleoproterozoic shales (1.9-1.6 Ga) of the former Soviet Union and they have been extensively used for the investigation of Proterozoic and Paleozoic biostratigraphy and paleoenvironmental parameters. Scanning Electron Microscope studies have revealed the fossilized remains of organic-walled microfossils of unknown origin and exhibiting characteristics of acritarchs in a variety of carbonaceous meteorites. In many cases, these remains are black or brown in color and have Carbon/Oxygen ratios suggesting they have been diagenetically converted into kerogen. It is not feasible that the fossilized remains of organicwalled microfossils such as acritarchs represent biological contaminant that invaded and became embedded in the rock matrix of carbonaceous meteorites within the short time periods of their residence on Earth. Consequently, these groups of microfossils are considered to provide an additional line for the existence of indigenous extraterrestrial microbial remains in meteorites. This paper presents a brief review of acritarchs in terrestrial rocks and provides images of a number of similar morphotypes of uncertain origin found in freshly fractured samples of carbonaceous meteorites.

Fossil microorganisms and formation of Early Precambrian weathering crusts

Weathering crusts are the only reliable evidences of continental conditions existence, and often are the only source of information about exogenous processes and subsequently about conditions under which the development of biosphere occurred. Complex of diverse fossil microorganisms was discovered in result of electronic-microscope investigations. Chemical composition of discovered fossils is identical to that of the host rocks and is represented by Si, Al, Fe, Ca and Mg. Probably, microorganisms fixed in rocks played role of catalyst. Decomposition of minerals, comprising rocks, and their transformation into clayey (argillaceous) minerals, occurred most likely under influence of microorganisms. And may be unique weathering crusts of Early Precambrian were formed due to interaction between specific composition of microorganism assemblage and conditions of hypergene transformations. So it is possible to speak about colonization of land by microbes already at that time and about existence of single raw from weathering crusts (Primitive soils) to real soils.

Chemical biomarkers and microfossils in carbonaceous meteorites

Chemical, mineral and morphological biomarkers and microfossils are present in a wide variety of ancient rocks and meteorites. We discuss previous results and present images of microfossils of cyanobacteria, magnetotactic bacteria, and acritarchs detected in the Orgueil, Mighei, Nogoya, and Murchison carbonaceous meteorites.

Evidence for biomarkers and microfossils in ancient rocks and meteorites

We review prior studies of chemical and morphological biomarkers in ancient rocks and meteorites and present recently obtained ESEM images of microfossils and nanofossils in-situ in freshly fractured surfaces of Nogoya and pristine samples of Murchison as further evidence of indigenous microfossils in meteorites.