life on mars evaluation of the evidence within martian meteorites alh84001 nakhla and shergotty abstract analyses both support and are in opposition to the hypothesis that the martian meteorite alh84001 contains evidence for possible biogenic activity on mars new observations in two additional martian meteorites nakhla 1 3 ga old and shergotty 300 165 ma old indicate possible biogenic features features in the three martian meteorites compare favorably with the accepted criteria for terrestrial microfossils and evidence for early life on the earth there is strong evidence for the presence of indigenous reduced carbon biogenic magnetite and the low temperature formation of carbonate globules the morphological similarities between terrestrial microfossils biofilms and the features found in the three martian meteorites are intriguing but have not been conclusively proven every investigation must recognize the possibility of terrestrial contamination of the meteorites whether or not the meteorites are martian the search for evidence of ancient life in martian meteorites has emphasized the difficulties confronting the scientific community with the respect to the positive identification of evidence of past biogenic activity

evidence for microbes in early neoproterozoic stromatolites abstract the biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin this has particularly been the case with older precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics in some cases however evidence has been preserved through very early mineralisation precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms this study provides evidence from early neoproterozoic columnar stromatolites in the jiuliqiao formation from the southeastern margin of the north china platform for fossilized extracellular polymeric substances eps and cyanobacteria along with nanospheres which may represent permineralised viruses or viral like particles a similar chemical composition and colour along with their embedded and cross cutting relationships with the matrix suggest they are syn depositional products and not modern artefacts or the result of sample preparation the interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping baffling and binding processes the presence of virus like particles and mineralized eps with anhedral fine grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation this study demonstrates the use of a high definition scanning electron microscope to detect fossilized calcified filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

nucleation and stabilization of eocene dolomite in evaporative lacustrine deposits from central tibetan plateau in past decades the formation of dolomite at low temperature has been widely studied in both natural systems and cultured experiments yet the mechanism s involved in the nucleation and precipitation of dolomite remains unresolved late eocene dolomitic deposits from core in the upper niubao formation lunpola basin central tibetan plateau china are selected as a case study to understand the dolomitization process es in the geological record dolomite formation in lunpola basin can be ascribed to a different mechanism forming the large quantities of replacive dolostones in the geological record and provides a potential fossil analogue for primary dolomite precipitation at low temperature this analogue consists of an alternation of laminated dolomitic beds organic rich and siliciclastic layers formed in response to intense evaporation interpreted to take place in a continental shallow lake environment mineralogical textural and stable isotopic evaluations suggest that the dolomite from those dense clotted laminated beds is a primary precipitate at the nanoscale these dolomitic beds are composed of ca mg carbonate globular nanocrystals diameter 80 to 100 nm embedded in an organic matrix and attached to clay flakes micro infrared spectroscopy analyses have revealed the presence of aliphatic compounds in the organic matrix microscopic and elemental compositional studies suggest that clay surfaces may facilitate the nucleation of dolomite at low temperature in the same way as the organic matrix does the dolomite laminae show values for 18ovpdb from 3 2 to 1 76 and for 13cvpdb from 2 62 to 3 78 inferred 18osmow values of the lake water reveal typical evaporitic hydrological conditions these findings provide a potential link to primary dolomite formation in ancient and modern sedimentary environments and shed new light on the palaeoenvironmental conditions in central tibet during the eocene

origin of highly elongate calcite cemented concretions in some italian coastal beach and dune sands abstract highly elongate vertical and horizontal calcite cemented concretions in pleistocene shallow marine and coastal eolian sandstones are mixtures of terrigenous sand and carbonate biogenic grains cemented to various degrees by low mg calcite petrographic and stable carbon and oxygen isotopic data support the earlier hypothesis of mazzanti and parea 1979 that vertically oriented concretions formed by the precipitation of vadose meteoric water percolating downward toward the water table and that horizontal concretions were precipitated from phreatic groundwater flowing toward the coast many vertical concretions started growth as rhizocretions composed of micrite but enlarged and coalesced when equant sparry calcite was precipitated from percolating vadose water horizontal concretions cemented entirely by subequant calcite spar have coalesced into nearly completely cemented beds decimeter scale domains of curved horizontal concretion elements reflect the influence of adjacent phreatic flow domains each with their own particular flow paths aragonite and high mg calcite shells in the sands were the main source of carbon in calcite cement isotopically depleted 13c values of bulk samples 6 to 8 5o oo v pdb however require the input of a light carbon source probably soil co2 18o values of bulk samples are compatible with cementation chiefly by meteoric water at temperatures between 7 and 22 c the values are typical of air and inferentially groundwater temperatures today

vermiculations from karst caves the case of pertosa auletta system italy abstract unlike the spectacular speleothems that can often be found in numerous caves vermiculations are rather unassuming formations whose origin and evolution still subject of several heated debates in order to provide a quantitative basis for the understanding of the nature and evolution of vermiculations in karst environments the geochemical properties of one of the most important karst systems of southern italy the pertosa auletta cave were studied through a comprehensive approach which included elemental mineralogical and microscopy analyses the chemical element abundances mineral composition and microstructure of the vermiculations covering the entire range of morphologies and colours observed in the case study cave were investigated thus providing the first quantitative record of these traits the vermiculations presented exceptional diversity in their morphology colour chemical and mineral composition with it being due to exogenous determinants such as the deposition of stream sediments or organic matter as well as the development of photoautotrophic communities they were invariably composed of calcite associated to quartz as well as clays and other secondary minerals the formation of which may be biologically mediated this occurrence and the evidences of microbial activity observed through dissolution traces support the possible involvement of biogenic processes in vermiculation development

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

the role of vaterite and aragonite in the formation of pseudo biogenic carbonate structures implications for martian exobiology abstract a simple synthesis of various forms of calcium carbonate with spherical and floral morphologies is reported vaterite formation occurs at 25 c aragonite at 70 c and calcite at about 80 c these are produced when co 2 is reacted with an aqueous solution of calcium chloride in the presence of ammonia these conditions may have existed at the surface of mars in the past leading us to conclude that such mineral formations may be common there although the initial phases are modified over time with changing temperature and pressure conditions they still influence the final morphology of the carbonates observed a comparison of these structures with those found in the martian meteorite alh84001 suggests but does not confirm a non biogenic origin for the alh84001 carbonates

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

nannobacteria as a by product of enzyme driven tissue decay spheroidal features 50 to 200 nm in size and found in sedimentary rocks have been described as nannobacteria the idea that they are minute fossilized life forms and especially the discovery of such features in martian meteorite alh84001 sparked a lively debate with regard to identification of ancient microbial life because biologists consider 200 300 nm to be the lower viable size limit for microorganisms an alternative explanation is needed for features that have been described as nannobacteria by geologists we report here on tissue decay experiments that produced abundant proteinaceous spheroids in the size range of nannobacteria described as nannoballs in the remainder of this paper experimental conditions were comparable to those found in earth9s surface sediments and diagenetic mineralization of these spheroids may be a common process for preservation of nannoballs that are observed in the rock record

nanometer scale features in dolomite from pennsylvanian rocks paradox basin utah abstract scanning electron microscopy reveals an association between early dolomite in the pennsylvanian desert creek paradox fm and small approximately 0 1 m nanometer scale textures termed nannobacteria three diagenetically distinct dolomites are present early dolomite limpid dolomite and baroque dolomite in this study only the early dolomite contained nanometer scale features these textures occur as discrete balls and rods clumps of balls and chains of balls precipitation experiments demonstrate that these textures may be the result of precipitation in an organic rich micro environment the presence of these nanometer scale textures in pennsylvanian rocks suggests that these early dolomites precipitated in organic rich bacterial environments

the formation of antitaxial calcite veins with well developed fibres oppaminda creek south australia abstract of the several vein types with elongate crystals we distinguish a class of veins with well developed fibres exposed at oppaminda creek south australia these calcite veins are characterised by very limited competition between growing crystals which leads to the development of fibrous crystals with smooth boundaries and which can attain extreme length width ratios fibres are often curved and track the opening trajectory the veins are also characterised by their outwards antitaxial growth starting from a narrow median zone these median zones contain wall rock inclusions and a distinctly different non fibrous internal microstructure such veins continue growing as long as extension is suitably oriented relative to the vein orientation multiple cross cutting vein sets can thus grow simultaneously and can together track over 90 rotation of the fibre growth direction the veins formed by calcite precipitation on both their outer surfaces we suggest that the term antitaxial should be redefined as applying only to those veins that have two simultaneous growth planes at their outer surfaces antitaxial veins grow without further fracturing which sets them apart from other veins that grew by precipitation inside a crack and which only have one single growth plane at the time the veins at oppaminda creek are about 585 ma in age and therefore formed at an estimated 4 6 km depth scanning electron microscope observations revealed about 1 m sized structures which we interpret as fossils of microbes that lived inside the veins at the time of their formation and which may even have played a role in the vein formation these structures would represent the first finds of fossilised life forms of such a combined age and depth

the possible role of nannobacteria dwarf bacteria in clay mineral diagenesis and the importance of careful sample preparation in high magnification sem study abstract bacterial textures are present on clay minerals in oligocene frio formation sandstones from the subsurface of the corpus christi area texas in shallower samples beads 0 05 0 1 m in diameter rim the clay flakes at greater depths these beads become more abundant and eventually are perched on the ends of clay filaments of the same diameter we believe that the beads are nannobacteria dwarf forms that have precipitated or transformed the clay minerals during burial of the sediments rosettes of chlorite also contain after hcl etching rows of 0 1 m bodies in contrast kaolinite shows no evidence of bacterial precipitation we review other examples of bacterially precipitated clay minerals a danger present in interpretation of our earlier work and much work of other is the development of nannobacteria looking artifacts caused by gold coating times in excess of one minute we strongly recommend a 30 second coating time bacterial growth of clay minerals may be a very important process both in the surface and subsurface

jurassic septarian concretions from nw scotland record interdependent bacterial physical and chemical processes of marine mudrock diagenesis septarian concretions in the staffin shales formation kimmeridgian isle of skye allow controls on concretion rheology and septarian cracking to be investigated stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite intergranular volumes range from 77 to 88 and calcite 13c and 18o values in most concretion bodies range from 10 0 to 17 3 and 0 3 to 0 6 respectively consistent with rapid and pervasive cementation in marine pore fluids septarian rupture occurred during incipient cementation with a sediment volume reduction of up to 43 crack lining brown fibrous calcite records pore fluid re oxygenation during a depositional hiatus followed by increasing fe content and 13c related to bacterial methanogenesis brown colouration results from an included gel like polar organic fraction that probably represents bacterially degraded biomass a new hypothesis for concretion growth and septarian cracking argues that quasi rigid proto concretions formed via binding of flocculated clays by bacterial extracellular polysaccharide substances eps this provided rheological and chemical conditions for tensional failure subcritical crack growth volume contraction calcite nucleation and incorporation of degraded products into crack lining cements bacterial decay of eps and syneresis of host muds provided internal stresses to initiate rupture at shallow burial development of septarian shrinkage cracks in muds is envisaged to require pervasive in situ bacterial colonization and to depend on rates of carbonate precipitation versus eps degradation and syneresis subsequent modification of septarian concretions included envelopment by siderite and calcite microspar hydraulic fracturing associated with cretaceous shallow burial or palaeogene uplift and cementation by strongly ferroan yellow sparry calcite that records meteoric water invasion of the host mudrocks an abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products and 13c data suggest a predominantly methanogenic bicarbonate source however the wide 18o range for petrographically identical cement 1 3 to 15 6 is difficult to explain

calcite moonmilk crystal morphology and environment of formation in caves in the italian alps abstract calcite moonmilk which is a cave deposit formed of calcite crystals and water is found in many caves in the italian alps these modern and ancient deposits are formed of fiber calcite crystals 50 500 nm wide and 1 to 10 m long and polycrystalline chains that have few crystal defects radiocarbon dating indicates that most moonmilk deposits in these caves are fossil and that for most precipitation ceased 6400 cal years bp at the end of the mid holocene hypsithermal in the caves of the italian alps the optimal conditions for formation of calcite moonmilk are 1 a temperature range of 3 5 5 5 c 2 low discharge volumes of seepage waters that are slightly supersaturated sical 0 0 to 0 2 and 3 relative humidity that is at or close to 100 microbial activity apparently did not play an active role in the formation of the calcite moonmilk conditions for moonmilk formation are typically found in caves that are located beneath land surfaces which are soil covered and support a conifer forest precipitation of the fiber calcite crystals apparently involved very slow flow of slightly supersaturated fluids the fact that moonmilk appears to form under a narrow range of environmental conditions means that this cave deposit has potential as a paleoclimatic indicator in high alpine karst areas

microbial biscuits of vaterite in lake issyk kul republic of kyrgyzstan abstract microbial biscuits of vaterite a polymorph of caco3 were found in lake issyk kul republic of kyrgyzstan four sections were defined from the inner part to the outer part of these microbial biscuits 1 a nucleus made up of coated discrete bacterial forms 2 a massive coating attributed to the calcification of the mucilaginous sheath of the bacterial community 3 a thick lamina composed of large fibers of vaterite and 4 a discontinuous external coating incorporating foreign elements such as diatoms the origin of these microbial biscuits is attributed to bacterial activity the vaterite formation seems to be related to the hexagonal structure of the mucilaginous sheath and to the inhibitor role of the phosphorous present in the water during calcite precipitation

effects of sem preparation techniques on the appearance of bacteria and biofilms in the carter sandstone abstract when biofilms aggregations of bacteria and extracellular polymer secretions in samples from the carter sandstone of alabama were prepared for scanning electron microscopy sem using different dehydration techniques the organic material had visibly different textures and distributions in order to assess whether the variation was attributable to sample preparation or to inherent biofilm heterogeneity each of five techniques were tested 3 to 10 times on small 1 cm pieces of the carter sandstone containing either a strain of bacteria cultured from and reintroduced into the rock or an in situ biofilm grown by injection of nutrients through core samples the techniques tested were 1 air drying alone 2 fixation in 10 glutaraldehyde with air drying 3 ethanol dehydration with hexamethyldisilazane hmds drying 2 5 glutaraldehyde ethanol dehydration and hmds 4 ethanol dehydration with critical point drying and 5 ethanol and acetone dehydration with critical point drying unpreserved control samples were either imaged wet in an environmental scanning electron microscope esem or vacuum dried for sem observations were based on sem microscopy of over 60 samples and study of over 150 photomicrographs in both experiments the original morphology of individual bacteria was best preserved by ethanol dehydration with hmds drying ethanol dehydration with critical point drying or ethanol acetone dehydration with critical point drying critical point drying preserved bacteria but stripped away mucilaginous material revealing filamentous structures within the biofilm these filaments along with masses of microspheres nannobacteria and the smooth mucilaginous outer layer also occur in wet samples studied by esem and are therefore not dehydration artifacts however different sample preparation techniques accentuated different components of the heterogeneous biofilm thus resulting in vastly different textures the cultured bacteria produced a biofilm that had a different surface texture and was more susceptible to sample preparation artifacts than the in situ biofilm use of more than one sample preparation technique is recommended in order to avoid bias

mobilization and retardation of reduced manganese in sandy aquifers column experiments modeling and implications abstract manganese enrichment is common in various sedimentary environments e g deep ocean floor shallow sedimentary environments where the overlying water column is oxic and phreatic aquifers in which the mn aquatic geochemistry is controlled by redox conditions in many cases aquifers recharged by organic rich waters contain high amounts of dissolved mn 2 that was mobilized from sedimentary mn oxides during microbial oxidation of the organic matter under low oxygen conditions thus the identification and quantification of the processes controlling mn mobilization and speciation is of great practical importance as a geochemical tool for sustainable management of aquifers this study uses column experiments to quantify the role of adsorption and precipitation in retarding mn 2 mobilization in sandy aquifers under low oxygen conditions flow through columns were packed with pristine sandy sediment and were recharged by low oxygen artificial solutions containing different mn 2 concentrations outflow solutions from the column experiments were analyzed and simulated using a mn 2 transport reaction model the results were used to demonstrate the importance of adsorption on mn mobilization in three different aquifers the experimental data showed that adsorption of mn 2 on the column solids was the main control on the mn 2 breakthrough behavior nevertheless up to 20 of the mn that entered the experimental columns was precipitated as mnco 3 the rate of mnco 3 precipitation k p 0 04 h 1 was found to be 3 orders of magnitude slower than the rate of mn 2 adsorption k a 10 200 h 1 given the slow mineral precipitation kinetics the water flow rate is critical in determining the potential of mnco 3 precipitation in immobilizing mn within an aquifer a scale up of the mn retardation time found in the column experiments to natural aquifer conditions suggests that adsorption is responsible for the prolonged retardation of mn 2 observed in three different sandy aquifers an important practical conclusion of this study is that the environmental response to perturbation in the hydro geochemical regime of an aquifer might be delayed for several decades

kopara in polynesian atolls early stages of formation of calcareous stromatolites widespread modern calcareous stromatolites known as kopara in the vernacular language on the tuamotu archipelago have been found accreting on the bottom of shallow generally 1 m depth lakes located on the rims of these french polynesian atolls they are flat gelatinous sediments several tens of centimetres thick with lamination comprised of vertically alternating red organic rich and white carbonate rich millimetre thick laminae they originate from benthic microbial communities mainly composed of cyanobacteria generally dominated by the genus phormidium the living cyanobacteria occupy only the top 1 3 cm of the deposit the red organic matter below being made of remnants of the dead microbes essentially of polysaccharide microfibrils inherited from the sheaths and arranged into a three dimensional network enclosing pores ranging from a few tens of angstroms to a few micrometres wide the carbonates are predominantly high mg calcite 9 19 mole mgco3 which precipitated as micron size bunches within the pores on walls of the organic network it is sometimes accompanied by aragonite less than 22 of the total mineral fraction when present and lesser high mg calcite allochthonous bioclasts which occasionally form up to few centimetres thick detrital intercalations the pore waters are variable mixtures of freshwater rain or ground water and sea water from the ocean or lagoon which are feeding waters of the lakes their chemistry deviate from a straight mixture gradient with respect to ca2 mg2 and alkalinity under the influence of local calcification and bacterial processes e g ammonia production sulphate reduction within the sediments it is hypothesized that the calcification is initiated at carboxylic sites on the walls of the polysaccharide network the pores acting as confining organic compartments with increased internal supersaturation lamination is suggested to be due to the combined effects of the stratification of the microbial activity of the deposits and alternations of fresh and saline periods within the lakes lacustrine environments on oceanic atolls are found to be important habitats of modern microbialite formation

nanometre scale spheroids on sands vulcano sicily possible nannobacterial alteration spheroids in the size range of 30 200 nm coat sand grains on sediments around the island of vulcano they occur as single individuals as ball shaped clumps resembling biological colonies with radiating chains of bodies and eventually merge into sheets in which the individual nannobacteria are no longer evident rarely they appear to bore into the glass grains older rocks are composed mainly of closely packed nanospheroids these spheroids are believed to be nannobacterial cells based on their resemblance to nannobacteria found in other surficial environments and their occurrence in colony like groups if so nannobacteria play a very important role in the destruction of volcanic materials on vulcano

seep carbonates and preserved methane oxidizing archaea and sulfate reducing bacteria fossils suggest recent gas venting on the seafloor in the northeastern south china sea seep carbonates formed by the synergistic metabolism of methane oxidizing archaea moa and sulfate reducing bacteria srb have been found in many places worldwide but have not been found to date in the south china sea mud volcanoes and shale diapirs have been reported in the south china sea however and microscope and geochernical analysis of carbonates dredged where bottom simulating reflectors bsr suggest the presence of gas hydrate on the northeastern continental slope of the south china sea suggest that the carbonates are hydrocarbon seep related carbonates the carbonates we dredged are chimney like and preserve moa srb fossils their very light carbon isotopic compositions 51 25 to 51 76 parts per thousand suggest that their carbon was derived from microbial methane oxidization these seep carbonates and their preserved moa srb fossils imply gas venting has occurred recently on the seafloor in the northeastern continental slopes in the south china sea c 2005 elsevier ltd all rights reserved

the nature of fossil bacteria a guide to the search for extraterrestrial life in an attempt to establish reliable criteria for the identification of potential fossil life in extraterrestrial materials the fossilizable characteristics of bacteria namely size shape cell wall texture association and colony formation are described and an overview is given of the ways in which fossil bacteria are preserved as compressions in fine grained sediments preservation in amber permineralized by silica replacement by minerals such as silica pyrite fe mn oxides calcite phosphate and siderite or as molds in minerals the problem of confounding minerally replaced bacteria with non biological structures having a bacterial morphology is addressed examples of fossilized bacteria from the early archaean through to the recent are used to illustrate the various modes of preservation and the morphology of fossil bacteria

nannobacteria and the precipitation of carbonate in unusual environments abstract nannobacteria are abundant not only in normal marine limestones but also in other environments such as continental caliches fresh water streams springs water pipes caves etc cells are typically 50 to 200 nm in diameter