morphologic stratigraphic and morphometric investigations of valley networks in eastern libya montes mars implications for the noachian hesperian climate change dendritic valley networks and broad longitudinal valleys are widespread within the eastern libya montes region the morphologic characteristics of the studied dendritic valleys especially their occurrence at local summits provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater induced processes our crater counts and model ages show that the dendritic valley networks average age 4 0 ga formed earlier than the longitudinal valley systems average age 3 7 ga both fluvial forms indicate a temporal change of the erosive environment at the noachian hesperian transition at 3 8 ga our results suggest that the fluvial activity within our investigation area lasted for 800 my from 4 1 ga to 3 3 ga the dendritic valleys show valley densities between 0 12 km 1 and 0 57 km 1 indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on mars

a spectroscopic method for identifying terrestrial biocarbonates and application to mars abstract searching for traces of extinct and or extant life on mars is one of the major objectives for remote sensing and in situ exploration of the planet in previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples in the form of fresh shells and fossils of different ages whose biotic origin is easily recognizable the goal was to discriminate them from their abiotic counterparts in general it is difficult to identify biotic signatures especially when the organisms inducing the carbonate precipitation have low fossilization potential i e microbes bacteria archaea a wide variety of microorganisms are implicated in carbonate genesis and their direct characterization is very difficult to evaluate by traditional methods both in ancient sedimentary systems and even in recent environments in the present work we apply our analysis to problematic carbonate samples in which there is no clear evidence of controlled or induced biomineralization this analysis indicates a very likely biotic origin of the aragonite samples under study in agreement with the conclusion previously reported by guido et al 2007 who followed a completely different approach based on a complex set of sedimentary petrographic geochemical and biochemical analyses we show that our method is reliable for discriminating between biotic and abiotic carbonates and therefore it is a powerful tool in the search for life on mars in the next generation of space missions to the planet

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position abstract interrill runoff and sediment yield from a topsoil having essentially textural pores and from another with structural pores were measured in the laboratory under simulated rain to investigate the effects of cover and positions of rock fragments the results reveal that the relation between the cover of rock fragments and interrill runoff or sediment yield can be negative as well as positive porosity in the soil near rock fragments determines both the type of relation and the degree to which the positions of rock fragments affect this relation rock fragments increase runoff and sediment yield when well embedded in a surface seal i e a top layer with essentially textural pore spaces a negative relation occurs either where rock fragments are partly embedded in a top layer with structural porosity or where the rock fragments rest on the surface of a soil having either textural or structural pore spaces the time at which macropores at the soil surface close is crucial for then the effect of the cover of rock fragments on the generation of runoff switches from reduction to an increase since cover can have an ambivalent effect on the hydrological and erosion response descriptions of topsoils containing rock fragments should include the type of soil porosity as well as the positions of rock fragments

empirical relations for the sediment transport capacity of interrill flow experiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters such as effective stream power and shear velocity different sediments were used in order to study the effect of grain size the proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent the proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models

tectonic reconstructions for paleobathymetry in drake passage abstract a minimum complexity tectonic reconstruction based on published and new basin opening models depicts how the scotia sea grew by cenozoic plate divergence dismembering a jurassic sheared margin of gondwana part of the jurassic early cretaceous ocean that accreted to this margin forms the core of the central scotia plate the arc plate above a trench at the eastern end of the scotia sea which migrated east away from the antarctic and south american plates a sequence of extensional basins opened on the western edge of the central scotia plate at 50 30 ma decoupled from the south american plate to the northwest by slow motion on a long transform fault succeeding the basins seafloor spreading started around 30 ma on the west scotia ridge which propagated northwards in the 23 17 ma period and ceased to operate at 6 ma the circuits of plate motions inside and outside the scotia arc are joined via rotations that describe antarctic central scotia plate motion in powell basin until 20 ma and along the south scotia ridge thereafter the modelled relative motion at the northern edge of the scotia sea is thus constrained only by the plate circuit but nonetheless resembles that known coarsely from the geological record of tierra del fuego a paleobathymetric interpretation of nine time slices in the model shows drake passage developing as an intermediate depth oceanographic gateway at 50 30 ma with deep flow possible afterwards initially this deep flow would have been made tortuous by numerous intermediate and shallow barriers a frontal pattern resembling that in the modern scotia sea would have awaited the clearance of significant barriers by continuing seafloor spreading in the scotia sea at 18 5 ma at shag rocks passage and after 10 ma southeast of south georgia

hydrothermal formation of clay carbonate alteration assemblages in the nili fossae region of mars abstract the compact reconnaissance imaging spectrometer for mars crism has returned observations of the nili fossae region indicating the presence of mg carbonate in small

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

identification of carbonate rich outcrops on mars by the spirit rover decades of speculation about a warmer wetter mars climate in the planet s first billion years postulate a denser co2 rich atmosphere than at present such an atmosphere should have led to the formation of outcrops rich in carbonate minerals for which evidence has been sparse using the mars exploration rover spirit we have now identified outcrops rich in magnesium iron carbonate 16 to 34 weight percent in the columbia hills of gusev crater its composition approximates the average composition of the carbonate globules in martian meteorite alh 84001 the gusev carbonate probably precipitated from carbonate bearing solutions under hydrothermal conditions at near neutral ph in association with volcanic activity during the noachian era

surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments the influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer a measure of seal strength by means of a torvane slope has a negative influence on sealing intensity for a constant per cent of simulated stone cover sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer explanations for these findings are given and some implications are further discussed

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

characterization of the martian surface deposits by the mars pathfinder rover sojourner sojourner the mars pathfinder rover discovered pebbles on the surface and in rocks that may be sedimentary not volcanic in origin surface pebbles may have been rounded by ares flood waters or liberated by weathering of sedimentary rocks called conglomerates conglomerates imply that water existed elsewhere and earlier than the ares flood most soil like deposits are similar to moderately dense soils on earth small amounts of dust are currently settling from the atmosphere

evidence for mg rich carbonates on mars from a 3 9 μm absorption feature abstract the origin and nature of the early atmosphere of mars is still debated the discovery of sulfate deposits on the surface coupled with the evidence that there are not large abundances of carbonates detectable on mars in the optically accessible part of the regolith leaves open different paleoclimatic evolutionary pathways even if carbonates are responsible for the feature observed by tes and mini tes at 6 76 m alternative hypotheses suggest that it could be due to the presence of hydrated iron sulfates his carbonates can be discerned from his by investigating the spectral region in which a strong overtone carbonate band is present the planetary fourier spectrometer on board the mars express spacecraft has acquired several thousand martian spectra in the range 1 2 45 m since january 2004 most of which show a weak absorption feature between 3 8 and 4 m a similar feature was observed previously from the earth but its origin could not be straightforwardly ascribed to surface materials and specifically to carbonates here we show the surficial nature of this band that can be ascribed to carbonate mixed with the martian soil materials the materials that best reproduce the detected feature are mg rich carbonates huntite camg3 co3 4 and or magnesite mgco3 the presence of carbonates is demonstrated in both bright and dark martian regions an evaluation of the likeliest abundance gives an upper limit of 10 wt the widespread distribution of carbonates supports scenarios that suggest carbonate formation occurred not by precipitation in a water rich environment but by weathering processes

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

diverse aqueous environments on ancient mars revealed in the southern highlands high resolution spectral images reveal many new exposures of hydrated minerals across the noachian southern highlands of mars several different phyllosilicates are observed with inferred accompanying phases ranging from zeolites to sulfates to chlorides each in distinct geologic settings hydrated sulfates are observed in several locations at mid latitudes and likely formed independently from the equatorial sulfates these assemblages suggest a greater diversity of aqueous environments on ancient mars than has previously been recognized and their distribution implies that alteration was widespread during the noachian period not restricted to a few locations

study of terrestrial fossils in phyllosilicate rich soils implication in the search for biosignatures on mars abstract the search for biosignatures in the soil of mars is a major objective of the planet exploration but the detection of such structures is not straightforward due to the degradation of the organic material in a previous work our group has analyzed the spectral reaction to thermal processing of biomineral carbonate samples including fresh and fossil shells we found that two terrestrial fossil shells collected from clay deposits preserve their biomineral characteristics much better than coeval fossils not embedded in clay layers in the present paper we extend our analysis to a set of fossils found in three different terrestrial clay deposits our results confirm that the level of degradation may be much lower than the standard values if fossils are surrounded by clay minerals as a result these fossils have a spectroscopic response to thermal treatment which make them much more distinguishable from their abiotic counterparts than coeval fossils not collected from clay deposits this result implies that the phyllosilicates regions recently discovered on mars may represent very interesting environments that can provide conditions favorable to preserve evidence of biomarkers and hence can be regarded as good candidate locations for their detection

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

ancient mars wet in many places new results from the mars express orbiter mission reveal multiple deposits of minerals formed in the presence of liquid water they reinforce the conclusion that ancient mars was warmer and wetter than it is today and increase the number of promising localities to search for evidence of past life

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

phyllosilicates in the mawrth vallis region of mars 1 omega mars express has discovered large outcrops rich in phyllosilicates in the region of mawrth vallis mars around 20 w 25 n the region is located in noachian highly cratered terrains close to the limit of the martian dichotomy where the outflow channel mawrth vallis cuts the highlands we have examined this region using omega spectra of the surface from 0 9 m to 2 6 m with spatial sampling from 500 m to 3 km offering a full coverage of the region omega spectra show two broad bands centered at 1 m and 2 2 m revealing the presence of clinopyroxene on dark surfaces phyllosilicates have been identified by absorption bands at 1 4 m 1 9 m and 2 2 or 2 3 m comparison with laboratory spectra reveals similarities with al oh smectites such as montmorillonites or fe or mg oh smectites such as nontronite a precise location of the phyllosilicate rich areas on visible hrsc images indicates that they are placed exclusively on bright outcrops mostly on the plateaus dated to the noachian period on hrsc and moc images the phyllosilicate rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick the phyllosilicate rich unit corresponds to a geological unit more than 100 m thick over a horizontal extension approximately of 300 km 400 km this unit implies a large volume of altered rocks either in situ or after transport and deposition in noachian terrains revealing a different climatic and geologic environment from the present one

infrared spectroscopy of microbially induced carbonates and past life on mars abstract a number of evidences as the past presence of water a denser atmosphere and a mild climate suggest that on early mars environmental conditions should have been favourable to the emergence of life therefore if life actually developed on mars a few hundreds of million years ago or even more recently some biomarkers may still be present in several previous papers based on laboratory analysis we have investigated the modifications induced by thermal processing in the mid infrared spectra of carbonate samples in the form of fresh shells and fossils of different ages skeletal remains of already complex terrestrial life whose biotic origin is not questionable in this way we have been able to develop a spectroscopic method for discriminating biotic samples from their abiotic counterparts in this work we show that our method can be successfully applied also to microbialites i e bio induced carbonates deposits and particularly to stromatolites the laminated fabric of microbialites some of which are among the most primitive and oldest traces of biological activity on earth this result is of valuable importance since such primitive living organisms can be considered good analogues for putative martian life forms

photochemical and climate consequences of sulfur outgassing on early mars abstract ancient mars might have been warm and wet compared to today but climate models have trouble reproducing this warmth partly because of the faintness of the young sun and partly because of inherent limitations to co2 h2o greenhouse warming in particular rayleigh scattering of incoming sunlight by a dense co2 rich atmosphere leads to a high planetary albedo thereby reducing the amount of sunlight absorbed by the planet it has been recently suggested that the presence of 1 100 ppmv so2 in mars early atmosphere might have provided enough additional greenhouse warming to maintain a warm wet early mars we show however that this warming should have been more than offset by cooling from sulfate and sulfur aerosols in early martian atmosphere hence the paradox of mars early climate remains unresolved