Anatoliy B. Kudryavtsev

Laser-Raman imagery of Earth's earliest fossils

Unlike the familiar Phanerozoic history of life, evolution during the earlier and much longer Precambrian segment of geological time centred on prokaryotic microbes. Because such microorganisms are minute, are preserved incompletely in geological materials, and have simple morphologies that can be mimicked by nonbiological mineral microstructures, discriminating between true microbial fossils and microscopic pseudofossil ‘lookalikes’ can be difficult. Thus, valid identification of fossil microbes, which is essential to understanding the prokaryote-dominated, Precambrian 85% of lifes history, can require more than traditional palaeontology that is focused on morphology. By combining optically discernible morphology with analyses of chemical composition, laser–Raman spectroscopic imagery of individual microscopic fossils provides a means by which to address this need. Here we apply this technique to exceptionally ancient fossil microbe-like objects, including the oldest such specimens reported from the geological record, and show that the results obtained substantiate the biological origin of the earliest cellular fossils known.

Raman and ion microscopic imagery of graphitic inclusions in apatite from older than 3830 Ma Akilia supracrustal rocks, west Greenland

Three-dimensional molecular-structural images of apatite grains and associated minerals embedded in a banded quartz-pyroxene-magnetite supracrustal rock from Akilia, southern west Greenland, were constructed by using Raman confocal spectroscopy. The rock sample is the same as that from which apatite-hosted isotopically light graphitic inclusions were reported by Mojzsis and colleagues in 1996; the results were challenged in 2005 by Lepland and colleagues who failed to find carbon-bearing inclusions in this and other Akilia samples. Here we demonstrate that inclusions of graphite wholly contained within apatite occur in this rock. The carbon isotopic composition of one such inclusion, its graphitic composition established by Raman spectroscopy, was measured by secondary ion mass spectrometry to be isotopically light (δ 13 C = –29‰ ± 4‰), in agreement with earlier analyses. Our results are thus consistent with the hypothesis that graphite-containing apatite grains of the older than 3830 Ma Akilia metasediments may represent chemical fossils of early life.

Raman spectra of a Lower Cambrian ctenophore embryo from southwestern Shaanxi, China

The Early Cambrian (≈540 million years old) Meishucun fossil assemblage of Ningqiang County (Shaanxi Province), China, contains the oldest complex skeletonized organisms known in the geological record. We here report the finding in this assemblage of an exquisitely preserved late-stage embryo of a ctenophore (“comb jelly”), its fine structure documented by confocal laser scanning microscopy and shown by Raman spectroscopy to be composed of carbonaceous kerogen permineralized in apatite. In its spheroidal morphology, the presence of eight comb rows and the absence of tentacles, this embryo resembles an adult ctenophore (Maotianoascus octonarius) known from the immediately younger Chengjiang fauna of Yunnan, China. The oldest ctenophore and the only embryonic comb jelly known from the fossil record, this exceptionally well preserved specimen provides important clues about the early evolution of the phylum Ctenophora and of metazoans in general.

Phosphate biomineralization in mid-Neoproterozoic protists

The origin and expansion of biomineralization in eukaryotes played a critical role in Earth history, linking biological and geochemical processes. However, the onset of this phenomenon is poorly constrained due to a limited early fossil record of biomineralization. Although macroscopic evidence for biomineralization is not known until the late Ediacaran, we here report biologically controlled phosphatic biomineralization of scale microfossils from mid-Neoproterozoic (pre-Sturtian) strata of northwest Canada. Primary biological control on mineralization is supported by the identification of apatite in both chert-hosted and limestone-hosted specimens, the conspicuously rigid original morphology of the scale microfossils relative to co-occurring organic-walled cyanobacteria and acritarchs, and the microstructure of the constituent phosphate. Cell-enveloping mineralized scales occur in a wide range of extant protists, but the apparent restriction of phosphate scales to one modern taxon of green algae suggests a possible affiliation for these fossils. Documentation of primary phosphate biomineralization in Fifteenmile Group (Yukon Territory, Canada) microfossils greatly extends the known record of biologically controlled mineralization and provides a unique window into the diversity of early eukaryotes.

Atomic force microscopy of Precambrian microscopic fossils

Atomic force microscopy (AFM) is a technique used routinely in material science to image substances at a submicron (including nm) scale. We apply this technique to analysis of the fine structure of organic-walled Precambrian fossils, microscopic sphaeromorph acritarchs (cysts of planktonic unicellular protists) permineralized in ≈650-million-year-old cherts of the Chichkan Formation of southern Kazakhstan. AFM images, backed by laser-Raman spectroscopic analysis of individual specimens, demonstrate that the walls of these petrified fossils are composed of stacked arrays of ≈200-nm-sized angular platelets of polycyclic aromatic kerogen. Together, AFM and laser-Raman spectroscopy provide means by which to elucidate the submicron-scale structure of individual microscopic fossils, investigate the geochemical maturation of ancient organic matter, and, potentially, distinguish true fossils from pseudofossils and probe the mechanisms of fossil preservation by silica permineralization.

Discovery of a New Chert-Permineralized Microbiota in the Proterozoic Buxa Formation of the Ranjit Window, Sikkim, Northeast India, and Its Astrobiological Implications

For the foreseeable future, the search for evidence of past life in rocks acquired from other planets will be constrained by the amount of sample available and by the fidelity of preservation of any fossils present. What amount of rock is needed to establish the existence of past life? To address this question, we studied a minute amount of rock collected from cherty dolomites of the Proterozoic Buxa Formation in the metamorphically altered tectonically active northeastern Himalaya. In particular, we investigated 2 small petrographic thin sections-one from each of 2 bedded chert horizons exposed in the Ranjit River stratigraphic section northwest of Rishi, Sikkim, India-that together comprise an area of approximately 5 cm(2) (about the size of a US postage stamp) and have a total rock weight of approximately 0.1 g. Optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy and imagery demonstrate that each of the thin sections contains a rich assemblage of 3-dimensionally permineralized organic-walled microfossils. This study, the first report of Proterozoic microfossils in units of the Ranjit tectonic window, demonstrates that firm evidence of early life can be adduced from even a minuscule amount of fossil-bearing ancient rock.

Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek Formation provide promising evidence of evolution's null hypothesis

Significance An ancient deep-sea mud-inhabiting 1,800-million-year-old sulfur-cycling microbial community from Western Australia is essentially identical both to a fossil community 500 million years older and to modern microbial biotas discovered off the coast of South America in 2007. The fossils are interpreted to document the impact of the mid-Precambrian increase of atmospheric oxygen, a world-changing event that altered the history of life. Although the apparent 2-billion-year-long stasis of such sulfur-cycling ecosystems is consistent with the null hypothesis required of Darwinian evolution—if there is no change in the physical-biological environment of a well-adapted ecosystem, its biotic components should similarly remain unchanged—additional evidence will be needed to establish this aspect of evolutionary theory. The recent discovery of a deep-water sulfur-cycling microbial biota in the ∼2.3-Ga Western Australian Turee Creek Group opened a new window to lifes early history. We now report a second such subseafloor-inhabiting community from the Western Australian ∼1.8-Ga Duck Creek Formation. Permineralized in cherts formed during and soon after the 2.4- to 2.2-Ga “Great Oxidation Event,” these two biotas may evidence an opportunistic response to the mid-Precambrian increase of environmental oxygen that resulted in increased production of metabolically useable sulfate and nitrate. The marked similarity of microbial morphology, habitat, and organization of these fossil communities to their modern counterparts documents exceptionally slow (hypobradytelic) change that, if paralleled by their molecular biology, would evidence extreme evolutionary stasis.

Confocal Laser Scanning Microscopy and Raman Imagery of the Late Neoproterozoic Chichkan Microbiota of South Kazakhstan

Abstract Precambrian microbiotas, such as that permineralized in bedded and stromatolitic cherts of the late Neoproterozoic, 750- to 800-Ma-old, Chichkan Formation of South Kazakhstan, have traditionally been studied by optical microscopy only. Such studies, however, are incapable of documenting accurately either the three-dimensional morphology of such fossils or their chemical composition and that of their embedding minerals. As shown here by analyses of fossils of the Chichkan Lagerstätte, the solution to these long-standing problems is provided by two techniques recently introduced to paleontology: confocal laser scanning microscopy (CLSM) and Raman imagery. The two techniques are used together to characterize, in situ and at micron-scale resolution, the cellular and organismal morphology of the thin section-embedded organic-walled Chichkan fossils. In addition, Raman imagery is used to analyze the molecular-structural composition of the carbonaceous fossils and of their embedding mineral matrix, identify the composition of intracellular inclusions, and quantitatively assess the geochemical maturity of the Chichkan organic matter. CLSM and Raman imagery are both broadly applicable to the study of fossils, whether megascopic or microscopic and regardless of mode of preservation, and both are non-intrusive and non-destructive, factors that permit their use for analyses of archived specimens. They are especially useful for the study of microscopic fossils, as is demonstrated in this first in-depth study of diverse taxa of a single Precambrian microbiota for which they provide information in three dimensions at high spatial resolution about their organismal morphology, cellular anatomy, kerogenous composition, mode of preservation, and taphonomy and fidelity of preservation.

Real time evolution of concentration distribution around tetragonal lysozyme crystal: case study in gel and free solution

Two-beam Michaelson interferometry was used to study concentration gradient layers around gel-grown tetragonal lysozyme crystals. Crystals were grown in gel to depress convection and mimic microgravity. The evolution of the concentration profile near the growing surface, the width of the concentration layer, surface concentration, and concentration gradient were investigated and the correlation of these parameters with lysozyme crystal growth is discussed. The concentration gradient properties of gel-grown crystals were compared to those obtained for solution-grown crystals and were found to be different from their solution-grown counterparts. In particular, concentration gradients were wider and transport rate were slower for gel-grown crystals than for solution counterparts.

Gypsum-Permineralized Microfossils and Their Relevance to the Search for Life on Mars

Orbital and in situ analyses establish that aerially extensive deposits of evaporitic sulfates, including gypsum, are present on the surface of Mars. Although comparable gypsiferous sediments on Earth have been largely ignored by paleontologists, we here report the finding of diverse fossil microscopic organisms permineralized in bottom-nucleated gypsums of seven deposits: two from the Permian (∼260 Ma) of New Mexico, USA; one from the Miocene (∼6 Ma) of Italy; and four from Recent lacustrine and saltern deposits of Australia, Mexico, and Peru. In addition to presenting the first report of the widespread occurrence of microscopic fossils in bottom-nucleated primary gypsum, we show the striking morphological similarity of the majority of the benthic filamentous fossils of these units to the microorganisms of a modern sulfuretum biocoenose. Based on such similarity, in morphology as well as habitat, these findings suggest that anaerobic sulfur-metabolizing microbial assemblages have changed relatively little over hundreds of millions of years. Their discovery as fossilized components of the seven gypsiferous units reported suggests that primary bottom-nucleated gypsum represents a promising target in the search for evidence of past life on Mars. Key Words: Confocal laser scanning microscopy-Gypsum fossils-Mars sample return missions-Raman spectroscopy-Sample Analysis at Mars (SAM) instrument-Sulfuretum.