Twelve meteorites are currently believed to be samples from the Martian surface. Eleven of these meteorites, called the shergottites, nakhlites, and chassignites (or SNC meteorites), have young formation ages (<EQ 1.3 X 10⁹ yr). The twelfth Martian meteorite, ALH84001, is very ancient (4.5 X 10⁹ yr). The differences in formation ages and composition suggest that these twelve meteorites came from at least two and possibly three or more different source craters on Mars. The eleven SNC meteorites are from a young volcanic area, likely the Tharsis Region in the western hemisphere of Mars. Previous studies have identified up to nine possible source craters for these meteorites. The old Martian meteorite, ALH84001, must be from the ancient terrain of Mars, which covers about 40% of the plane primarily in the southern hemisphere. A search through the 42,283-entry Catalog of Large Martian Impact Craters has produced 23 possible source craters, which upon further photogeologic analysis has been reduced to two strong candidates and six runners-up.

Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level. The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient martian biota. We have examined PAHs in the Antarctic shergottite EETA79001, which is also considered to be from Mars, as well as several Antarctic carbonaceous chondrites. We have found that many of the same PAHs detected in the ALH84001 carbonate globules are present in Antarctic carbonaceous chondrites and in both the matrix and carbonate (druse) component of EETA79001. We also investigated PAHs in polar ice and found that carbonate is an effective scavenger of PAHs in ice meltwater. Moreover, the distribution of PAHs in the carbonate extract of Antarctic Allan Hills ice is remarkably similar to that found in both EETA79001 and ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material suggests that this meteorite is contaminated with terrestrial organics probably derived from Antarctic ice meltwater that had percolated through the meteorite. Our data suggests that the PAHs observed in both ALH84001 and EETA79001 are derived from either the exogenous delivery of organics to Mars or extraterrestrial and terrestrial PAHs present in the ice meltwater or, more likely, from a mixture of these sources. It would appear that PAHs are not useful biomarkers in the search for extinct or extant life in Mars.

Because environments on Earth and Mars were quite similar 3.4 - 4 Gyr ago, when life was emerging on Earth, and because terrestrial life emerged very rapidly once conditions permitted, a search for evidence of an extinct martian biota is scientifically credible. However, the criteria to be satisfied for general acceptance of such evidence will be severe. The geochemical, mineralogical and morphological observations recently reported by McKay et al. for the martian meteorite ALH84001 fail to meet those criteria. It is unlikely that study of any known martian meteorites will improve upon this situation. A viable search for evidence of ancient life on Mars will require a sequence of robotic-spacecraft missions, culminating in return of carefully selected samples to Earth. By analogy with the record of early terrestrial life, those samples will be rocks which formed in an aqueous environment and which contain organic matter. Key to successful sample return will be a series of precursor missions capable of, first identifying promising landing sites from orbit, and second identifying promising rocks at such a site. A realistic timeframe for an exobiologically optimized Mars sample return mission is about 2009. Presently unanticipated discoveries may permit an earlier mission, but otherwise an accelerated program would be less likely to succeed scientifically.

Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 - 75 degree(s)C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh (-200 mV to -415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl₂ caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001.

The hypothesis that CI meteorites have an origin on Mars is presented along with supporting data and implications. A Martian origin for the CI will support Martian biogenesis and effect assessments of Martian histories, suggesting Mars and Earth evolved in parallel in both biologic and geologic realms for a long period. The CI containing a Martian pattern of oxygen isotopes and mineralogy indicative of deposition by liquid water. The CI contain no evidence of hypervelocity impact, but contain space-exposed olivine grains and are thus regolith material, indicating their formation under a planetary atmosphere. They contain organic matter similar to that found in Martian meteorites, ALH84001 and EETA79001. A scenario of formation of CI meteorites as being water altered late planetary accretion material is proposed. The 4.5 Gyr age of the CI, matching ALH84001, and their high concentration of organic matter, including possible fossil bacteria, strongly supports the hypothesis of early Martian biogenesis. With CI plus ALH84001 being old, and the SNCs being young, the Martian crustal age dichotomy is now well reflected in Martian meteorite ages. This suggests Mars has a strongly bimodal pattern of crustal ages, either very old or very young with liquid water moving on the planets surface until late in the planets history.

The ability to determine the stable carbon and nitrogen isotope compositions of individual amino acid enantiomers in carbonaceous meteorites can provide insights with respect to their origin(s) and mechanisms of formation. The development of gas chromatography/combustion/isotope ratio mass spectrometry permits such measurements to be made at nanomole to subnanomole levels. Following elution from the gas chromatographic column, the individual compounds are combusted to CO₂ and N₂ which are introduced directly into the source of the isotope ratio mass spectrometer. Our research to date has focused on determining the stable carbon and nitrogen isotope compositions of amino acid enantiomers in unhydrolyzed and hydrolyzed water extracts of the Murchison meteorite (type CM). Our results indicate moderate ((delta) ¹³C) to substantial ((delta) ¹⁵N) enrichments of the individual components relative to terrestrial materials of biological origin. In general, the amino acids are not racemic (L- enantiomer excess). Amino acid distributions and the similarity of (delta) ¹³C and (delta) ¹⁵N values for the D- and L-enantiomers of individual amino acids supports an extraterrestrial origin for this observed optical activity.

A review is presented of the currently available evidence of life in the Precambrian, with special reference to ultrafine morphologies of the size range 0.1 - 3 micrometers . The particles are to be found under high apertures of the light microscope in thin sections of the rock and have been examined in demineralized thick sections under the transmission electron microscope (TEM). They have been chemically analyzed in microprobes and spectrophotometer microscopes. On the basis of such studies, the interaction of microorganisms with the formation of minerals can be traced back to early Archean times, 3800 million years ago. There is no evidence for or against the assumption that some kind of prebiotic evolution took place in the recorded history of the Earth. The origin of life is open to alternative explanations, including extraterrestrial phenomena. More information may be obtained from meteorites. Under high magnifications of the TEM, portions of the carbonaceous matter in the Murchison, Orgueil and Allende meteorites appear to be structured. Particles of various morphology can be distinguished. Microprobe techniques have been applied to confirm that the structures are organic and indigenous to the rock. The origin of the finds is not discussed in the present paper.

The discovery of possible fossils of nanobacteria in a meteorite from Mars is both an exciting development and a considerably challenge for future work. The meteorite bearing the possible fossils, ALH84001, has been on Earth for over ten thousand years, and thus the possibility that the `fossils' are terrestrial contamination must be considered. We suggest that the only way to fully resolve the issue of possible martian life is to study directly- sampled pieces of Mars, either using in situ instrumentation or via sample return. The small size of the possible fossils, and their relatively low abundance in bulk rock samples make in situ analysis difficult and indirect. We suggest that addressing the issue of ancient life on Mars will require sample return, probably assisted by in situ screening by landers/rovers. Our study of ALH84001 confirms the observation of McKay et al. of the existence of `fossils' in ALH84001, and we find that they are highly abundant on all the carbonate nodules we examined. Examination of lunar meteorites and two other martian meteorites, with terrestrial and laboratory histories very similar to that of ALH84001, shows that nano-`fossils' are absent, suggesting that the features in ALH84001 are probably not terrestrial contamination.

Any strategy for investigating whether abiotic and/or biotic organic molecules are present on planetary bodies in the solar system should focus on compounds which are readily synthesized under plausible prebiotic conditions, play an essential role in biochemistry as we know it and have properties such as chirality (handedness) which can be used to distinguish between abiotic vs. biotic origins. Amino acids are one of the few compound classes that fulfill all these requirements. They are synthesized in high yields in prebiotic simulation experiments, are one of the more abundant types of organic compounds present in carbonaceous meteorites and only the L-enantiomers are used in the proteins and enzymes in life on Earth. In contrast, polycylic aromatic hydrocarbons which have recently been detected in some Martian meteorites, have no role in biochemistry on Earth, and their molecular architecture, with the possible exception of the stable isotope composition, cannot be used to determine whether they were produced by biotic or abiotic processes. Recent results indicate that amino acids and their amine decomposition products can be directly isolated from samples using sublimation (450 degree(s) to 750 degree(s)C) under partial vacuum, thus eliminating the use of the aqueous reagents commonly used in the laboratory-based isolation of amino acids. A relatively new technology which shows promise for spacecraft-based amino acid analysis is microchip-based capillary electrophoresis. The actual separation hardware, including buffer reservoirs and derivatization reaction chambers, can be etched onto glass microchips with dimensions on the order of cm. This methodology offers the best potential for a compact, rugged, low-mass instrument package for in situ amino acid analyses during future space missions to Mars, Europa and comets.

The discovery of evidence for biogenic activity and possible microfossils in a Martian meteorite may have initiated a paradigm shift regarding the existence of extraterrestrial microbial life. Terrestrial extremophiles that live in deep granite and hydrothermal vents and nanofossils in volcanic tuffs have altered the premise that microbial life and microfossils are inconsistent with volcanic activity and igneous rocks. Evidence for biogenic activity and microfossils in meteorites can no longer be dismissed solely because the meteorite rock matrix is not sedimentary. Meteorite impact-ejection and comets provide mechanisms for planetary cross-contamination of biogenic chemicals, microfossils, and living microorganisms. Hence, previously dismissed evidence for complex indigenous biochemicals and possible microfossils in carbonaceous chondrites must be re- examined. Many similar, unidentifiable, biological-like microstructures have been found in different carbonaceous chondrites and the prevailing terrestrial contaminant model is considered suspect. This paper reports the discovery of microfossils indigenous to the Murchison meteorite. These forms were found in-situ in freshly broken, interior surfaces of the meteorite. Environmental Scanning Electron Microscope and optical microscopy images indicate that a population of different biological-like forms are represented. Energy Dispersive Spectroscopy reveals these forms have high carbon content overlaying an elemental distribution similar to the matrix. Efforts at identification with terrestrial microfossils and microorganisms were negative. Some forms strongly resemble bodies previously isolated in the Orgueil meteorite and considered microfossils by prior researchers. The Murchison forms are interpreted to represent an indigenous population of the preserved and altered carbonized remains (microfossils) of microorganisms that lived in the parent body of this meteorite at diverse times during the past 4.5 billion years (Gy).

The microstructure and surface microtopography of biogenic carbonate minerals were compared and contrasted with synthetic and natural abiotic carbonates. Bacteria and their by-products on mineral surfaces are imaged in TEM using high-resolution platinum/carbon and gold-decorated replicas. In contrast to SEM, this technique allows imaging of organic and inorganic structures in their original hydrated states and at higher magnification. The material examined so far show different microstructures between bacterial-mediated and inorganic minerals. This suggests that in the absence of preserved microorganisms, the unique microstructure and surface microtopography (biominerals) can be used to recognize biological activities in ancient terrestrial and extraterrestrial rocks.

The Labeled Release (LR) life detection experiment aboard NASA's 1976 Viking Mission reported results which met the established criteria for the detection of living microorganisms on the soil of Mars. However, a variety of reasons led to the consensus of involved scientists that the positive responses at both Lander sites were caused by a chemical agent in the soil and not by microorganisms. In the years since Viking, new information from Mars and Earth has come to bear on this issue. Perhaps most spectacular are the analyses of SNC meteorites ALH84001 and EETA79001. The Viking LR experiment and each of the major chemical theories that have been proposed to explain it are reviewed in the context of these post-Viking developments, together with some Viking data hitherto unapplied to this important issue. Each of the theories attributing the LR results to chemistry is shown to have one or more key defects. It is concluded that the Viking LR experiment detected living microorganisms in the soil of Mars. Recommendations for confirming this conclusion in the near future are given.

There are good reasons to believe that environmental conditions on the martian surface during the first 500 million years (Ma) of its history were dramatically different from those at present. At or before the time at which the early Earth first supported both liquid water and life, before 3850 Ma, Mars apparently underwent erosional processes that strongly suggest a warmer, wetter climate and an operating hydrologic cycle. Martian life may have later become extinct as surface conditions gradually became intolerable, primarily due to atmosphere loss. If it is assumed that life is a 'cosmic imperative', constrained by appropriate environmental conditions conducive to the stability of liquid water, it becomes logical to extend the search for geochemical evidence of past life on the ancient martian surface; a surface that is as old or older than the oldest rocks on Earth. The search fortraces of such life via sample return missions from Mars could be focused on investigating the chemofossil record in ancient water-lain sediments such as paleo-lake beds, fossil hydrothermal fields, and stream channels. Alternatively, martian organisms could have disappeared into the crust, sequestered in discrete P-T microenvironments where liquid water remains stable. Such environments would include deep hydrothermal systems and groundwater aquifers; perhaps such regions continue to support organisms up to the present time.

Techniques for searching for life on Mars will be explored. Work on earth has shown that permafrost and evaporites contain large amounts of bacteria--when this is combined with knowledge of micro-organism hibernation this leads to obvious places in which to search for both extinct and extant life. Great emphasis has been placed on complicated experiments that can only be used at limited locations and in very limited numbers to search for life on Mars, but simple low volume experiments measuring pH, opacity and impedance/conductance could be developed. These would be used to identify potential areas of interest or samples of interest, as well as elucidate Martian geochemistry. The concepts behind these will be explored and examined. The development challenges and Earth based control experiments required will also be outlined. It should be possible to develop relatively cheap experiments that can be used to obtain and sample subsurface materials from a range of locations on Mars.

Martian Salt. Terrestrial halite containing negative crystals which entrapped drops of viscous fluid yielded viable bacteria. The fluid has a Br/Mg ratio which chemist W.T. Holser characterized as a `Permian bittern.' All relevant salt on Mars should be inspected for negative crystals and possible ancient bacterial tenants. Martian Water. Moist soil in the regolith, cooled hydrothermal fluids, sediments of recurrent oceanic water, and related to inferred strand lines, even limited water in future SNC-type meteorites, upper atmosphere liquid water or water vapor, and North Polar liquid water or ice--all liquid water in any form, wherever, should be collected for microbiological analysis. Vent Fauna. Living or fossil thermophiles as trace fossils, or fauna metallicized in relation to sulphide ores. Iron Bacteria. Limonitized magnetite ore (USSR) in thin section showed structures attributed to iron bacteria. Biogenic magnetite, produced by both aerobic and anaerobic bacteria and its significance. Carbonaceous chondrites (non martian) (Ivuna and Orgueil) yielded apparent life forms that could not be attributed to contamination during the given study. Are they extraterrestrial?

A critical step in implementing a strategy to explore for evidence of past or present Martian life and/or prebiotic chemistry is to locate accessible surface outcrops of aqueously-formed sedimentary deposits, especially fine- grained, clay-rich detrital sediments, water-lain volcanic ash deposits, and chemical precipitates which provide especially favorable environments for microbial fossilization. We are presently limited in our site selection efforts by a lack of high spatial resolution remote sensing data at wavelengths that can provide information about surface mineralogy. Globally-distributed compositional data will be obtained at an average spatial resolution of approximately 3 km/pixel by the Thermal Emission Spectrometer instrument launched on the Global Surveyor orbiter in 1996. This will provide a basis for initial targeting of sites for a landed rover missions in 2001 and '03 which will cache samples for potential Earth return in '05. During '05, a sample return vehicle will be sent to one of the previous landed mission sites based on what is learned from those missions during in situ rover investigations. To optimize planning for rover missions to explore for evidence of past life, we need to attain outcrop-scale spatial resolution in the range approximately 100 to 300 m/pixel. This will be required to precisely locate sedimentary deposits of the right mineralogy (i.e. rock types most favorable for preserving a fossil record of past life) at landing sites and be able to reach them with rovers during nominal mission times. The earliest opportunity to obtain high spatial resolution orbital mapping of mineralogy is the 2001 opportunity. This data is needed as early as possible in the '01 mission to influence the landing site selection for the '03 rover mission. Once deposits of exopaleontological interest have been identified from orbit, we must deliver well-equipped, highly mobile science laboratories to the highest priority sites to carry out in situ mineralogical and organic analysis of rocks. To guarantee accessibility to the right samples, we will need to improve (1) landing precision, (2) rover mobility and (3) sample acquisition systems. Ideally, landing precision will match the minimum traverse distances needed for rovers to reach their intended targets within nominal mission times. The landing precision and mobility requirements will vary with each mission, depending on the size of the targeted deposits and terrain trafficability. But some of the highest priority exopaleontological targets (e.g. hydrothermal) are likely to be quite small (few kms²), requiring rover mobility (and equivalent landing precision) in the range of 5 - 10 kms. Under present mission scenarios, rovers in 2001 and '03 will need to screen landing sites for the most promising rocks using in situ analytical methods. Once targeted, rocks will need to be sampled and cached for potential return during the 2005 opportunity. In addition to providing samples for potential Earth return, rovers in '01 and '03 will also gather crucial mineralogical information for ground truthing orbital data. Because sample return payloads are likely to be very small (several hundred grams), sub-sampling of larger rocks will be necessary to ensure that we obtain the most promising materials for return to Earth. In screening rocks to subsample, spectral methods that combine both mineralogical and organic analysis hold the greatest advantages for exopaleontology. However, such analyses will need to be carried out on freshly exposed rock surfaces, requiring rovers that are capable of coring, grinding, and/or breaking rocks. The need for rovers to expose fresh rock surfaces and to efficiently subsample larger rocks will require substantial improvements in sample acquisition and handling systems.

In the initial report by McKay et al. on ALH84001 several lines of evidence were given to suggest the presence of biogenic activity on Mars: (i) the presence of the carbonate globules within fractures and pores of a 4.5 Gy old igneous rock after the primary crystallization event; (ii) formation age of the carbonates is younger than the age of the host igneous rock but older than the carbonate's age; (iii) SEM and TEM images of carbonate globules and assorted features resemble terrestrial biogenic structures and fossilized nanobacteria; (iv) the occurrence of magnetite and iron sulfide particles could have resulted from oxidation and reduction reactions known to be important in terrestrial microbial systems; and (v) presence ofPAHs associated carbonate globules indicating potential indigenous organic molecules. As noted in McKay et al., none of these observations is in itself conclusive proof for the existence of past life on Mars. Although there are alternative explanations for each ofthese phenomena taken individually, when they are considered collectively, particularly in view of their close spatial association, it was concluded that they may represent the first direct evidence for primitive life on early Mars. Since the initial report, additional supporting evidence and contradictory evidence, including alternative inorganic explanations have been presented. The time and temperatures of carbonate formation in ALH84001 continues to be hotly debated. Knott et al. suggests the carbonates were formed at 3.6 Gy, whereas Wadhwa and Lugmair noted the formation may be as late as 1.3 Gy. Turner et al. argue that the 3.6 Gy date is not well defined and additional studies are needed to define the carbonate formation date.

Hydrocarbons like methane and petroleum are common not only on the Earth, but also on most other planetary bodies in our Solar System, as well as interplanetary dust and meteorites. They appear to have been a common constituent of the materials that formed these bodies, and under heat and pressure hydrocarbon fluids would make their way towards the surface. Trace elements in the rocks, including the inert gas helium, would be swept up by such streams, and this would provide the only known explanation for the clear, strong association of hydrocarbons with helium. But all petroleum on Earth also possesses molecules of unquestionably biological origin. If the oil did not derive from biological materials, then only a massive sub-surface microbial life that pervades all oil-bearing regions could account for this. The sub-surface conditions on many other planetary bodies will be quite similar to those on Earth. Therefore I suggested that such life could be widespread in the Solar System, and that one should look for evidence in the first place in the carbonaceous Martian meteorites. The primary food source would be the upwelling hydrocarbons, together with oxygen available from iron and sulfur oxides in the rocks. Carbon dioxide and water will be produced, and the solids that remain will be iron and sulfur in lower oxidation states. The famous Martian meteorite contains indeed low oxidation iron particles and iron sulfide, together with hydrocarbons, a combination characteristic of oil-bearing regions on Earth.

Confirmation of the existence of life on Mars would mean that life has independently evolved on two planets in one solar system and is not a highly improbable event. This would carry the implication that the Universe teems with life -- much of it billions of years older than life on the earth. What is the chance that this life is intelligent? Some prominent evolutionists (e.g., Mayr, Simpson) consider humankind to be a fluke and the prospects for extraterrestrial intelligence to be essentially zero, but their reasoning can be criticized. If the evolution of intelligence is indeed a relatively common occurrence, where do we stand in relation to this cosmic community of intelligent beings? The history of life on the earth combined with numbers from astronomy suggests intriguing answers.

Approximately 11 years ago unexpected transient decreases of Earth's dayglow intensities with spatial dimensions of approximately 50 km in diameter were detected in the first high-resolution global images from a high-altitude orbiting spacecraft, Dynamics Explorer 1. These decreases in dayglow intensities were measured in an ultraviolet spectral window that is very sensitive to absorption by water molecules and clusters along the camera's line-of-sight from the spacecraft to the sunlit atmosphere. These decreases exhibited several features that indicated an extraterrestrial source. Namely (1) preferential motion in the east-to-west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meters, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes as the altitude of the spacecraft decreases. The only viable interpretation of these atmospheric holes to date is the impact of incoming water clouds from small comets that have disrupted in the vicinity of Earth. The startling consequence of this interpretation is an influx of about 20 small comets each minute into our atmosphere, each with a mass of tens of tons. These measurements and interpretation inspired a heated debate which resulted in dismissing the small comets because the observations were generally obtained at the imager's threshold. A new ultraviolet imager with more than 100 times the resolution of the Dynamics Explorer-1 camera has been recently flown on the Polar spacecraft. These images from the Polar camera confirm the existence of the small comets. A mission to further investigate the composition and dynamics of these small comets is suggested.

Ever since the first proposal that tidal heating of Europa by Jupiter might lead to liquid water oceans below Europa's ice cover, scientists have speculated over the exobiological implications of such an ocean. Liquid water is thought to be an essential ingredient for life, so the existence of a second water ocean in the Solar System would be of paramount importance in any search for life beyond Earth. We present here a Discovery-class mission concept (Europa Ocean Discovery) to determine the existence of a liquid water ocean on Europa and to characterize Europa's surface structure. The technical goal of the Europa Ocean Discovery mission is to study Europa with an orbiting spacecraft. This goal is challenging but entirely feasible within the Discovery envelope. There are four key challenges: entering Europan orbit, generating power, surviving long enough in the radiation environment to return valuable science, and completing the mission within the Discovery program's constraints on launch vehicle (Delta II or smaller) and budget (approximately $DOL250M plus launch). Europa Ocean Discovery will carry four scientific instruments to study Europa: (1) an ice-penetrating radar sounder to probe tens of kilometers below Europa's surface; (2) a laser altimeter, to determine the height and phase of Europa's time-varying tidal bulge; (3) an X-band transponder to determine Europa's gravity field; and (4) a solid-state optical imager. These instruments will provide important information about Europa's surface, subsurface, and will provide definitive evidence about the existence of a Europan ocean.

The present work was stimulated by the possibility of designing an advanced lander mission that may melt through the ice layer above the Europan ocean, in order to deploy a tethered submersible. We devote our attention to the determination of the degree of evolution of the biota, and the determination of the Europan environments that should be probed. As the most likely microorganisms in the Europa ocean are archaebacteria, we argue that evolution should have occurred, as hydrothermal vents are assumed to be present at the bottom of the ocean and such environments are known not to be refuges against evolution. We argue that a factor in interpreting the lack of uniformity in surface brightness and color of the Europan surface may be the presence of microorganisms. This hypothesis can be tested by spectroscopic search for not only the precursors of biomolecules (as has already been confirmed by the Galileo Mission in the case of Ganymede and Callisto), but a spectroscopic search should also be conducted for the biomolecules themselves, such as nucleotides, aminoacids, lipids and polysaccharides. The submersible seems to be the most appropriate means for a program in the search for extraterrestrial eukaryotes (SETE), but we also discuss SETE in the context of another proposal.

Astronomical spectra over a wide range of wavelengths is reviewed and compared with predictions from organic models of interstellar and cometary grains. The data requires the widespread occurrence of functional groups involving H,O,C,N in the form of complex structures in the proportions that characterize biomaterial. We argue for the widespread occurrence of a microbiological system on a galaxy-wide scale.

A variety of means can be employed to search for extraterrestrial life. Large-scale extraterrestrials are reasonably expected to have developed intelligence (since intelligence is selectively advantageous) and technology (since technology also provides advantages). In the expectation/hope that more advanced extraterrestrials will be sending an announcement signal to help us make contact and share in our galactic heritage, more than 30 radio searches have been carried out over the last 40 years. Current searches are up to 4 orders of magnitude more sensitive and cover up to 10⁸ more bandpass than the original searches. An overview of the rationale behind these searches and the current status of this work is provided.

More than 112 interstellar molecular species have been reported to date. Small interstellar molecules and large interstellar molecules with a low degree of saturation (low hydrogen count) can be formed in quiescent gas clouds or in shock fronts by gas-phase chemical reactions, such as ion- molecule reactions and neutral-neutral reactions. Because these gas-phase species are found in spatially extended clouds, they have dominated most of the past single-element telescope studies of extended interstellar molecular clouds. Now, with the advent of radio interferometric arrays that operate at millimeter wavelengths with high spatial resolution, the study of a rich dust-phase chemistry around small hot molecular cloud cores has become possible. These small cloud cores, less than 0.1 parsec in diameter, form the type of dusty environment that contains presolar nebulae contracting under gravity before the onset of fusion; they contain large, complex, interstellar molecules with a high degree of saturation that are also of some biological interest: acetone, ethyl cyanide, ethanol, acetic acid, and probably the smallest amino acid, glycine. These molecules cannot be formed easily by gas-phase reactions alone; consequently, theories of solid state chemical reactions on grain surface ice mantles are often invoked to form these large molecules and evaporation is proposed as the mechanism that drives them into the gas phase. Hence, high resolution millimeter-wavelength arrays can spectroscopically sample the composition of evaporated presolar material--the material that eventually may form the basis for a type of prebiotic organic chemistry similar to that found on the early Earth.

A summary follows of our experiences and techniques used in the analysis of samples from Apollo Missions 11 to 17. The studies were conducted at the Ames Research Center, Moffett Field, CA, the University of Missouri, Columbia, MO, and the University of Maryland, College Park, MD, 1969 - 1974. Our search was directed to water-extractable compounds with emphasis on amino acids. Gas chromatography, ion-exchange chromatography and gas chromatography combined with mass spectrometry were used for the analysis. It is our conclusion that amino acids are not present in the lunar regolith above the background levels of our investigation (ca. 1 - 3 ng/g). The scientific debate has become heated that primitive life existed on Mars 3.6 billion years ago as reported by the NASA-Stanford team led to David McKay. Mars is destined to receive humans early in the 21st Century, preceded by many international missions to Space Station Freedom and robotic missions to the Moon and Mars. First, we must `learn to live in space'. The Moon presents a base that provides the opportunities and challenges to assemble the international interdisciplinary intellectual scientific teams and partners with many disciplines to make the next step before human exploration of Mars and the search for evidence in Martian soil and samples returned to Earth laboratories. Our experiences learned in Moon analysis will be useful in Mars exploration and returned sample study. Sensitivity at the nanogram/gram level and selectivity of analysis are highly essential. As these figures show contamination of samples is a most serious problem. However with the use of ultraclean techniques in a 100 clean room contamination can be avoided. Our speck of dust, a tiny fragment of cigarette smoke, a particle of dandruff, a droplet of saliva, all can make your results questionable. In addition, the extraction of life molecules as amino acids from the Lunar samples was a difficult process and I am sure the same difficulties exist with handling and removing the very low levels of amino acids from Mars meteorites and returned samples.

The complete 1.66 megabase pair genome sequence of the extreme thermophilic, autotrophic archaeon Methanococcus jannaschii has been determined by whole-genome random sequencing. Out of a total of 1751 predicted protein coding genes, only 44% could be assigned a putative cellular role with high confidence, and only 57% are homologous to genes known in other organisms. For 43% of the M. jannaschii genes no related gene is known in any other organism. Although the majority of the genes related to energy production, cell division, and metabolism in M. jannaschii are most similar to those found in Bacteria, most of the genes involved in the processing of information (transcription, translation, and replication) are more similar to their counterparts in Eukaryotes. The analysis of the M. jannaschii genome holds not only clues for the basis of life under extreme conditions, but the comparison of its information content with that of the genomes from other model organisms, like the bacterium Escherichia coli and the eukaryote Saccharomyces cerevisiae, also provides clues for the reconstruction of the history of many gene families and for the history of life on earth.

Halobacteria cultured from salt deposits as old as 200 m.y. are assumed to be dormant halobacteria entombed in the brine inclusions that formed during deposition of the salt crystals. Hypersaline lakes may have also existed on early Mars. If so, evaporite minerals containing frozen brine inclusions may occur on the surface of Mars today. Analyses of samples of recently-deposited salt from Laguna Grande de la Sal in New Mexico revealed the presence of viable halobacteria. 16S rDNA from archae and eubacteria was also detected by polymerase chain reaction (PCR) amplification of directly-extracted DNA from Laguna Grande de la Sal sal. In contrast, no halophilic bacteria were cultured from 200 my polyhalite from the Salado Formation in New Mexico nor was archaea 16S rDNA detected by PCR amplification of DNA extracts from salt. A combination of microbiological, molecular, and geochemical approaches are being used to probe bedded salt deposits for evidence of microbial entrapment in primary fluid inclusions. A chronosequence of bedded salts from Death Valley, California that range in age from 0 to 200 kyr is the subject of current investigations to constrain the length of time that viable halophilic bacteria and associated macromolecules can be detected in bedded salts.

A borehole drilled to a final depth of 6779 m in granitic rock in Gravberg, Sweden, was sampled and examined for the presence and activity of anaerobic bacteria. The application of anaerobic enrichment and isolation techniques resulted in pure cultures of various fermenting bacteria. Growth in enrichment cultures was observed only in those cultures inoculated from water samples from a depth of 3500 m. Pure cultures of anaerobic, fermenting bacteria were obtained with the following substrates: glucose, starch, xylane, ethanol, and lactate. All isolated bacteria were so far undiscribed bacteria by means of their physiological properties. One strain of the glucose fermenting bacteria was further characterized concerning its phylogenetic position and was found to be closest related to Clostridium thermohydrosulfuricum. However, by means of its characteristic metabolism, it was clearly separated from C. thermohydrosulfuricum. No sulfate-reducing or methanogenic bacteria were found in any of the samples. Fermentative bacteria growing in the presence of hematite often reduced the iron and induced the formation and deposition of insoluble iron sulfides.

Extreme environments, such as aqueous, high temperature, mineralizing systems (thermal springs) are the focus of the search for evidence of life on early Earth or on Mars. Mineral deposition from saturated waters potentially entombs these organisms complicating hydrological control of the fossilization process. Near-surface and subsurface hydrology of these systems is governed by the porosity and continuity of pore spaces in microbial mats and associated sinter deposits. Herein we examine the evolution of pore space in microbial mats with emphasis on the relationship between pore size and geometry, and silica deposition. Microbial mats living in the outflow channels of silica-rich thermal springs in Yellowstone National Park, WY, and Steamboat Springs, NV are best preserved under conditions of intermittent inundation and drying and/or cooling. This leads to periodic deposition of silica initially as a coating on the cells and eventually as an infilling in the cells. As a consequence, pore spaces between microbial filaments retain characteristic configurations and are filled with silica crystals of different size and morphology than that of the coatings or fillings. The nature of the pore-filling silica is controlled by the temperature and chemistry of the water flowing through the sinter mound and is indicative of the environment of preservations.

Recent investigations have identified microorganisms in various crustal environments to 2800 meters below the surface (mbls.). Relatively few deep samples of the continued crust (> 800 mbls.) have been collected for microbiological analyses, however, because coring is technically difficult and expensive. The gold mines into the 2.9 Ga Witwatersand Supergroup in South Africa may provide an alternative means of studying microbial communities at depths up to 3500 meters. Uranium-rich, Au-bearing, carbonaceous rock and water from a gallery borehole at a mined depth of 3200 mbls, and an ambient temperature of 50 degree(s)C were collected for microbial analyses. Measures were taken to avoid contamination during mining and sampling. Samples were shipped to the USA in sterile, anaerobic canisters on ice, processed under sterile anaerobic conditions and distributed to participating labs. Microscopic observations revealed the presence of intact cells including filamentous microorganisms. Phospholipid fatty acid and DNA analyses indicated that the samples contain cyanobacteria, sulfate-reducing bacteria and iron- reducing bacteria (IRB). The water sample yielded a strain of Thermus (IRB-SA) that is the first reported Thermus to reduce Fe(III) and the first facultative, thermophilic Fe(III) reducer.

Evidence is accumulating to show that the Earth's biosphere extends underground into deep igneous rock formations. In certain formulations, abiotic energy-yielding reactions between reduced rocks and groundwater provide a potential for in situ primary production by anaerobic microorganisms-- thus obviating any dependence on a surface ecosystem. Conceivably, such ecosystems could exist in the subsurface of other planets in the solar system. The main requirements are water, ferrous silicate minerals, carbon dioxide, and nitrogen. Unfortunately, observation of the subsurface is difficult. For example, current estimates suggest that the hydrosphere on Mars might be more than 2 km below the surface. Living SLMEs might be detected through conduits to the subsurface, such as wells, springs, or seeps in deep canyon walls. Signals produced by SLMEs might include cells, metabolic products (such as reduced gases) and their isotope ratios, and isotope ratios in residual substrates. Rocks in which now-defunct SLMEs once existed might be more accessible if they are brought to the surface by rock cycle processes. Signals of extinct SLME remnants have not yet been investigated, but might include microfossils, certain secondary mineralization patterns, and isotope ratios of secondary materials. Examples of both extant and extinct SLMEs have been identified on Earth, and are available for study and experimentation.

Biogeochemical modeling of groundwater flow and nutrient flux in subsurface environments indicates that inhabitant microorganisms experience severe nutrient limitation. Using laboratory and field methods, we have been testing starvation survival in subsurface microorganisms. In microcosm experiments, we have shown that strains of two commonly isolated subsurface genera, Arthrobacter and Pseudomonas, are able to maintain viability in low-nutrient, natural subsurface sediments for over one year. These non- spore-forming bacteria undergo rapid initial miniaturization followed by a stabilization of cell size. Membrane lipid phospholipid fatty acid (PLFA) profiles of the Pseudomonas are consistent with adaptation to nutrient stress; Arthrobacter apparently responds to nutrient deprivation without altering membrane PLFAs. To test survivability of microorganisms over a geologic time scale, we characterized microbial communities in a sequence of unsaturated sediments ranging in age from modern to > 780,000 years. Sediments were relatively uniform silts in eastern Washington State. Porewater ages at depth (measured by the chloride mass- balance approach) were as old as 3,600 years. Microbial abundance, biomass, and activities (measured by direct counts, culture counts, total PLFAs, and radiorespirometry) declined with sediment age. The pattern is consistent with laboratory microcosm studies of microbial survival: rapid short-term change followed by long-term survival of a proportion of cells. Even the oldest sediments evinced a small but viable microbial community. Microbial survival appeared to be a function of sediment age. Porewater age appeared to influence the makeup of surviving communities, as indicated by PLFA profiles. Sites with different porewater recharge rates and patterns of Pleistocene flooding had different communities. These and other studies provide evidence that microorganisms can survive nutrient limitation for geologic time periods.

The surfaces of bacteria are highly interactive with their environment. Whether the bacterium is gram-negative or gram- positive, most surfaces are charged at neutral pH because of the ionization of the reactive chemical groups which stud them. Since prokaryotes have a high surface area-to-volume ratio, this can have surprising ramifications. For example, many bacteria can concentrate dilute environmental metals and silicates on their surfaces and initiate the development of fine-grained minerals. In natural environments, it is not unusual to find such bacteria closely associated with the minerals which they have helped develop. Since bacteria usually prefer to grow as biofilms on macroscopic surfaces in most natural ecosystems (supposedly to take advances of the nutrient concentrative effect of the interface), they can form films micrometers -to-mm-thick. Using a gram-negative bacterial model, we have found that lipopolysaccharide (a surface component) is important in the initial attachment of the bacterium to the substratum. This macromolecule is also important for the entrapment of metals and the instigation of mineral development. Eventually, biofilms become so mineralized that the shape and form of the constituent bacteria are preserved and embedded in the rock as it forms. These mineralized bacteria are called `microfossils' and it is possible that the same set of circumstances could have preserved small lifeforms on Mars given similar environmental conditions.

Deep unsaturated sediments with very low levels of sediment- associated nutrients and extremely low levels of vertical movement of moisture (i.e., recharge) were studied as a model extreme environment to better understand microbial survival over geologic time periods and the resulting spatial distribution of viable microorganisms. Chloride mass balance measurements indicate that the study site has received an average annual recharge of 15 micrometers since the last Pleistocene flood approximately 13,000 years ago. Viable biomass as determined by measurement of phospholipid fatty acid in 75 g samples was approximately 10⁴ cells/g sediment. However, highly sensitive microbial activity assays failed to detect microbial activity in > 60% of 10 g samples. Microbial activity was not detected in 29% of replicate 10 g samples in the presence of nutrients for 244 days, indicating that viable microorganisms are spatially discontinuous. In separate experiments, microbial activity was not detected in 0.1 g or 1 g samples but was encountered in 37% of the 10 g samples and in 75% of the 100 g samples. These results indicate that viable microorganisms exist in `hotspots' separated by extensive regions of excluding conditions. In addition, the results suggest that if extremely low nutrient flux conditions exist at target extraterrestrial locations, successful recovery of viable microorganisms may require acquisition of many, or large, samples.

The effect of biological fractionation of carbon and sulfur isotopes is described now for many microbial processes. Stable isotope composition of carbon and sulfur gases and minerals, produced by microorganisms depends on isotope composition of initial substrates, part of substrate consumed by microorganisms and rate of microbial metabolism.

Nannobacteria are minute spherical to worm-shaped cells (diameter 0.03 to 0.2 micrometers ) that participate in the formation of carbonates, clays, and other minerals on Earth. The supposed nannobacterial objects found by the National Aeronautics and Space Administration in the Martian meteorite can be exactly duplicated as to morphology and size by earthly examples. Grapelike colonies of 0.05-micrometers carbon balls in the Allende meteorite also resemble nannobacterial colonies in south Italian volcanic clays.

Nanobacteria are the first mineral forming bacteria isolated from blood and blood products. They are coccoid cell-walled organisms with a size of 0.08 - 0.5 micrometers in EM, occure in clusters, produce a biofilm containing carbonate or hydroxyl apatite, and are highly resistant to heat, gamma-irradiation and antibiotics. Their growth rate is about one hundredth that of ordinary bacteria and they divide via several mechanisms. Taq polymerase was able to use their nontraditional nucleic acid as a template. 16S rRNA gene sequence results positioned them into the alpha-2 subgroup of Proteobacteria. Nanobacteria are smallest cell-walled bacteria since they can pass through 0.07 micrometers pores. In low-serum cultures, they form even smaller elementary particles or tubular units. How can blood be infected with such slow growing, heat and radio-resistant bacteria? The answer may lie in their phylogeny: alpha-2 subgroup has organisms from soil exposed to radiation and heat, that can penetrate into eukaryotic cells. Nanobacteria grow so slowly that they require a niche `cleaned' with heat, radiation or immunodefence. For survival they cloak themselves in apatite, a normal constituent of mammalian body. This may link nanobacteria to nannobacteria discovered from sedimentary rocks by Dr. Folk. Both have similar size, size variation, clustering and mineral deposits. They may resemble the probable ancient bacterial fossils in the Martian meteorite ALH84001.

Nanobacteria, novel sterile-filterable coccoid bacteria inhabiting mammalian blood and blood products, have different growth phases depending on the culture conditions. These minute organisms produce biogenic apatite as a part of their envelope. This becomes thicker as the cultures age, rendering them visible in microscopy and resistant to harsh conditions. Mineral deposits were not formed without live nanobacteria. Apatite formation was faster and more voluminous in serum-free (SF) medium, and within a week, several micrometer thick `castles' formed around each nanobacteria. These formations were firmly attached to the culture plates. Nanobacteria multiplied inside these thick layers by turning into D-shaped forms 2 - 3 micrometers in size. After a longer culture period, tens of them could be observed inside a common stony shelter. The apatite shelters had a hollow interior compartment occupied by the organisms as evidenced by SEM and TEM. Supplementing the culture medium with a milk growth-factor product, caused the castles to grow bigger by budding. These formations finally lost their mineral layer, and released typical small coccoid nanobacteria. When SF cultures were supplemented with sterile serum, mobile D-shaped nanobacteria together with small `elementary particles' 50 - 100 nm in size were found. Negative results in standard sterility testing, positivity in immunofluorescence staining and ELISA tests with nanobacteria-specific monoclonal antibodies, and 98% identity of 16S rRNA gene sequences proved that all of these unique creates are nanobacterial growth phases.

Nanobacteria are minute bacteria recently isolated from mammalian blood. They encapsulate themselves with apatite mineral. Cultured nanobacteria were radiolabeled with ^99mTc, using a method which has been previously used for labeling red blood cells with ^99mTc, and in vivo distribution of nanobacteria was followed with Single Photon Emission Computed Tomography (SPECT) imaging. The labeling yield was over 30%. Two rabbits were studied using dynamic planar imaging performed in the AP-position immediately after injection. Serial SPECT scans were acquired up to 24 h and one planar image was taken at 45 h. A control study was performed administering a similar dose of [^99mTc] labeled albumin nanocolloids. Regional nanobacteria-to- nanocolloid ratios were calculated along with time and tissues (45 h) were analyzed for radioactivity and for nanobacteria. The main finding was that radiolabeled nanobacteria remained intact and showed a tissue specific distribution with a high accumulation in the kidneys and also in urine. Spleen, stomach, heart and intestine also showed increased uptake. Excretion into urine started 10 - 15 min after injection. These were live nanobacteria in the urine, which had better capabilities to penetrate into cells in vitro. The nanobacteria accessed the urine via tubular cells since nanobacteria were found in their cytoplasm and tubular surfaces. The results suggest that nanobacteria utilize endocytic transport of tubular cells and may be involved in the pathogenesis of mineral formation in mammalian kidney stones.

Retrieval of viable bacteria from fossil material dating from the Oligocene back to the Miocene opens the opportunity to study the evolution of prokaryotes through the evolution of their DNA, their physiology, and their ecology. This unique system in which ancient organisms and their genes may be compared directly, rather than by inference, with modern homologues is without precedent. Clearly, however, confirmation of the fossil origin of such isolates must be made in a manner that would allay reasonable skepticism. Present approaches of verification of authenticity of fossil DNA are either arbitrary or potentially unconvincing, because of their dependence on imprecise methodological observations. New approaches for verification must be developed at the same time as further research in fossil bacterial isolation and characterization proceeds. The discovery that viable bacterial spores from fossil materials opens the way to direct assessment of the evolution of complex biochemical systems in prokaryotic systems and to explore mechanisms for long term survival of microorganisms.

From the first noteworthy investigations of possible extraterrestrial organisms, many subsequent studies have generated heated controversies about extraterrestrial life even until today. Many scientists and visionaries presaged our remarkable, growing paradigm shift resulting from the indomitable idea that the proven scientific fact of extraterrestrial life is an inevitability. It is likely that most `revived' ancient microorganisms would not be very similar to any related modern microorganisms, because of the great time span available for the latter to diversity from the former. On the other hand, it is known that some complex brachiopod species of the common genus, Lingula, have survived for over a half billion years with `little evident change' since Cambrian times. Indirect evidence against modern contamination is offered by the fact that most `revived' bacteria from older terrestrial rocks are unlike any known modern species, and many microfossil-like structures (alleged by skeptics to be contaminants) in carbonaceous meteorites are yet to be confirmed as terrestrial in origin.

The currently available sedimentary carbon isotope record goes back to 3.85 Ga and conveys a remarkably consistent isotopic signal of biological carbon fixation based on the bias for light carbon (¹²C) exercised by common photosynthetic pathways. This holds particularly for the time segment < 3.5 Ga, whereas the older (Isua) record is blurred by a metamorphic overprint. In spite of the marked impairment of the oldest evidence by isotopic reequilibration between organic and carbonate carbon in the wake of the amphibolite-grade metamorphism suffered by the host rock, a coagent case can be built for the emergence of (photo)autotrophic carbon fixation and the start of a biogeochemical carbon cycle as from at least 3.85 Ga ago. This would imply that microbial (prokaryotic) ecosystems had been prolific on the Archaean Earth not long after the formation of the planet.

Cold adapted viable paleomicroorganisms, the only known organisms, survive `in situ' within permafrost at subzero temperatures over geological time and upon thawing resume the activities. Because the cryosphere existence is a common phenomenon in space, the terrestrial permafrost environment inhabited by microbes and their metabolically end products can be considered as a model of conditions of the other planets. Ancient microbial communities within the Earth permafrost provide a range of analogies for possible extraterrestrial ecosystems, which might be found at permafrost depths on other planets. The main econiches where the microorganisms may survive are the unfrozen water films enveloping soil particles and functions as a cryoprotector. This type of rigidly associated `liquid' water has not been sublimated and may present in extraterrestrial cryosphere as a life indicator.

Several species of antarctic sea ice diatoms have been found to release ice-active substances (IAS). At natural concentrations, they produce dense pitting on ice crystal surfaces at temperatures slightly below the freezing point, without significantly affecting the freezing point. This phenomenon appears to be associated with cold-adapted species as it has not been found in temperature fresh water and marine diatoms. IASs have been found in several species of sea ice diatoms, including both attached and unattached species. The ice-active substances have been found both in ice platelet water as well as in the solid congelation ice in McMurdo Sound in early summer, and in newly formed ice in winter in the Weddell and Bellinghausen seas. An IAS- producing species (Amphiprora) was cultured in the laboratory and produced noticeable increases in IAS activity. The IAS is retained by dialysis tubing and appears to be proteinaceous, as it is inactivated by proteases and heat. Further attempts to purify and characterize the IAS are in progress. The role of the IAS is unknown. Possible roles involving attachment of diatoms to ice and modification of the optical properties of ice are being considered.

One of the more likely places in the solar system for the existence of extraterrestrial life forms is the Jovian moon Europa. It has been postulated that a volcanically-heated ocean is likely to exist underneath Europa's icy surface. If a detailed remote-sensing reconnaissance of Europa determines that an ocean does exist under the ice, then in- situ measurements will be needed to directly explore the Europan ocean and the ice that lies above it. In order to make quantitative measurements of the Europan environment, a lander spacecraft capable of penetrating the surface ice layer by melting through it is proposed. This vehicle, dubbed a `Cryobot', will be designed to carry a small deployable submersible (a `Hydrobot') equipped with a complement of instruments. The design of an instrument package to search for life across the wide range of thermal and pressure environments expected on Europa, the issues in sample handling, and long-term reliability for a potential multi-year transit through the ice all present difficult design issues. Opportunities for performing investigations of deep, submerged Antarctic lakes on Earth are described which would test the Cryobot/Hydrobot system while collecting intrinsically valuable terrestrial science data.

In water-in-oil microemulsions, microdroplets of water, surrounded by a layer of surfactant molecules (reversed micelles), are dispersed in an organic solvent. Various microorganisms (unicellular algae and cyanobacteria) and isolated enzymes were dispersed in microemulsions without loss of biological activity. Each biological system needed a defined quantity of water in the microemulsion for maximum activity. Under optimum conditions, microbial enzymes for various sources (hydrogenases, dehydrogenases) exhibited, besides ten-fold increase in specific activity, a temperature optimum up to 16 degree(s)C higher as compared to aqueous solutions. These experimental findings, together with theoretical considerations, imply that water structure inside reversed micelles is very different from free water, but similar to water in narrow compartments with polar or ionic surfaces. These compartments may represent a model system for environments, where (liquid) water is not available in bulk amounts, but embedded in an anhydrous matrix.

Microorganisms are able to exist in extreme environments, where they often form biofilms. We are investigating an iron metabolizing biofilm consortium derived from groundwater draining the Canadian Shield. This was first discovered in the Underground Research Laboratory of Atomic Energy of Canada Ltd., where its influence on the management of nuclear fuel waste was examined. Incubations have shown that the microbial consortium contains different morphological forms. Ultramicrobacteria, 0.3 micrometers diameter cocci, are dominant on magnetite surfaces, which they are able to transform rapidly to hematite. Larger rods, 1.0 micrometers long, aggregate on silicon minerals containing little iron. Carbon is limited in these natural groundwaters so that iron is utilized as an alternative energy source. The cell surface of the organisms and the extracellular polymers of the biofilm are both negatively-charged allowing metal cations to be quickly bound by physicochemical sorption, thus providing nucleation sites for mineralization within the boundaries. The biofilm consortium is able to mediate a wide range of iron reactions. Aerobically a ferric gel is precipitated throughout the biofilm slime, which alters first to ferrihydrite and later to hematite. When anaerobic fermentation produces a reducing environment the iron is converted to the ferrous state which may then be precipitated as ferrous hydroxide, vivianite or siderite. Since iron is widespread in the natural environment, these reactions could have important geochemical implications.

Total community DNA and RNA were extracted from a deep (188 m), saturated, mesophilic (17 degree(s)C), low biomass (10⁴ cells g^-1) subsurface paleosol. 16S rDNA was amplified by PCR using universal eubacterial or archaeal primers and cloned. Cloned 16S rDNA fragments were sequenced and subjected to phylogenetic analysis. A novel clade of Crenarchaea were discovered which are most closely related to a single clone recovered from an Fe-S hot spring (80 degree(s)C). Novel Bacterial sequences were also found which branch deeply in the universal phylogenetic tree in association with Chloroflexus, Deinococcus, and Thermus. Total RNA analysis suggested that the novel Crenarchaea were active in this environment. Geological and hydrologic properties of the sediment indicate that microbial and nutrient transport between individual strata are restricted, and are consistent with chemolithoautotrophic metabolisms of cultured Crenarchaea involving the H₂/SO₄ electron donor/acceptor couple. The physical properties of the surrounding lithologies suggest that these novel microorganisms are descendants of the microbial communities originally deposited with the sediment ca. 6 - 8 Mya. Identification of these novel, active microorganisms in an oligotrophic, hydrologically isolated subsurface system provides an opportunity and species-specific nucleic acid sequences and probes necessary to study long-term microbial survival in terrestrial subsurface environments.

Interstellar dust grains have mantles of prebiotic organic molecules. A large fraction of the clouds of interstellar dust grains pass close enough to neutron stars for the circularly polarized ultraviolet radiation to produce a 10% or higher enantiomeric excess (e.e.) in the organic grain mantles. The time between such close passages is about ten times larger than the average lifetime of the molecular clouds so that most prestellar and protostellar clouds contain predominantly left or right handed prebiotic molecules; i.e., those clouds that collapse to form stars have probably passed by only one neutron star. Comets as agglomerated interstellar dust preserve the initial enantiomeric excess at least as well as meteorites which have been recently shown to have an e.e. of about 10%. Even if only 0.1% of the comet material survives as small comet dust particles that preserve their prebiotic molecules, there could be approximately 10²⁵ chances for life to originate from one of these if it lands in water because of the special structure as well as composition of fluffy comet dust.

Homochirality is a characteristic signature of life or at the very least pre-biotic chemistry, and we explain how biotic and pre-biotic homochirality can be distinguished. We discuss the implications of the recent discovery of an enantiomeric excess in the Murchison meteorite. We describe how a combination of gas-chromatography and polarimetry could be used to detect life on mars, and introduce new vistas for space polarimetry in our proposed Search for EXtra-SOlar Homochirality (SEXSOH).