As a follow-on to existing exobiology activities in low earth orbit, ESA commissioned a Science Team in the period late 1996 to mid 1998 to assess the interest of 'search for life' exobiology research in a European context. In particular the Science Team has concentrated on the search for life in the Solar System and more recently on possible European activities related to the search for extinct life on Mars. The Science Team recommended the development of a multi-user Exobiology package employing a sub-surface distribution system and various analytical instruments for in-situ analysis on Mars. This paper also discusses the required technical developments and the possible upcoming mission opportunities. Some considerations on the performance of exobiological research during future human missions to Mars are also given.

Martian Landers have limited mass, volume, and power resources. A number of potential 'low resource' techniques will be described for astrobiology on Mars. These include consideration of alternative power systems for obtaining subsurface rock samples and the adaptation of nano- technology and miniaturized for use in detecting organic molecules on Mars. The techniques will be discussed.

The proposed Beagle 2 lander for ESA's 2003 Mars Express mission will be described. The aim of Beagle 2 will be to search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize a small rover equipped with a mechanical and grinder to obtained samples from below the surface, under rocks, and inside rocks. Samples will be returned to the lander for analysis. Analysis performed by Beagle 2 will include examination of samples with an optical microscope and APX and Mossbauer Spectrometers as well as a search for organics and a measurement of their isotopic composition. The lander systems design as well as the experiment configuration will be described.

Many objections have been raised to challenge a biological interpretation of the 1976 Viking Mission Labeled Release (LR) life detection experiment on Mars. Over the years, they have dwindled in the face of the failure of experiments and theories to demonstrate a nonbiological alternative. Recently, NASA's chief scientist, responding to the rapidly accumulating knowledge about life in extreme environments, reduce the remaining obstacles to a single one: the lack of liquid water. A model is consistent with the thermodynamics of the triple point of water. Viking and Pathfinder meteorological data are congruent with the model, as are Viking Lander images of deposits of water ice-frost and snow on the ground. The amounts of soil moisture predicted by the model are within the moisture content range of terrestrial soils in which the LR detected living microorganisms. The last objection to a biological interpretation of the LR Mars data is thus met. Consequential recommendations for the near-term planetary program are made.

The Dead Sea is a hypersaline terminal desert lake. Its water contains about 340 g/l total dissolved salts. Divalent cations dominate in the brine, which presently contains about 1.89 M magnesium and 0.44 M calcium, n addition to about 1.6 M sodium and 0.2 M potassium. The main anions are chloride and bromide. The pH of the brine is about 6.0, and its water activity was estimated at about 0.66. The lake is saturated with respect to sodium chloride. The negative water balance in recent years caused a mass precipitation of halite, with a concomitant increase in the relative concentrations of divalent cations. In spite of the fact that molar concentrations of divalent cations are strongly inhibitory to most halophilic and halotolerant microorganisms, the Dead Sea is inhabited by a variety of microorganisms. These include halophilic Archaea, well adapted to growth at high magnesium concentrations, unicellular green algae and a few species of halophilic Bacteria. Dunaliella, being the sole primary producer in the lake, does not grow in undiluted Dead Sea water. However, when the upper water layers become diluted by more than 10 percent as a result of winter rain floods, mass blooms may develop, followed by mass development of red halophilic Archaea, which thrive on the organic material produced by the algae. During the often prolonged periods between the bloom events, during which the salinity of the brines is high and halite precipitates, a small community of Archaea remained present in a state of little activity, but ready to resume growth as soon as a suitable source of organic material becomes available.

Europa, the ice-covered satellite of Jupiter, is currently the most favorable site for the search of extraterrestrial life. Hydrothermal vents on the Earth's sea floor have been found to sustain life forms that can live without solar energy. Similar possible volcanic activity on Europa, caused by its interaction with Jupiter and the other Galilean satellites, makes this Jovian moon the best target for identifying a separate evolutionary line. This search addresses the main problem remaining in astrobiology, namely, the quest for discrete, or 'parallel' evolutionary lines in the universe. We explore ideas related to Europa's possible biological activity, particularly its likely degree of evolution. We have conjectured that evolution may have occurred in Europa and that the experimental test of such a conjecture is feasible. A lander space craft capable of penetrating the Europan surface ice-layer does not seem beyond present technological capabilities. Although difficult instrumentation issues are involved, we have initiated the discussion of what would seem to be a reasonable biological experiment. The possibility of detecting biomolecules on the ice surface of Europa has recently been made by others. A possible mechanism for bringing biomolecules to Europa's surface will be critically reviewed.

Many investigators regard Antarctica as a model for solution of such problems as search of life on other planets, the quarantine in planets, and at the Earth during interplanetary contacts. It is also a good natural experiment for studying the phenomenon of microbial long- term anabiosis. Remoteness from the regions of intensive anthropogenic effects, low stable temperature and reliable protection of ancient ice horizons against subsequent environmental changes make Antarctic ice sheet an ideal object for methodological works necessary for investigation of various problems of exobiology. Investigations of ice bodies in attempts to find there any possible form of life has an advantage over similar studies of other cosmic solids because microorganisms, spores, plant pollen, unicellular algae, and other inclusions rather easily release from the melted ice and their investigation by different methods depends only on the well thought-out techniques. Special techniques of aseptic sampling while drilling at Vostok station and analysis of these samples by different methods have provided evidence for the existence of viable microorganisms in very ancient layers of the ice sheet. The relationship between quantitative distribution of microbes at different horizons of the ice column with the Earth's climate fluctuations at the time of these layers formation was also demonstrated.

Nanobacteria are the smallest cell-walled bacteria, only recently discovered in human and cow blood and in commercial cell culture serum. In this study, we identified with energy-dispersive x-ray microanalysis and chemical analysis that all growth phases of nanobacteria produce biogenic apatite on their cell envelope. Fourier transform IR spectroscopy revealed the mineral as carbonate apatite. Previous models for stone formation have lead to a hypothesis that an elevated pH due to urease and/or alkaline phosphatase activity are important lithogenic factors. Our results indicate that carbonate apatite can be formed without these factors at pH 7.4 at physiological phosphate and calcium concentrations. Due to their specific macromolecules, nanobacteria can produce apatite very efficiency in media mimicking tissue fluids and glomerular filtrate and rapidly mineralizing most of available calcium and phosphate. This can be also monitored by ⁸⁵Sr incorporation and provides a unique model for in vitro studies on calcification. Recently, bacteria have been implicated in the formation of carbonate (hydroxy)fluorapatite in marine sediments. Apatite grains are found so commonly in sedimentary rocks that apatite is omitted in naming the stone. To prove that apatite and other minerals are formed by bacteria would implicate that the bacteria could be observed and their actions followed in stones. We have started to approach this in two ways. Firstly, by the use of sensitive methods for detecting specific bacterial components, like antigens, muramic acid and nucleic acids, that allow for detecting the presence of bacteria and, secondly, by follow-up of volatile bacterial metabolites observed by continuous monitoring with ion mobility spectrometry, IMCELL, working like an artificial, educatable smelling nose. The latter method might allow for remote real time detection of bacterial metabolism, a signature of life, in rocks via fractures of drillholes with or without injected substrate solutions. Nanobacteria may provide a model for primordial life-forms, such as replicating clay crystallites in a sandstone, where minerals and metal atoms associated to membranes, may play catalytic and structural roles reducing the number of enzymes and structural proteins needed for life. Such simple metabolic pathways may support the 10,000-fold slower growth rate of nanobacteria, as compared to the usual bacteria. They may also explain the endurability of this life-form in extreme environmental conditions. Altogether such properties do suggest that nanobacteria may have evolved from environmental sources, such a shot springs, to take advantage of the steady-state calcium and phosphate supply of the mammalian blood. Based upon our findings of nanobacteria, a novel theory for the early development of life, based on apatite-mediated chemistry on membranes selecting itself for its own catalytical machinery, is presented.

Existence of nanobacteria received increasing attention both in environmental microbiology/geomicro-biology and in medical microbiology. In order to study a production of nanoforms by typical bacterial cells. Effects of different physical factors were investigated. Treatment of bacterial cultures with microwave radiation, or culturing in field of electric current resulted in formation a few types of nanocells. The number and type of nanoforms were determined with type and dose of the treatment. The produced nanoforms were: i) globules, ii) clusters of the globules--probably produced by liaison, iii) nanocells coated with membrane. The viability of the globules is an object opened for doubts. The nanocells discovered multiplication and growth on solidified nutrient media. The authors suggest that formation of nanocells is a common response of bacteria to stress-actions produced by different agents.

Nanobacteria show high resistance to gamma irradiation. To further examine their survival in extreme conditions several disinfecting and sterilizing chemicals as well as autoclaving, UV light, microwaves, heating and drying treatments were carried out. The effect of antibiotics used in cell culture were also evaluated. Two forms of nanobacteria were used in the tests: nanobacteria cultured in serum containing medium, and nanobacteria cultured in serum-free medium, the latter being more mineralized. Nanobacteria, having various amounts of apatite on their surfaces, were used to analyze the degree of protection given by the mineral. The chemicals tested included ethanol, glutaraldehyde, formalin, hypochlorite, hydrogen peroxide, hydrochloric acid, sodium hydroxide, detergents, and commercial disinfectants at concentrations generally used for disinfection. After chemical and physical treatments for various times, the nanobacteria were subcultered to detect their survival. The results show unique and wide resistance of nanobacteria to common agents used in disinfection. It can also be seen that the mineralization of the nanobacterial surface furthermore increases the resistance. Survival of nanobacteria is unique among living bacteria, but it can be compared with that observed in spores. Interestingly, nanobacteria have metabolic rate as slow as bacterial spores. A slow metabolic rate and protective structures, like mineral, biofilm and impermeable cell wall, can thus explain the observations made.

The mechanisms of dental pulp stone formation are still largely unknown. Pulp stones are mainly composed of carbonate apatite. Only few experimental reports have elucidated the potential of some selected bacteria to produce apatite under in vitro conditions using special calcification media. The tested stone forming bacteria were, in fact, often better known for their cariogenic potential. Our preliminary work with 18 dental pulp stones from Turkey, selected only by severity of the stone formation, indicated the presence of nanobacterial antigens in the demineralized stones. Furthermore, high incidence of kidney stones and gall stones in the patient group and in their parents was found. This raises the implication that nanobacteria may enter the body also via oral route, in addition to the parenteral and transplacental routes. The role of nanobacteria in dental pulp stone formation was further studied by following nanobacterial colonization and mineral formation on human tooth in vitro. Two molar teeth, one having pulp stone and one without, were vertically cut into two pieces, sterilized by autoclaving and incubated with or without nanobacteria in DMEM. Electron microscopic observations indicate that nanobacteria can cause apatite stone formation on tooth surface. The sever from of dental pulp stone formation might be associated with nanobacteria. This form of dental disease results in loss of teeth due to osteolytic processes. This addresses the necessity for a study on unconventional mineral-forming bacteria as a cause for human diseases.

The formation of discrete and organized inorganic crystalline structures within macromolecular extracellular matrices is a widespread biological phenomenon generally referred to as biomineralization. Recently, bacteria have been implicated as factors in biogeochemical cycles for formation of many minerals in aqueous sediments. We have found nanobacterial culture systems that allow for reproducible production of apatite calcification in vitro. Depending on the culture conditions, tiny nanocolloid-sized particles covered with apatite, forming various size of aggregates and stones were observed. In this study, we detected the presence of nanobacteria in demineralized trilobit fossil, geode, apatite, and calcite stones by immunofluorescence staining. Amethyst and other quartz stones, and chalk gave negative results. Microorganisms are capable of depositing apatite outside the thermodynamic equilibrium in sea water. We bring now evidence that this occurs in the human body as well. Previously, only struvite kidney stones composed of magnesium ammonium phosphate and small amounts of apatite have been regarded as bacteria related. 90 percent of demineralized human kidney stones now screened, contained nanobacteria. At least three different distribution patterns of nanobacteria were conditions, and human kidney stones that are formed from small apatite units. Prerequisites for the formation of kidney stones are the supersaturation of urine and presence of nidi for crystallization. Nanobacteria are important nidi and their presence might be of special interest in space flights where supersaturation of urine is present due to the loss of bone. Furthermore, we bring evidence that nanobacteria may act as crystallization nidi for the formation of biogenic apatite structures in tissue calcification found in e.g., atherosclerotic plaques, extensive metastatic and tumoral calcification, acute periarthritis, malacoplakia, and malignant diseases. In nanaobacteria-infected fibroblasts, electron microscopy revealed intra- and extra-cellular needle-like crystal deposits, which were stainable with von Kossa stain and resemble calcospherules found in pathological calcification. Thus bacteria-mediated apatite formation takes place in aqueous environments, in humans and in geological sediments.

The carbon in Allende consists of balls ranging form 30 to 150 nm in diameter.Most are spheres, but some ovoid to worm- like forms occur. Grape-like clumps and rosary-like chains are the most dramatic mimics of terrestrial bacterial colonies. We propose that the carbon balls in Allende represent roasted corpses of nanobacteria because of their resemblance to nanobacteria on earth.

With the paleobiological evidence from the currently known Archaean rock record at hand, the existence on Earth of microbial ecosystems as from about 3.8 Ga ago so firmly established as to be virtually unassailable. However, important details pertaining to the establishment and early history of life on this planet call for further elucidation. Residual questions primarily center around (1) the impairment of relevant information in the oldest record that bears a metamorphic overprint, (2) the apparent non- documentation in the Archaean record of an archaebacterial lineage expected to form the base of the phylogenetic tree of terrestrial life, (3) the possible role of impact interference with early biological evolution, and (4) problems of the time scale of early organic evolution as exemplified by the unheralded appearance about 3.8 Ga ago of microbial life on the organizational level of the prokaryotic cell.

A suite of previously unknown microfossils and related biogenic structures has been revealed in some of the oldest sediments on Earth using scanning electron microscopy. High resolution scanning electron microscopy of HF-etched, biolaminated charts has brought to light a variety of small fossil coccoid and rod-shaped bacteria and associated fossil biofilms containing bedding planes. These microfossils have ben completely replaced by minerals. This vastly improved early Archaean microfossil database sheds new light on the diversity of life on Earth relatively soon after the cessation of heavy bolide bombardment at about 3.8 Ga. This is the critical period when life may have been able to develop on Mars and these early Archaean terrestrial microfossils will serve as valuable analogues for possible extraterrestrial life.

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.

The Vend-Early Cambrian phosphorite stockpiles compose about 20% ofthe world's phosphorites. The most extensive ancient phosphorite deposits are located in Central Asia, in South China, Northern Mongolia (Khubsugul) and South Kazakhstan (Karatau). According to palaeomagnetic data, at the beginning of the Cambrian these regions were restricted to low latitudes and, consequently, to the equatorial climatic belt. The time of accumulation of the most of above mentioned deposits falls within the Tommotian, which is the earliest stage of the Early Cambrian. These deposits are dated using the fossils incorporated in the phosphorites. We studied the structure of the Khubsugul phosphorites (I). Khubsugul phosphorites are represented by granular or structureless aphanite rocks refered to microgramed type. Their genesis is often related to chemical phosphorus precipitation from level bottom waters in the vicinity ofupwelling zones (2).

The phylum Brachiopoda includes a small class Lingulata that first appeared in the Early Cambrian. These brachiopods were very numerous in the Lower Paleozoic, and still survive in the recent sea biota (five genera). Lmgulate shells consist of alternated organic and calcium phoshate layers, but lack calcium carbonate typical of another brachiopod class - Calciata. Calcium phosphate layers are composed of thin needle-like ciystallites enclosed in organic matrix. Thus the organics form more than half of the shell and, together with the soft body, it may be about three quarters of the entire organism. After the death the ungulate shells have undergone the intensive attack of microorganisms. According to Ch. Emig(1) data, the organic matter in recent Lingula shells near the bottom surface macerates and dissolves in a week, after that shells disappear. So the preservation of shells in fossils occur under certain conditions. Text below describes three different cases of shell preservation in fossils: due to intensive bacterial activities or, on the contrary, due to supressed bacterial work.

Precambrian microfossils were used for a comparison in the study of the microstructures in carbonaceous meteorites. As a result, three morphological categories could be distinguished in the meteorite materials. Category 1- morphologies are such simple spheres and filaments that we can hardly be confident about biological assignments. Category 2-morphologies closely resemble structures known from laboratory experiments and thus should continue to be treated as non-biogenous. Morphologies of the third category are quite comparable to terrestrial microfossils in their preserved features and thus might be biogenous. Our observations suggest that carbonaceous meteorites are heterogenous in composition and contain particles from different extraterrestrial sources and of different ages.

Determining how, where and when life as we know it originated are three of the most challenging questions confronting scientists. The fact that the Earth has likely been infected with life as far back in time as the rock record extends makes it almost futile to search for life's precursors on this planet. There is no definitive way to distinguish structures of the key biomonomers essential for life's origin from the remnants of once living organisms that have accumulated or recycled through the geosphere for approximately the past 4 billion years. While extraterrestrial materials that have fallen to Earth have been probed for clues to life's origin elsewhere in the solar system, these materials also, upon impact, become part of the Earth system. Thus, their subsequent contamination via exchange with terrestrial biota is always a realistic possibility. Exploring other planetary bodies is the third possible way to trace life's origin or the origin of organic compounds that preceded life. However, it is almost impossible to expect that manned or unmanned probes will not to some extent infect the surfaces of these bodies during contact. We propose that one possible way to begin to distinguish abiotic compounds from biotic compounds as well as terrestrial vs. extraterrestrial compounds is an assessment of the stable isotope compositions of the light elements that comprise them relative to those of the substrates from which they were formed.

Scanning electron microscopy investigations carried out independently in the US and Russia have yielded further evidence of microfossils in meteorites. Numerous complex biomorphic microstructures representing possible microfossils have been found in interior surfaces of freshly broken samples of the Murchison, Orgueil, and Efremovka carbonaceous chondrites. Similar biomorphic forms were not encountered during comparable investigations of the Nikolskoye meteorite. Energy dispersive spectroscopy and link microprobe analysis provides elemental distribution indicating many of the microstructures have a carbon enhancement that is superimposed upon composition of the meteoritic matrix. The in-situ mineralized biomorphic microstructures found embedded in freshly fractured meteoritic surfaces are not considered to be recent surface contaminants.

A variety of microscope techniques have been used to study surficial phenomena on the fracture surfaces of the Martian meteorite ALH84001. The aim of the investigation was to determine the most useful microscopy methods in the search for morphological signs of biogenic activity. Emphasis was placed on scanning electron microscopy (SEM) using secondary, backscatter and cathodoluminescence modes combined with observation of samples at a variety of accelerating voltages. High resolution SEM imaging was compared with atomic force microscopy. These techniques revealed a number of structures of possible abiotic and biotic origin: (1) a large, fibrous-looking carbonaceous structure, (2) fine, flaky films coating pyroxene surfaces, (3) finely granular calcium carbonate deposit is associated with the fine film, and (4) lacy-structured, mineralized polymers on the pyroxene surface. Another sample contains further evidence of water-lain deposits in a cracked, iron oxide coat on a fracture surface.

The world of minerals, characterized by 3D infinite periodic distribution of atoms, coexists in nature with the world of structurally ordered hydrocarbons, which posses may features making them structurally similar to simplest organisms. In spite of the fact, that study of supermolecular ordering in solid hydrocarbons is at its dawn, nonbiogenic hydrocarbon organism-like forms have been found in many earthly and space objects.One prominent example is fibrous kerite crystal from crystallization voids in pegmatites. Kerite crystals show fibrous and cylindrical habits, frequently with spheres at the ends and an internal axial channel. Spiral-like individuals twisted in one direction as well as complex regeneration aggregates are frequently observed. Fibrous kerite crystal have elemental composition nearly identical to that of protein. They contain all chemical elements typical of the living matter and all elements- catalysts. Heating the crystals in the range from 20 to 600 degrees C resulted in release of a variety of hydrocarbon gases to the inner channels and environment. The crystals are distinguished by anomalously high contents of all 'protein' amino acids, which are synthesized from abiogenic components during crystallization. Protein self-assembly and evolution of some organismic functions described as biological ones are possible. We relied on fibrous kerite crystals to develop a model of a protobiological organism, genetic predecessor of biological life forms and propose a concept of hydrocarbon crystallization of life.

We discuss two new factors relevant to the dispersal of established life to hospitable and sterile planets. The first factor concerns the interstellar dispersal of viable microbes within the environment of old, metal-rich, open star clusters. We determine that these clusters present an excellent environment for the transfer of microbial life, since the likelihood of interstellar dispersal is enhanced: the stellar density on the order of 15 stars per pc^-3, which decreases the interstellar travel time and raises the probability of collisions between the microbes and planets. As well, the old open clusters remain bound for billions of years, a time scale sufficient for life to arise and be dispersed amongst component starts, after which the open cluster are disrupted, and the component stars are dispersed throughout the Galactic disk. The second factor concerns the probabilistic dynamics of local establishment once an invading propagule is deposited on a planet's surface. We describe a population model relevant to the initial dynamics of invasion for a group of N initial colonists, and discuss processes that affect the long-term persistence of established colonizing groups, including temporal and spatial environmental fluctuations, mutation, and adaptation. This model places a strong constraint on the panspermia hypotheses: not only must microbes survive the hazards associated with transport through interplanetary and interstellar space, but we determined that demographic stochasticity can quickly lead to the extinction of small groups of invading microbes, even if the environment is hospitable for colonization.

Air samples are to be collected at various altitude sin the stratosphere using balloons flown form Hyderabad, India. The samples will be passed through sterile micropore filters, after which the filters will be analyzed using voltage sensitive lipophilic dyes to detect the presence of either active or non-active cells. Organisms detected in this manner will be studied using static mass spectroscopy to establish isotropic ratios ¹³C/¹²C and D/H, which would distinguish between terrestrial and extraterrestrial cells.

Panspermia, an ancient theory, was revived in its modern form by two of the present authors (H-W) in a series of publications over the period 1977 to the present day. Unpopular at first, it is now slowly gaining popularity and is coming to be discussed, albeit with a measure of apprehension, as a serious scientific possibility. A brief resume will be given of the modern scientific case for panspermia, indicating that astronomical, geological and biological evidence is moving slowly in the direction of a paradigm shift.

The central regions of galaxies could provide the most promising venues for the large-scale synthesis of prebiotic molecules by Miller-Urey type processes.Exploding supermassive stars would produce the basic chemical elements necessary to form molecules in high-density mass flows under near-thermodynamic conditions. Such molecules are then acted upon by X-rays in a manner that simulates the conditions required for Miller-Urey type processing. The Miller-Urey molecular products could initially lead to the origination and dispersal of microbial life on a cosmological scale. Thereafter the continuing production of such molecules would serve as the feedstock of life.

Capsular Cryptococcus spp. dominate in desert soils. The most extreme conditions are encountered by Cryptococcus vishniacii which dominates in the arid highlands of the Ross desert of Antarctica by virtue of its ability to grow at low temperatures, minimal nutritional requirements, tolerance of low population densities, and survival skills, although this species is neither osmo-nor halotolerant, characters which are associated with higher energy requirements.

The conjecture that bacteria, or, more widely microbes are capable ofbemg preserved like large organisms as fossils seemed very improbable as late as the 1960's. Reports ofbacterial remains discernible in sedimentary rock were invariably called into question.There were substantial grounds for that: bacterial morphology is normally little expressed, and cocci or micron-sized bacilli can be easily imitated by mineral formations. An exception was made for flint rock, primarily silicified parts of stromatoliths.

Cyanobactenal mats have been extensively studied during the past decades. There are all reasons to believe that these highly productive systems might have contributed to the formation of deposits of some combustible mineral raw materials. It is generally accepted that stromatolites are nothing but ancient litified mats.

The evolution of biological complexity on Earth has taken many pathways. Prokaryotes were the only life for the first 2000 million years (My); protistan eurkaryotes evolved through symbioses with preexisting prokaryotes and radiated into a variety of environments during the next 200 My. These protist photosynthesized and probably lived in both benthic and pelagic habitants where light was available. Heterotrophic protists were surely extant then too, but they left no fossil record until just 550 Ma. The algae began to diversify in the Neoproterozoic after 1000 My of rather static evolutionary development. Between 1000 and 530 Ma, algal diversity increased and decreased in response to oceanographic and climatic changes, probably associated with plate tectonic motions and ice ages. In the last part of the Neoproterozoic soft-bodied multicellular eukaryotes appeared and diversified somewhat. Study of modern trace makers, the taphonomy of living cnidarians, and molecular phylogenies of living basal metazoans indicates that the complexity represented probably includes mostly diploblastic levels along with possible metazoans indicates that the complexity. Algal protists diversified and the morphology of their cysts became intricate, while heterotrophic protists developed skeletons, as did the Metazoa. Over 15 hypotheses have been suggested to account for this radiation, or 'explosion' of Cambrian organisms, but none is clearly acceptable now. The geochemical evidence indicates that oceanographic circulation increased, upwelling may have become common seasonally and geographically, and this may well have increased productivity and the trophic complexity of both the benthic and pelagic marine biota.

Recent findings strongly suggest that a well developed biosphere was present on Earth 3800 million years ago. Consequently life's origin must be considerably older. The remaining time span of Earth history appears to be too short for all the processes necessary for the evolution from a simple compound to a perfect organism. An alternative explanation implies that the prebiotic products required for the formation of life are of extraterrestrial origin and were imported from space with the early planetesimal in-fall that had struck the Earth prior to 3800 million years. Recent observations have detected a great variety of organic molecules in the interstellar clouds of our galaxy. Several molecules hitherto identified can be considered as precursors of the most biochemical compounds and structural components present in living systems. That prebiotic chemistry has been brought from interstellar space to Earth is an intriguing possibility. Cosmic dust can reach the Earth gently without being destroyed. Open to question is the condition in which the organics came down: were they at a prebiotic stage or in a biotic condition as originally postulated by Svante Arrhenius.

Chemolithotrophic iron oxidation by Thiobacillus ferrooxidans and other iron oxidizing thiobacilli produce an Fe(III) sulfato complex that polymerizes as x-ray amorphous filaments approximately 40 nm in diameter. The precursor complex in solutionis seen by ATR-FTIR spectroscopy to have a sulfate spectrum resembling the v₃ and v₁ vibrational modes of the precipitated polymer. Chemically similar precipitates prepared by oxidation of acid ferrous sulfate with hydrogen peroxide have a different micromorphology, higher iron/sulfur ratio and acid solubility than the bacterial product. They possess coalescing globular microstructures composed of compacted micro-fibrils. Scanning electron microscopy and diffuse reflectance FTIR show the formation of iron polymer on the surface of immobilized cells of T. ferrooxidans, oxidizing iron during the corrosion of steel. Although spatially separated form the steel coupons by a membrane filter, the cell walls become covered with tufts of amorphous hydrated Fe(III) sulfate. The metastable polymer is converted to crystalline goethite, lepidocrocite, and magnetite in that order, as the pH rises due to proton reduction at cathodic sites on the steel. The instability of the iron polymer to changes in pH is also evidenced by the loss of sulfate when washed with lithium hydroxide solution at pH 8. Under those conditions there is little change in micromorphology, but restoration of sulfate with sulfuric acid at pH 2.5, fails to re-establish the original chemical structure. Adding sulfate salts of appropriate cations to solutions of the Fe(III) sulfato complex or suspensions of its precipitated polymer in dilute sulfuric acid, result in dissociation of the metastable complex followed by crystallization of ferric ions and sulfate in jarosites. Jarosites and other derivatives of iron precipitation by iron oxidizing thiobacilli, form conspicuous deposits in areas of natural pyrite leaching. The role of iron oxidizing thiobacilli in pyrite leaching, biohydrometallurgy, acid mine drainage, and the cycle of iron and sulfur in nature, has been studied for nearly 50 years. The manifestation of those activities, so widespread on Earth, can be a clue for seeking evidence of life elsewhere.

Intracellular non-crystal magnetosomes are presented in prokaryotes of different taxonomic and physiological groups. Formation of the internal magnetosomes is provoked with some external agents. The situation permits to discuss functions of the magnetosomes as responses to surroundings. A few possible functions are discussed. Hypothesis on oriented motion of bacteria in geomagnetic field suits well data on the linear intracellular distribution of the magnetosomes in some species. An additional hypothesis is oriented attraction of iron-containing compounds to magnetic bacteria. Independently, magnetosomes have a function of the intracellular iron storage. In strong magnetic field, magnetosomes stimulated lysis of bacteria. Sometimes the bacterial lysis was accompanied with production of nanocells.