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

evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater 1 a single scoop of the rocknest aeolian deposit was sieved 150 m and four separate sample portions each with a mass of 50mg were delivered to individual cups inside the sample analysis at mars sam instrument by the mars science laboratory rover ss ample acquisition system the samples were analyzed separately by the sam pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes several chlorinated hydrocarbons including chloromethane dichloromethane trichloromethane a chloromethylpropene and chlorobenzene were identified by sam above background levels with abundances of 0 01 to 2 3nmol the evolution of the chloromethanes observed during pyrolysis is coincident with the increase in o2 released from the rocknest sample and the decomposition of a product of n methyl n tert butyldimethylsilyl trifluoroacetamide mtbstfa a chemical whose vapors were released from a derivatization cup inside sam the best candidate for the oxychlorine compounds in rocknest is a hydrated calcium perchlorate ca clo4 2 nh2o based on the temperature release of o2 that correlates with the release of the chlorinated hydrocarbons measured by sam although other chlorine bearing phases are being considered laboratory analog experiments suggest that the reaction of martian chlorine from perchlorate decomposition with terrestrial organic carbon from mtbstfa during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by sam chlorobenzene may be attributed to reactionsofmartian chlorine released during pyrolysiswith terrestrial benzene or toluene derived from 2 6 diphenylphenylene oxide tenax on the sam hydrocarbon trap at this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons nor do we exclude the possibility that future sam analyses will reveal the presence of organic compounds native to the martian regolith

a search for endogenous amino acids in the martian meteorite eeta79001 abstract the antarctic shergottite eeta79001 is believed to be an impact ejected fragment of the planet mars samples of the carbonate white druse and the basaltic lithology a components from this meteorite have been found to contain amino acids at a level of approximately 1 ppm and 0 4 ppm respectively the detected amino acids consist almost exclusively of the l enantiomers of the amino acids commonly found in proteins and are thus terrestrial contaminants there is no indication of the presence of aminoisobutyric acid one of the most abundant amino acids in several carbonaceous chondrites the relative abundances of amino acids in the druse material resemble those in antarctic ice suggesting that the source of the amino acids may be ice meltwater the level of amino acids in eeta79001 druse is not by itself sufficient to account for the 600 700 ppm of volatile c reported in druse samples and suggested to be from endogenous martian organic material however estimates of total terrestrial organic c present in the druse material based on our amino acid analyses and the organic c content of polar ice can account for most of the reported putative organic c in eeta79001 druse

biomimetic properties of minerals and the search for life in the martian meteorite alh84001 the existence of extraterrestrial life was heralded by controversial claims made in 1996 that the martian meteorite alh84001 harbored relics of ancient microorganisms we review here the accumulated evidence for and against past extraterrestrial life in this martian meteorite the main pro life arguments the presence of polycyclic aromatic hydrocarbons magnetite crystals carbonate globules and structures resembling terrestrial life forms known as nanobacteria can be deemed ambiguous at best although these criteria are compatible with living processes each one of them can be explained by nonliving chemical processes by undergoing amorphous to crystalline transformations and binding to multiple substrates including other ions and simple organic compounds minerals especially those containing carbonate have been shown to display biomimetic properties producing forms that resemble bacteria this simple and down to earth explanation can account fully for the existence of mineral entities resembling put

issues involved in a martian sample return integrity preservation and the curation and analysis planning team for extraterrestrial materials captem position returning geological samples from mars is the next logical step as part of an integrated exploration program and is the critical subsequent stage in the search for evidence of life on the red planet analysis of such samples on earth will generally produce data of superior accuracy and precision than can be accomplished in situ on the martian surface and such data will be invaluable in providing ground truth for remotely sensed observations however obtaining meaningful data requires that the samples returned to earth suffer little or preferably no compositional or morphological changes during collection on mars transit to earth entry into earth s atmosphere impact on the surface and long term curation this paper presents recommendations from nasa s committee for curation and analysis planning team for extraterrestrial materials captem for preserving the integrity of martian samples during a return mission potential contaminants include dead bacteria on the outbound spacecraft and materials that come into contact with the samples during collection and storage therefore it is recommended that the spacecraft be sterilized and cleaned at least to pathfinder standards with the components that interact with the samples having a higher degree of cleanliness furthermore it is recommended that only pure homogeneous materials should be used for components that come into contact with the samples the adverse effects of temperature on the samples are explored and it is demonstrated that heat sterilization or undue temperature increases in transit or reentry have the potential to destroy important mineralogical and geochemical information concomitant with this will be degassing of the samples and stable isotopic fractionation therefore it is recommended that samples be kept at 240 k or below during transit reentry and curation it is further recommended that heat sterilization not be used except in extreme circumstances and other sterilization techniques such as radiation be explored while the purpose of this paper is not to design a sample return mission the recommendations presented here are intended to act as guidelines for returning martian samples in their pristine state in essence any procedure or piece of equipment that has the potential to compromise the pristinity of martian samples during the collection transportation or curation needs to be fully evaluated by a scientific committee with the requisite expertise prior to implementation captem is willing to serve in such a capacity if requested by nasa

formation and relative ages of maskelynite and carbonate in alh84001 the morphology and stoichiometry of feldspathic glass in the martian meteorite alh84001 indicates it is maskelynite a diaplectic glass rather than a flowed glass although this glass was heterogeneously affected by a tertiary set of processes an impact event with shock pressures in excess of 31 gpa was needed to convert the original plagioclase an36ab60or4 to maskelynite carbonate is intimately associated with the maskelynite and the carbonate s radiating crystalline fabric and globular forms suggest it was produced after plagioclase was converted to maskelynite textures also suggest carbonate was produced at the expense of maskelynite in a dissolution precipitation reaction that involved a carbonic fluid this fluid system is tentatively estimated to have been active for at least a few years at temperatures 300 c based on dissolution rates of plagioclase in mildly to strongly alkaline hydrothermal systems which is the only analogue currently available this reaction does not need to be mitigated by microbial life neither are bacteria needed to produce the radiating textures and globular forms of carbonate which may instead reflect kinetic phenomena associated with crystal nucleation and growth because the carbonate was produced at the expense of maskelynite it is younger than maskelynite which has previously been shown to have last degassed 3 92 0 04 ga turner et al 1997 however the specific age of the carbonate and the carbonic fluid system remains unknown

trace metals in porewater of surface sediments and their bioavailability in jiaozhou bay qingdao china samples of porewater and the edible tissue of mottled clams ruditapes variegatus were collected simultaneously at each of 12 stations from jiaozhou bay near qingdao china in june of 2003 chemical analysis focused on trace metals and major elements porewater concentrations of cd cr pb and zn were distributed in a bimodal fashion among the 12 stations with mean concentrations at six of the stations being 8 32 times mean values at the other six stations the concentrations of the same metals in clams were remarkably similar among stations the coefficients of variation being only 12 37 calculations performed with the computer program phreeqc indicated that pb and cr in porewater were present only in the 2 and 3 states respectively and because dissolved cd and zn exist only in the 2 state the bimodal distribution of these four metals likely reflects secondary effects associated with their scavenging by fe and or mn under oxidizing conditions and subsequent dissolution in the reducing environment of the porewaters consistent with this hypothesis is the fact that the distribution of high and low metal concentrations was closely correlated with the granularity of the sediment with lower metal concentrations associated with relatively coarse sediment comparison of published biological concentration factors with the ratios of metal concentrations in the clams to porewater metal concentrations indicated that the porewaters were not the primary sources of the metals in the clams mixing processes in the bay likely account for the rather uniform concentrations of metals in clam tissue

drastic desalination of small lakes in east siberia russia in the early twentieth century inferred from sedimentological geochemical and palynological composition of small lakes reconstruction of temporal and spatial climate development on a seasonal basis during the last few centuries may help us better understand modern day interplay between natural and anthropogenic climate variability the objective of this paper is to reconstruct hydrology and landscape changes of east siberia during the termination of the little ice age and the subsequent recent warming we analysed sediment samples from the saltwater sulfatnoe lake bolshoye alginskoe and freshwater shuchie lake using high resolution x ray fluorescence spectroscopy at 1 mm scan resolution fourier transform infrared techniques and pollen analyses the depth age models of the cores were constructed by 210pb activity using the constant rate of supply model the lake sediment cover of these lakes began to form from ca 1870 three significant periods 1870 1895 1895 1925 and from 1925 to the present were defined in hydrology and chemical regime of these lakes for the past 140 years lake levels were extremely low and high saturated with salts during the final period of the little ice age lake levels began to slowly rise from 1870 to 1895 and vegetation was poor at that period intensive desalination of the lakes occurred in 1895 1925 and environment conditions were temperate and favourable for the majority of the taxa of the regional vegetation regional precipitation significantly increased and water saturation of the catchments was high from 1925 to the present the chemical precipitation of carbonate stopped completely in lake shichie and reduced considerably in lake sulfatnoe and b alginskoe strong increasing trend of weathering of the lake catchments began in 1970 and still continues

abiotic synthesis of polycyclic aromatic hydrocarbons on mars thermochemical calculations of metastable equilibria are used to evaluate the stability of condensed polycyclic aromatic hydrocarbons pahs in cooling thermal gases and hydrothermal fluids on ancient mars which are roughly similar to their terrestrial counterparts the effects of temperature pressure the extent of pah alkylation and the relative stability of pahs and alkanes are considered inhibition of methane and graphite formation favors synthesis of metastable mixtures of hydrocarbons from aqueous or gaseous co co2 and h2 below 200 300 c high temperature quenching of h2 and co in volcanic and impact gases and dynamic hydrothermal fluids also favor the synthesis of hydrocarbons in addition an excess of co in cooling systems relative to equilibrium makes the synthesis from co and h2 more favorable energetically than from co2 and h2 both the co h2 reactions through fischer tropsch ft type processes and the co2 h2 reactions could be catalyzed by magnetite volcanic gases and hydrothermal fluids related to mafic and ultramafic magmas and rocks are more favorable for ft type synthesis than those associated with oxidized fe2o3 bearing rocks and regolith we conclude that pahs and aliphatic hydrocarbons on mars and earth could be formed without the contribution of biogenic carbon some pahs could be formed because of pyrolysis of other hydrocarbons formed earlier by the ft type synthesis or other processes if the pahs found in the alh 84001 martian meteorite formed together with other hydrocarbons through ft type synthesis it may be possible to bracket the temperature of the synthesis the approach presented here can be generalized to study the synthesis of hydrocarbons in terrestrial volcanic and hydrothermal processes

trace elements in holocene sediments of the southern donana national park sw spain historical pollution and applications the multidisciplinary analysis of core sediments from donana national park south spain permits to delimitate both the paleoenvironmental changes and the geochemical evolution of this area during the holocene in a first phase 10 6 5 kyr cal this area was occupied by freshwater brackish marshes with periodical alternation of dry periods and humid intervals in a second phase these marshes were inundated during the flandrian transgression 6 5 kyr cal with the deposition of bioclastic sands the third phase 6 5 3 6 kyr cal is characterized by the transition to an old lagoon with unpolluted bottom sediments the geochemical concentrations of these clayey sediments can be used as a geochemical background for present day and future environmental evaluations of this area in the following 600 years approximately two tsunamis caused the partial infilling of this area with bioclastic marine sediments in the interval comprised between these two tsunamis this lagoon was polluted with heavy metals derived from historical mining activities this environmental contamination represents one of the oldest evidences of mining pollution in the world 3 kyr cal bp

petroleum generation an easy and widespread process in hydrothermal systems an overview abstract the conversion of organic matter to petroleum products by hydrothermal activity is an easy process occurring in nature in many types of environments geologically immature organic matter of marine sediments has been shown to be altered to petroleum products by this process in the guaymas basin escanaba trough bransfield strait and atlantis ii deep and this process probably occurs elsewhere in active sedimented rift systems contemporary organic detritus and or viable microorganisms are also converted in part to petroleum like products when they become entrained by turbulent mixing into hydrothermal vent waters resulting in their instantaneous hydrous pyrolysis this latter case occurs in hydrothermal vent fields without a sedimentary cover emanating directly from oceanic ridges as for example on the east pacific rise at 13 n and 21 n and on the mid atlantic ridge at 26 n this process is probably also ubiquitous for all actively venting sediment starved oceanic ridges the hydrocarbon products generated in these areas have been compared in terms of composition organic matter sources and analogy to reservoir petroleum they represent a major carbon source for chemosynthetic assimilation by vent biota and are compositionally similar to normal petroleum

is the cumulate paradigm at risk an extended discussion of the cumulate paradigm reconsidered a plot of p2o5 versus normative pyroxene for 43 rocks of skaergaard lza offered by mcbirney and hunter as a challenge to the orthocumulus hypothesis contains no data below 10 pyroxene by hypothesis the range between 0 and 10 pyroxene must be well populated for plagioclase olivine orthocumulates and therefore the rocks do not pass the first test of the orthocumulus hypothesis many lza rocks also contain more than the cotectic amount of pyroxene which should be regarded in part as a cumulus phase the remainder especially the poikilitic overgrowths can comfortably be ascribed to heteradcumulus growth such nucleation driven infiltration metasomatism cannot be distinguished from lateral or upward metasomatism using the data set presented the data can be evaluated entirely within the cumulate paradigm which also shows that new information is needed to evaluate competing hypotheses for the origin of these rocks many successful examples of orthocumulate and adcumulate growth have been demonstrated

chemical evolution of intercumulus liquid as recorded in plagioclase overgrowth rims from the skaergaard intrusion the intercumulus liquid of a crystal mush fills pore spaces and typically solidifies to form overgrowths on cumulus grains and poikilitic post cumulus minerals if the liquid is immobile solidification produces zoned intercumulus minerals as a result of progressive fractionation of the residual liquid convection within the mush results in buffering of the liquid composition and thus limits mineral zonation for fully solidified cumulates fossil changes in liquid composition or porosity are difficult to identify however detailed study of immobile minor components of plagioclase overgrowth rims can provide information about the progressive solidification of intercumulus material ti contents of plagioclase overgrowths in samples from the lowermost parts of the skaergaard intrusion show strong variations with anorthite content with decreasing xan ti concentrations first rise and then fall consistent with changing tio2 contents of the intercumulus liquid during solidification tio2 in plagioclase decreases sharply at an55 reflecting local saturation of fe ti oxides ti in clinopyroxene oikocrysts also falls rimward but zoning in faster diffusing species fe mg is limited other than slight reverse zones that may occur on the plagioclase margins xan falls continuously during crystallization the reverse zoning is interpreted as the result of compaction driven dissolution and reprecipitation of plagioclase the continual decrease in xan is exploited together with back scattered electron images of the cumulates to produce calibrated images showing regions of progressive crystallization this allows the regions crystallizing at each stage of solidification to be visualized these images show that the final remnants of interstitial melt were present in triangular pockets and as thin grain boundary melt films this approach can provide information about the progressive reduction of porosity during cumulate solidification

formation of meteorite hydrocarbons from thermal decomposition of siderite feco3 thermal decomposition of siderite has been proposed as a source of magnetite in martian meteorites laboratory experiments were conducted to evaluate the possibility that this process might also result in abiotic synthesis of organic compounds siderite decomposition in the presence of water vapor at 300 c generated a variety of organic products dominated by alkylated and hydroxylated aromatic compounds the results suggest that formation of magnetite by thermal decomposition of siderite on the precursor rock of the martian meteorite alh84001 would have been accompanied by formation of organic compounds and may represent a source of extraterrestrial organic matter in the meteorite and on mars the results also suggest that thermal decomposition of siderite during metamorphism could account for some of the reduced carbon observed in metasedimentary rocks from the early earth

carbonaceous micrometeorites from antarctica over 100 000 large interplanetary dust particles in the 50 500 micrometers size range have been recovered in clean conditions from approximately 600 tons of antarctic melt ice water as both unmelted and partially melted dehydrated micrometeorites and cosmic spherules flux measurements in both the greenland and antarctica ice sheets indicate that the micrometeorites deliver to the earth s surface approximately 2000x more extraterrestrial material than brought by meteorites mineralogical and chemical studies of antarctic micrometeorites indicate that they are only related to the relatively rare cm and cr carbonaceous chondrite groups being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals however there are also marked differences between these two families of solar system objects including higher c o ratios and a very marked depletion of chondrules in micrometeorite matter hence they are chondrites without chondrules thus the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles comets one of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early earth and more recently with the early history of the solar system

isotopic composition of carbonate in eeta 79001 and its relation to parent body volatiles calcite a probable extraterrestrial weathering product in the shergottite eeta 79001 has 13c 9 7 and 18o 21 0 in order to account for the large excess of 18o relative to the silicate substrate 18o 4 2 a parent body surface reservoir containing both water and carbon dioxide is required the inferred h2oco2 ratio is consistent with estimates for the degassed reservoir on mars

plagioclase in the skaergaard intrusion part 1 core and rim compositions in the layered series the anorthite content of plagioclase grains xan in 12 rocks from the layered series of the skaergaard intrusion has been studied by electron microprobe typically 30 core and 70 rim analyses per thin section mean core compositions vary continuously from an66 at the base of the layered series lza to an32 30 at the top on the other hand crystal rims are of approximately constant composition an50 1 from the lza to the lower middle zone mz above the mz core and rim compositions generally overlap profiles across individual plagioclase grains from the lower zone show that most crystals have an external zone buffered at xan 50 1 the simplest explanation for these features is that during postcumulus crystallization in the lower zone interstitial liquids passed through a density maximum this interpretation is consistent with proposed liquid lines of descent that predict silica enrichment of the liquid associated with the appearance of cumulus magnetite

adsorption of organic compounds on carbonate minerals 3 influence on dissolution rates abstract this is the third in a series of papers to investigate the role of organic compounds on wettability porosity and permeability of carbonate rocks these are important reservoir characteristics that influence the performance of petroleum reservoirs this paper reports dissolution studies to address diagenetic effects on carbonate porosity and permeability comparative dissolution measurements were performed to assess the influence of adsorbed organic material on the reactivity of calcite and dolomite in the geologic environment organic compounds that adsorb strongly on carbonate minerals fatty acids and carboxylated polymers were found to dramatically inhibit dissolution while weak adsorbates and nonadsorbates showed little or no effect on the dissolution rates experiments were performed at 20 50 and 80 c to examine the role of organic adsorbates at reservoir temperatures and the strong adsorbates inhibited dissolution at all temperatures experiments from various initial ph s confirmed that strong adsorption is an ionic interaction and demonstrated that the inhibition of dissolution is limited to ph s above 4 5 5 0

carbon oxygen and nitrogen isotopic compositions of possible martian weathering products in eeta 79001 abstract carbon and oxygen isotopic analyses of carbonate rich white druse material isolated from a contact between lithologies a and c of the eeta 79001 shergottite indicate that this component is probably extraterrestrial in origin and not simply an antarctic weathering product the 13c 6 8 and 18o 21 1 values of the calcium carbonate predominantly calcite are unlike 13 c 18 o combinations of most common terrestrial carbonates whether biogenic or abiogenic however 13c and 18o of the carbonates in eeta 79001 are very similar to the corresponding values for carbonates analysed from nakhla a meteorite closely allied to shergottites it seems apparent that the carbonate minerals in these snc meteorites were formed on the meteorites parent body mars isotopic analysis of nitrogen liberated during combustion of a carbonate rich fraction of eeta 79001 does not give any clear evidence for the 15n enriched component isolated from eeta 79001 lithology c glass and postulated as trapped martian atmosphere however substantial amounts of nitrogen were present the origin of these components is unclear but the low temperature of release poses some constraints

application of stable carbon isotopes to early biochemical evolution on earth the emergence and early evolution of life on earth have long been intriguing subjects for scientific inquiry and a continuous source of intel lectual excitement current work at this frontier proceeds along a number of different avenues and comprises a variety of disciplinary approaches that together strongly suggest that the earth was inhabited by life as early as almost 4 gyr ago the present state of the field as inferred from the results of a broad interdisciplinary approach has recently been summarized by j w schopf and coworkers cf schopf 1 983 it is with the advantage of such a synoptic view that the present review addresses a single facet of the theme namely the potential isotopic infer ences of the presence of co2 fixing autotrophic organisms for the carbon cycle of the early earth with biologically derived organic carbon as well as carbonates limestone dolomite etc abundantly preserved in sediments relevant isotopic evidence should have been encoded in the geologic record from its onset about 3 8 gyr ago it has been known since the pioneering studies by nier gulbransen 1939 murphey nier 1941 and rankama 1948 that the trans formation of inorganic carbon into living matter entails a marked bias in favor of the light isotope c2c with the heavy species l3c retained in the inorganic reservoir subsequent work performed by many investigators e g craig 1953 park epstein 1960 has confirmed that all common

hosts of hydrogen in allan hills 84001 evidence for hydrous martian salts in the oldest martian meteorite the martian meteorite allan hills alh 84001 contains d rich hydrogen of plausible martian origin leshin et al 1996 the phase identity of the host s of this hydrogen are not well known and could include organic matter mckay et al 1996 phlogopite brearley 2000 glass mittlefehldt 1994 and or other unidentified components of this rock previous ion microprobe studies indicate that much of the hydrogen in alh 84001 as texturally associated with concretions of nominally anhydrous carbonates glass and oxides boctor et al 1998 sugiura and hoshino 2000 we examined the physical and chemical properties of the host s of this hydrogen by stepped pyrolysis of variously pre treated subsamples a continuous flow method of water reduction and mass spectrometry eiler and kitchen 2001 was used to permit detailed study of the small amounts of this hydrogen poor sample available for study we find that the host s of d rich hydrogen released from alh 84001 at relatively low temperatures 500 c is soluble in orthophosphoric and dilute hydrochloric acids and undergoes near complete isotopic exchange with water within hours at temperatures of 200 to 300 c these characteristics are most consistent with the carrier phase s being a hydrous salt e g carbonate sulfate or halide the thermal stability of this material is inconsistent with many examples of such minerals e g gypsum and instead suggests one or more relatively refractory hydrous carbonates e g hydromagnesite hydrous salts particularly hydrous carbonates are common on the earth only in evaporite sabkha and hydrocryogenic weathering environments we suggest that much if not all of the martian hydrogen in alh 84001 was introduced in analogous environments on or near the martian surface rather than through biological activity or hydrothermal alteration of silicates in the crust

electrochemical processes in a crystal mush cyclic units in the upper critical zone of the bushveld complex south africa the upper critical zone ucz of the bushveld igneous complex displays spectacular layering in the form of cyclic units comprising a basal chromitite layer overlain by a sequence of silicate cumulates in the order from bottom to top pyroxenite norite anorthosite electron microprobe and laser ablation inductively coupled plasma mass spectrometry analyses of chromite and silicate minerals in layers between the ug2 chromitite and the merensky reef reveal variations in major and trace element compositions that defy explanation with existing models of cumulate mineral melt evolution the anomalous features are best developed at sharp contacts of chromitite with adjacent anorthosite and pyroxenite cumulates here chromite compositions change abruptly from high and constant mg mg fe 2 and fe 2 fe 3 ratios in chromitite layers to variable and generally lower values in chromite disseminated in silicate layers furthermore the composition of disseminated chromites varies depending on the host silicate assemblage for example in ti v and zn contents importantly the abrupt change in chromite composition across the chromitite silicate layer contacts is independent of the thickness of the chromitite layer and the estimated mass proportions of chromite to intercumulus liquid chemical variations in plagioclase are also abrupt and some are hard to reconcile with conventional models of re equilibration with intercumulus liquid among those features is the decoupling of alkalis from other incompatible lithophile elements in comparison with cumulus plagioclase intercumulus poikilitic plagioclase in chromitite layers is enriched in rare earth elements but strongly depleted in equally incompatible li k and rb strong alkali depletion is also observed in intercumulus pyroxene from ultramafic cumulates and chromitite layers to explain these features we propose a new model of post cumulus recrystallization which intensifies the modal layering in the crystal liquid mush producing the observed sequence of nearly monomineralic layers of chromitite pyroxenite and anorthosite that define the cyclic units the crucial element of this model is the establishment of redox potential gradients at contacts between chromite rich cumulates and adjacent silicate layers owing to peritectic reactions between the crystals and intercumulus melt because basaltic melts are ionic electrolytes with na as the main charge carrier the redox potential gradient induces electrochemical migration of na and other alkali ions selective mobility of alkalis can explain the enigmatic features of plagioclase composition in the cyclic units sodium migration is expected to cause remelting of previously formed cumulates and major changes in modal mineral proportions which may eventually result in the formation of sharply divided monomineralic layers the observed variations in ferric ferrous iron ratios in chromite from the cyclic units and fe distribution in plagioclase imply a redox gradient of

pollen event stratigraphy of the varved sediment of lake suigetsu central japan from 15 701 to 10 217 sg vyr bp suigetsu varve years before present description interpretation and correlation with other regions high resolution pollen data average interval between samples 15 years are reported on part of a varved sediment core from lake suigetsu japan spanning the interval 15 701 to 10 217 sg vyr bp suigetsu varve years before present this new record is compared with a previously proposed event stratigraphy based on pollen based reconstructed changes of mean annual temperature the deglacial climate history reconstructed at lake suigetsu resembles that observed in the north atlantic although the major boundaries of pollen zones are asynchronous with those in the north atlantic event stratigraphy by several centuries the onset of the late glacial interstadial occurred earlier in japan than in the north atlantic this demonstrates that the climate in japan was closely linked to the low latitude pacific sea surface temperatures that first reacted to orbital forcing conversely the onset of the subsequent cold reversal phase in japan lagged that of the north atlantic younger dryas by several centuries the duration of this cold phase was about the same as the younger dryas event but the amplitude was much reduced 4 2 c in mean annual temperature these findings support the hypothesis that this pan hemispheric cooling event was triggered by north atlantic forcing most probably by a meltwater pulse and an associated change in the north atlantic thermohaline circulation however the mechanism which transmitted the change in the north atlantic to the far east is unknown

polycyclic aromatic hydrocarbons pahs in antarctic martian meteorites carbonaceous chondrites and polar ice recent analyses of the carbonate globules present in the martian meteorite alh84001 have detected polycyclic aromatic hydrocarbons pahs at the ppm level mckay et al 1996 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 mcdonald and bada 1995 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 on mars

the origin of organic matter in the martian meteorite alh84001 stable carbon isotope measurements of the organic matter associated with the carbonate globules and the bulk matrix material in the alh84001 martian meteorite indicate that two distinct sources are present in the sample the d 13 c values for the organic matter associated with the carbonate globules averaged 26 and is attributed to terrestrial contamination in contrast the d 13 c values for the organic matter associated with the bulk matrix material yielded a value of 15 the only common sources of carbon on the earth that yield similar d 13 c values other then some diagenetically altered marine carbonates are c4 plants a d 13 c value of 15 on the other hand is consistent with a kerogen like component the most ubiquitous form of organic matter found in carbonaceous chondrites such as the murchison meteorite examination of the carbonate globules and bulk matrix material using laser desorption mass spectrometry ldms indicates the presence of a high molecular weight organic component which appears to be extraterrestrial in origin possibly derived from the exogenous delivery of meteoritic or cometary debris to the surface of mars 1999 published by elsevier science b v all rights reserved

the history of allan hills 84001 revised multiple shock events the geologic history of martian meteorite allan hills alh 84001 is more complex than previously recognized with evidence for four or five crater forming impacts onto mars this history of repeated deformation and shock metamorphism appears to weaken some arguments that have been offered for and against the hypothesis of ancient martian life in alh 84001 allan hills 84001 formed originally from basaltic magma its first impact event i1 is inferred from the deformation d1 that produced the granular textured bands crush zones that transect the original igneous fabric deformation d1 is characterized by intense shear and may represent excavation or rebound flow of rock beneath a large impact crater an intense thermal metamorphism followed d1 and may be related to it the next impact i2 produced fractures fr2 in which carbonate pancakes were deposited and produced feldspathic glass from some of the igneous feldspars and silica after i2 carbonate pancakes and globules were deposited in fr2 fractures and replaced feldspathic glass and possibly crystalline silicates next feldspars feldspathic glass and possibly some carbonates were mobilized and melted in the third impact i3 microfaulting intense fracturing and shear are also associated with i3 in the fourth impact i4 the rock was fractured and deformed without significant heating which permitted remnant magnetization directions to vary across fracture surfaces finally alh 84001 was ejected from mars in event i5 which could be identical to i4 this history of multiple impacts is consistent with the photogeology of the martian highlands and may help resolve some apparent contradictions among recent results on alh 84001 for example the submicron rounded magnetite grains in the carbonate globules could be contemporaneous with carbonate deposition whereas the elongate magnetite grains epitaxial on carbonates could be ascribed to vapor phase deposition during i3

sulfur isotopic systematics in alteration assemblages in martian meteorite allan hills 84001 abstract alh84001 is a coarse grained clastic orthopyroxenite meteorite related to the snc meteorite group s hergottites n akhlites c hassigny superimposed upon the orthopyroxene dominant igneous mineral assemblage is a hydrothermal signature this hydrothermal overprint consists of carbonate assemblages occurring in spheroidal aggregates and fine grained carbonate sulfide vug filling the sulfide in this assemblage has been identified as pyrite an unusual sulfide in meteorites previously burgess et al 1989 reported a bulk 34 s for a snc group meteorite shergotty of 0 5 1 5 here we report the first martian 34 s values from individual sulfide grains using newly developed ion microprobe techniques we were able to determine 34 s of the pyrite in alh84001 with a 1 a precision of better than 0 5 the 34 s values for the pyrite range from 4 8 to 7 8 within the stated uncertainties the pyrite from alh84001 exhibits a real variability in 34 s in this alteration assemblage in addition these sulfides are demonstrably enriched in 34 s relative to canon diablo troilite and sulfides from most other meteorites this signature implies that the planetary body represented by alh84001 experienced processes capable of fractionating sulphur isotopes and that hydrothermal conditions changed during pyrite precipitation t ph fluid composition etc the fractionated signature of the sulphur in the pyrite is most likely attributed to either conditions of pyrite precipitation low temperature reduced low f o 2 and moderately alkaline ph 8 environment or enrichment of fluids in 34 s by surface processes weathering or impact processes prior to precipitation these new data are not consistent with the pyrite recording either biogenic activity or atmospheric fractionation of sulphur through nonthermal escape mechanisms or oxidation processes this study also demonstrates the usefulness of ion microprobe measurements of sulphur isotopes in constraining conditions on other planetary bodies

evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater evidence for perchlorates at rocknest

late pleistocene and holocene vegetation and climate records from lake kotokel central baikal region abstract climatically driven late pleistocene and holocene vegetation changes were reconstructed based on pollen records from the sediments of lake kotokel and cheremushka bog located on the eastern shore of lake baikal the described paleoenvironmental record has higher resolution than records collected from lake baikal and unites individual events identified in prior studies of bottom and onshore cores remarkable shifts in landscapes and expansions of index plants are as follows forest tundra and or forest steppe landscape with birch spruce artemisia and poaceae prevailed at ca 50 25 14 c kyr bp tundra and or steppe vegetation dominated by artemisia and poaceae was typical for the last glacial maximum the expansion of shrub birch and willow occurred at ca 15 5 14 c kyr bp two peaks of spruce expansion at ca 47 5 42 4 14 c kyr bp karginian time and at ca 14 5 13 ka bolling allerod warm intervals suggest that the condition were more humid than today a slight increase in artemisia at ca 11 10 5 14 c kyr bp 13 12 ka was indicative of the younger dryas event an expansion of birch forests with fir at ca 12 6 4 ka suggests higher humidity the currently dominant scots and siberian pine forests with birch expanded since 6 4 ka

s nc multiple source areas for martian meteorites the shergottite nakhlite and chassigny snc meteorites are igneous rocks from mars inferred previously to have been propelled into space and to earth by a single impact event however the sum of petrologic chemical and chronological data suggests two distinct sites of origin s from one nc from another differences between the s and nc include distributions of terrestrial residence ages cosmic ray exposure ages impact shock effects preterrestrial aqueous alteration products bulk magma compositions trace element magma chemistries and mantle source compositions if the s and nc did not come from the same site on mars selection criteria for determining source craters are relaxed and a number of craters become candidate sources formation of two meteorite source craters on young martian surfaces 1300 ma within the last 20 m y spanning the cosmic ray exposure ages seems to require either smaller source craters or greater cratering rates than allowed in current theories both of these options suggest that meteorites from nonvolcanic and ancient martian surfaces ought to be more common than the known types of martian meteorites the absence of such meteorites may reflect the physical properties of nonvolcanic and ancient surfaces or a failure to recognize these rock types as meteorites the alh84001 meteorite long classified as a diogenite may be such a sample of the ancient martian crust

textural maturity of cumulates a record of chamber filling liquidus assemblage cooling rate and large scale convection in mafic layered intrusions textural maturity describes the extent to which a rock has evolved from the initial reaction controlled texture towards textural equilibrium controlled by the minimization of interfacial energy solidification in a magma chamber results in the formation of an impingement texture by the random juxtaposition of planar sided grains orthocumulates in which the initial melt filled pores are pseudomorphed by later crystallizing phases have an ophitic or intersertal texture immediately after complete solidification which then evolves towards solid state equilibrium by rounding of initially planar grain boundaries and an increase in the median dihedral angle subtended at the junctions of two primocrystic grains with the interstitial phase the bulk of the increase in angle occurs just below the solidus temperature in kilometre scale mafic plutons quantification of textural maturity via measurement of dihedral angle populations in troctolitic and gabbroic cumulates from the rum eastern layered intrusion and the skaergaard intrusion demonstrates that the rocks preserve a record of thermal events related to magma chamber replenishment and the onset of chamber wide convection textural maturity is also a function of the liquidus phase assemblage for systems in which only olivine and plagioclase are liquidus i e cumulus phases in the main magma body above the crystal mush the texture is significantly less mature than that in systems in which clinopyroxene is an additional liquidus phase the difference in textural maturity reflects differences in the cooling and solidification rate and demonstrates directly that the liquidus phase assemblage plays a role in determining the thermal history of plutons

origin of carbonate magnetite sulfide assemblages in martian meteorite alh84001 a review of the mineralogical isotopic and chemical properties of the carbonates and associated submicrometer iron oxides and sulfides in martian meteorite alh84001 provides minimal evidence for microbial activity some magnetites resemble those formed by magnetotactic microorganisms but cubic crystals 50 nm in size and elongated grains 25 nm long are too small to be single domain magnets and are probably abiogenic magnetites with shapes that are clearly unique to magnetotactic bacteria appear to be absent in alh84001 magnetosomes have not been reported in plutonic rocks and are unlikely to have been transported in fluids through fractures and uniformly deposited where abiogenic magnetite was forming epitaxially on carbonate submicrometer sulfides and magnetites probably formed during shock heating carbonates have correlated variations in ca mg and 18o 16o magnetite rich rims and they appear to be embedded in pyroxene and plagioclase glass carbonates with these features have not been identified in carbonaceous chondrites and terrestrial rocks suggesting that the alh84001 carbonates have a unique origin carbonates and hydrated minerals in alh84001 like secondary phases in other martian meteorites have o and h isotopic ratios favoring formation from fluids that exchanged with the martian atmosphere i propose that carbonates originally formed in alh84001 from aqueous fluids and were subsequently shock heated and vaporized the original carbonates were probably dolomite magnesite siderite assemblages that formed in pores at interstitial sites with minor sulfate chloride and phyllosilicates these phases like many other volatile rich phases in martian meteorites may have formed as evaporite deposits from intermittent floods