Antarctic Dry Valleys and indigenous weathering in Mars meteorites: Implications for water and life on Mars

The Dry Valleys of Antarctica are an excellent analog of the environment at the surface of Mars. Soil formation histories involving slow processes of sublimation and migration of water-soluble ions in polar desert environments are characteristic of both Mars and the Dry Valleys. At the present time, the environment in the Dry Valleys is probably the most similar to that in the mid-latitudes on Mars although similar conditions may be found in areas of the polar regions during their respective Mars summers. It is thought that Mars is currently in an interglacial period, and that subsurface water ice is sublimating poleward. Because the Mars sublimation zones seem to be the most similar to the Antarctic Dry Valleys, the Dry Valleys-type Mars climate is migrating towards the poles. Mars has likely undergone drastic obliquity changes, which means that the Dry Valleys analog to Mars may be valid for large parts of Mars, including the polar regions, at different times in geologic history. Dry Valleys soils contain traces of silicate alteration products and secondary salts much like those found in Mars meteorites. A martian origin for some of the meteorite secondary phases has been verified previously; it can be based on the presence of shock effects and other features which could not have formed after the rocks were ejected from Mars, or demonstrable modification of a feature by the passage of the meteorite through Earth's atmosphere (proving the feature to be pre-terrestrial). The martian weathering products provide critical information for deciphering the near-surface history of Mars. Definite martian secondary phases include Ca-carbonate, Ca-sulfate, and Mg-sulfate. These salts are also found in soils from the Dry Valleys of Antarctica. Results of earlier Wright Valley work are consistent with what is now known about Mars based on meteorite and orbital data. Results from recent and current Mars missions support this inference. Aqueous processes are active even in permanently frozen Antarctic Dry Valleys soils, and similar processes are probably also occurring on Mars today, especially at the mid-latitudes. Both weathering products and life in Dry Valleys soils are distributed heterogeneously. Such variations should be taken into account in future studies of martian soils and also in the search for possible life on Mars.     

Meridiani Planum hematite deposit and the search for evidence of life on Mars—iron mineralization of microorganisms in rock varnish

The extensive hematite deposit in Meridiani Planum was selected as the landing site for the Mars Exploration Rover Opportunity because the site may have been favorable to the preservation of evidence of possible prebiotic or biotic processes. One of the proposed mechanisms for formation of this deposit involves surface weathering and coatings, exemplified on Earth by rock varnish. Microbial life, including microcolonial fungi and bacteria, is documented in rock varnish matrices from the southwestern United States and Australia. Limited evidence of this life is preserved as cells and cell molds mineralized by iron oxides and hydroxides, as well as by manganese oxides. Such mineralization of microbial cells has previously been demonstrated experimentally and documented in banded iron formations, hot spring deposits, and ferricrete soils. These types of deposits are examples of the four “water-rock interaction” scenarios proposed for formation of the hematite deposit on Mars. The instrument suite on Opportunity has the capability to distinguish among these proposed formation scenarios and, possibly, to detect traces that are suggestive of preserved martian microbiota. However, the confirmation of microfossils or preserved biosignatures will likely require the return of samples to terrestrial laboratories.     

Distribution, ,movement,and evolution of the volatile elements in the lunar regolith

The abundances and distributions of carbon, nitrogen, and sulfur in lunar soils are reviewed. Carbon and nitrogen have a predominantly extra-lunar origin in lunar soils and breccias, while sulfur is mostly indigeneous to the Moon. The lunar processes which effect the movement, distribution, and evolution of carbon, nitrogen, and sulfur, along with the volatile alkali elements sodium, potassium, and rubidium during regolith processes are discussed. Possible mechanisms which may result in the addition to or loss from the Moon of these volatile elements are considered.     

Homochirality as the signature of life: the SETH Cigar

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.     

Trace elements and the panspermia hypotheses

The modal concentrations of elements in four representative classes of organisms, namely bacteria, fungi, plants, and land animals, are compared with the concentrations of the elements in sea water. A strong correlation is found between these concentrations, and this correlation reduces to an expected linear concentration law when only “trace” elements are considered. Deviations from strict linearity are shown to arise from the chemical natures of the elements Apart from suggesting an oceanic genesis for terrestrial life, the data are strongly against a nonterrestrial origin of life as proposed by the panspermia hypotheses.     

Volcaniclastic habitats for early life on Earth and Mars: A case study from ∼3.5 Ga-old rocks from the Pilbara, Australia

Within the context of present and future in situ missions to Mars to investigate its habitability and to search for traces of life, we studied the habitability and traces of past life in ∼3.5 Ga-old volcanic sands deposited in littoral environments an analogue to Noachian environments on Mars. The environmental conditions on Noachian Mars (4.1-3.7 Ga) and the Early Archaean (4.0-3.3 Ga) Earth were, in many respects, similar: presence of liquid water, dense CO₂ atmosphere, availability of carbon and bio-essential elements, and availability of energy. For this reason, information contained in Early Archaean terrestrial rocks concerning habitable conditions (on a microbial scale) and traces of past life are of relevance in defining strategies to be used to identify past habitats and past life on Mars.One such example is the 3.446 Ga-old Kitty’s Gap Chert in the Pilbara Craton, NW. Australia. This formation consists of volcanic sediments deposited in a coastal mudflat environment and is thus a relevant analogue for sediments deposited in shallow water environments on Noachian Mars. Two main types of habitat are represented, a volcanic (lithic) habitat and planar stabilized sediment surfaces in sunlit shallow waters. The sediments hosted small (<1 μm in size) microorganisms that formed colonies on volcanic particle surfaces and in pore waters within the volcanic sediments, as well as biofilms on stabilised sediment surfaces. The microorganisms included coccoids, filaments and rare rod-shaped organisms associated with microbial polymer (EPS). The preserved microbial community was apparently dominated by chemotrophic organisms but some locally transported filaments and filamentous mat fragments indicate that possibly photosynthetic mats formed nearby. Both microorganisms and sediments were silicified during very early diagenesis.There are no macroscopic traces of fossilised life in these volcanic sediments and sophisticated instrumentation and specialized sample preparation techniques are required to establish the biogenicity and syngenicity of the traces of past life. The fact that the traces of life are cryptic, and the necessity of using sophisticated instrumentation, reinforces the challenges and difficulties of in situ robotic missions to identify past life on Mars. We therefore recommend the return of samples from Mars to Earth for a definitive search for traces of life.     

The Mineralogy,petrology and geochemistry of lunar samples - a review

Crystallization from the molten state has been an important process for the formation of rocks on the Moon; the phenomenon of fractional crystallization is therefore discussed. The principal chemical and mineralogical features of the Apollo 11, 12 and 14 basaltic crystalline rocks are described, and an account is given of other rock types and minerals which are represented among the coarser particles in the lunar soils. A comparison is made between the chemical compositions (major, minor and trace element concentrations) of rocks and soils.Based upon the above data, one possible model for the outer shell of the Moon is presented, which consists of an outer layer of Al-rich rocks underlain by a layer which is more ferromagnesian in character. Partial melting of the latter was probably responsible for the extrusion of lavas at the surface which spread to form the basalts (Apollo 11 and 12) of the non-circular maria. The Apollo 14 (Fra Mauro) basalts are relatively enriched in potassium, rare earth elements, zirconium, phosphorus and certain other elements and may derive from partial melting of the more aluminous upper layer.The separation of the outer Moon into two layers could have occurred through gravity-aided fractional crystallization at an early stage (first few hundred m yr) in lunar history.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971.     

Diffuse scattering of radar on the surface of Venus: Origin and implications for the distribution of soils

Previous analysis of PV altimeter data has shown that ~25% of the surface of Venus is characterized by low values of reflectivity, interpreted as being due to the presence of porous materials such as soils. However, examination of a corrected reflectivity data set in combination with PV altimeter data suggests that no more than 5% of the surface of Venus is covered by soils more than several to tens of cm in depth. Most regions of apparent low reflectivity are instead interpreted to be due to the presence of small (5–50 cm) roughness elements on the surface that cause diffuse scattering at the 17 cm PV wavelength. Regions of low apparent reflectivity are of interest because of a correlation with tessera, a complex tectonic unit mapped from Venera 15/16 SAR data. Regions of tessera are characterized by a complex system of intersecting ridges and valleys thought to be of tectonic origin. Examination of possible models for the form of diffuse scatterers in the tessera suggests that they are rock fragments and originate from a mass-wasting process that is linked to the rugged nature of the terrain. Further, these diffuse scatterers are associated with other tectonic landforms, suggesting that they originate as part of tectonic deformation of the surface. Viewed from a geologic standpoint, the PV data sets are important tools for understanding tectonic, volcanic, and degradational processes on Venus, as well as for future interpretation of data from the Magellan mission.     

Rain infiltration and crust formation in the extreme arid zone of the Atacama Desert, Chile

A key question in understanding life on Mars under dry(ing) conditions is how arid soils respond to small levels of liquid water. We have conducted a series of simulated rain experiments in the hyperarid core region of the Atacama Desert. Rain amounts from 0.24 to 3.55 mm were applied in the early evening to the soil. We conclude that rain events of less than 1 mm do not saturate the surface, and the soil humidity at the surface remains below 100%. Rain events of 2 mm or more generate free water in the pore space of the soil surface, which may be necessary to support biological activity in the soil. The crust on the surface of the soil is a strong barrier to the diffusion of subsurface moisture and subsequent evaporation. Our results show that once the relative humidity in hyperarid soils begins to fall below 100% the rate of decrease is quite rapid. Thus, the precise value assumed for the limits of life or water activity, do not appreciably change the time of water availability resulting from small desert rains. The Atacama Desert results may be applied to models of (H₂O) wetting in the upper soils of Mars due to light rains, melting snow and heavy precipitating fog.     

MAJOR ELEMENT COMPOSITION OF GLASSES IN THREE APOLLO 15 SOILS

Approximately 180 glasses in each of three Apollo 15 soils have been analyzed for nine elements. Cluster analysis techniques allow the recognition of preferred glass compositions that are equated with parent rock compositions Green glass rich in Fe and Mg, poor in Al and Ti may be derived from deep seated pyroxenitic material now present at the Apennine Front. Fra Mauro basalt (KREEP) is most abundant in the LM soil and is tentatively identified as ray material from the Aristillus-Autolycus area. Highland basalt (anorthositic gabbro), believed to be derived from the lunar highlands, has the same composition as at other landing sites, but is less abundant. The Apennine Front is probably not true highland material but may contain a substantial amount of material with the composition of Fra Mauro basalt, but lacking the high-K content. Glasses with mare basalt compositions are present in the soils and four subgroups are recognized, one of which is compositionally equivalent to the large Apollo 15 basalt samples     

Astrobiological significance of the sabkha life and environments of southern Tunisia

In high-salinity and water-scarce environments, such as in hot and dry deserts, species develop adaptive strategies that are necessary for living in such harsh conditions. Continental ephemeral salt lakes (sabkhas) with periodic flooding from subsurface groundwater followed by high salt concentrations, such as the ones of the northern Africa Chotts, rank among the geological settings wherein the combined effect of salt concentration and fluctuation of water availability make the environment unstable and can thereafter lead to extreme changes. The present study investigates the continental sabkha environments of southern Tunisia, in which ecological niches (i.e. water and salt precipitates, including halite, gypsum, and dolomite) host microbial life. Halophilic microorganisms can be trapped in the extensive saline crusts of halite and gypsum, which can be regarded as the first step of their delivery to the fossil record. The study of halophiles can provide clues for the understanding of life strategies in extreme terrestrial environments, such as sabkhas, which are potential good terrestrial analogs for evaporite-bearing Martian deposits.     

Cosmic rays and terrestrial life: A brief review

“The investigation into the possible effects of cosmic rays on living organisms will also offer great interest.” – Victor F. Hess, Nobel Lecture, December 12, 1936High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing it, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ∼3 billion years in presence of this background radiation, which itself has varied considerably during the period [1], [2], [3]. As demonstrated by the Miller–Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.     

X-ray digital imaging petrography of lunar mare soils: modal analyses of minerals and glasses

It is essential that accurate modal (i.e., volume) percentages of the various mineral and glass phases in lunar soils be used for addressing and resolving the effects of space weathering upon reflectance spectra, as well as for their calibration such data are also required for evaluating the resource potential of lunar minerals for use at a lunar base. However, these data are largely lacking. Particle-counting information for lunar soils, originally obtained to study formational processes, does not provide these necessary data, including the percentages of minerals locked in multi-phase lithic fragments and fused-soil particles, such as agglutinates. We have developed a technique for modal analyses, sensu stricto, of lunar soils, using digital imaging of X-ray maps obtained with an energy-dispersive spectrometer mounted on an electron microprobe. A suite of nine soils (90 to 150 micrometers size fraction) from the Apollo 11, 12, 15, and 17 mare sites was used for this study. This is the first collection of such modal data on soils from all Apollo mare sites. The abundances of free-mineral fragments in the mare soils are greater for immature and submature soils than for mature soils, largely because of the formation of agglutinitic glass as maturity progresses. In considerations of resource utilization at a lunar base, the best lunar soils to use for mineral beneficiation (i.e., most free-mineral fragments) have maturities near the immature/submature boundary (Is/FeO approximately or = 30), not the mature soils with their complications due to extensive agglutination. The particle data obtained from the nine mare soils confirm the generalizations for lunar soils predicted by L.A. Taylor and D.S. McKay (1992, Lunar Planet Sci. Conf. 23rd, pp. 1411-1412 [Abstract]).     

Fast tidal cycling and the origin of life

Replicating prebiotic polymers are thought to predate the emergence of true life-forms. The initial mode of replication, a prerequisite for Darwinian selection, is unknown, but demands an explanation based on local physicochemistry. Dual consideration of the conditions of the early terrestrial surface, with the unusual physicochemical properties of nucleic acids like DNA, could explain the emergence of nucleic acids as key biomolecules. The early impact that produced the Moon, and fast terrestrial rotation, subjected coastal areas 3.9 Ga ago to rapid tidal flooding (dilution) and drying (concentration), with a likely periodicity in the range of 2-6 h, and could have provided a driving force for cyclic replication of early biomolecules. Such a mechanism applies only to molecules capable of association/polymerization at high salt concentration, and of dissociation at low salinity. Nucleic acids meet these criteria. It is suggested that tidal cycling, resembling the polymerase chain reaction (PCR) mechanism, could only replicate and amplify DNA-like polymers. This mechanism suggests constraints on the evolution of extra-terrestrial life.     

Drilling in ancient permafrost on Mars for evidence of a second genesis of life

If life ever existed on Mars, a key question is the genetic relationship of that life to life on Earth. To determine if Martian life represents a separate, second genesis of life requires the analysis of organisms, not fossils. Ancient permafrost on Mars represents one potential source of intact, albeit probably dead by radiation, Martian organisms. Strong crustal magnetism in the ancient heavily cratered southern highlands between 60 and 80°S and at about 180°W indicates what may be the oldest, best preserved ice-rich permafrost on Mars. Drilling to depths of 1000 m would reach samples unaffected by possible warming due to cyclic changes in Mars’ obliquity. When drilling into the permafrost to retrieve ancient intact Martian organisms, it is necessary to take special precautions to avoid the possibility of contamination. Earth permafrost provides an analog for Martian permafrost and convenient sites for instrument development and field testing.     

Final frontiers: the hunt for life elsewhere in the Universe

This paper seeks to review the likelihood of unearthing evidence of the existence of life elsewhere in the Universe. Although it has been demonstrated that life can thrive in the severest of conditions on Earth, detecting its presence in similarly habitable zones elsewhere is proving to be an extremely complex issue. There are many reasons for this, the major ones being that the distances involved are vast; the low potential signal to noise ratio, spatial and spectral resolutions arising from planets with biospheres; and biosignals themselves can be misleading. New telescopes with improved technology are on the horizon which will extend our capabilities, but it is still doubtful that any exploration could venture beyond the borders of our galaxy. Moreover, caution needs to be exercised when assessing the signals emitted by biomarkers as these could be produced abiotically. However, if the focus of the search should be concentrated around the area of M dwarf stars then, as we begin to understand the nature of habitable zones, our chances of eventually achieving our goals will be enhanced.     

Light and dark soils at the apollo 16 landing site

On the basis of inert gas systematics alone, the soilsnow near the surface at the Apollo 16 landing site can be divided into three major groups: Group I (North Ray Crater Soils), Group II (Light Soils), and Group III (Dark Soils). Only five soils do not fit this scheme. The inert gas-based classification is correlated with the chemistry of the soils. Group I soils are relatively poor in K, Fe, Ti and Zn, compared to Group II and III soils. The classification is also correlated with reflectivity. Group I and II soils are generally the light soils in the landing area, while the Group III soils are the dark soils. The groups are not randomly distributed in the landing area. Group I soils occur only at stations 11 and 13 on the ejecta blanket of North Ray Crater. Group II soils occur abundantly at stations 1 and 2, and in spots on Stone Mountain. Group III soils are abundant on Stone Mountain and at station 10. We suggest here that Group I soils are principally derived from the light friable unit, one of the three units inside North Ray Crater, as described by Ulrich. We suggest that Group II soils are mainly derived from the light matrix breccia unit. Group III soils are mixtures of materials from all three units. We conclude that soils with the properties of Group III soils have been at the surface continuously for long times. However, going backwards in time, these soils probably had increasingly larger (Ar⁴⁰/Ar³⁶)t ratios. The ejecta blanket of North Ray Crater is a temporary ‘anomaly’ in the landing site. However, soils with the properties of Group I soils, but with larger (Ar⁴⁰/Ar³⁶)t ratios may turn up in Apollo 16 core tubes. The Group II soils show a record of solar wind exposure in the distant past (i.e., they have relatively large Art ⁴⁰/ARt ³⁶ ratios). From this we conclude that the regolith at Apollo 16 contains sizeable ‘pockets’ or horizons at depth which are the sources of the Group II soils. The materials in these pockets may be akin to soil 61 220.     

DNA sequencing and predictions of the cosmic theory of life

The theory of cometary panspermia, developed by the late Sir Fred Hoyle and the present author argues that life originated cosmically as a unique event in one of a great multitude of comets or planetary bodies in the Universe. Life on Earth did not originate here but was introduced by impacting comets, and its further evolution was driven by the subsequent acquisition of cosmically derived genes. Explicit predictions of this theory published in 1979–1981, stating how the acquisition of new genes drives evolution, are compared with recent developments in relation to horizontal gene transfer, and the role of retroviruses in evolution. Precisely-stated predictions of the theory of cometary panspermia are shown to have been verified.     

Exobiology, the study of the origin, evolution and distribution of life within the context of cosmic evolution: a review

The primary goal of exobiological research is to reach a better understanding of the processes leading to the origin, evolution and distribution of life on Earth or elsewhere in the universe. In this endeavour, scientists from a wide variety of disciplines are involved, such as astronomy, planetary research, organic chemistry, palaeontology and the various subdisciplines of biology including microbial ecology and molecular biology. Space technology plays an important part by offering the opportunity for exploring our solar system, for collecting extraterrestrial samples, and for utilizing the peculiar environment of space as a tool. Exobiological activities include comparison of the overall pattern of chemical evolution of potential precursors of life, in the interstellar medium, and on the planets and small bodies of our solar system; tracing the history of life on Earth back to its roots; deciphering the environments of the planets in our solar system and of their satellites, throughout their history, with regard to their habitability; searching for other planetary systems in our Galaxy and for signals of extraterrestrial civilizations; testing the impact of space environment on survivability of resistant life forms. This evolutionary approach towards understanding the phenomenon of life in the context of cosmic evolution may eventually contribute to a better understanding of the processes regulating the interactions of life with its environment on Earth.