reply to the comments of d l pinti r mineau and v clement and of a o marshall and c p marshall on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 abstract the abundant and diverse assemblage of filamentous microbial fossils permineralized in the 3465 ma apex chert of northwestern australia among the oldest records of life are arguably the best studied by the most workers using the most advanced techniques in the history of science despite the extensive body of data establishing the biogenicity of the demonstrably cellular carbonaceous apex fossils pinti et al 2013 and marshall and marshall 2013 have raised issues regarding the interpretation of their studies of the apex chert presented in our recent review article schopf and kudryavtsev 2012 we agree with the assessment of both of the relevant papers by pinti et al 2009 2013 the observations they report do not apply to the bona fide microscopic fossils of the apex chert similarly like the minute objects reported by pinti et al 2009 2013 the quartz and haematite filled fractures discussed by marshall and marshall 2013 are mineralic pseudofossils that are not relevant to interpretation of the apex fossil microbes and their suggestion that multiple populations of carbonaceous material may be a wide spread issue through out the precambrian is without merit

modeling the radio echo reflections inside the ice sheet at summit greenland 1 radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice to increase our understanding of these internal reflections we have used synthetic seismogram techniques from early seismic modeling to construct two models both models were one dimensional the first considered only primary reflections while the second included both primary and multiple reflections the inputs to both models were a radio pulse and data from the greenland ice core project grip core of length 3028 m the ice core data consisted of a profile of the high frequency conductivity calculated from dielectric profile dep measurements and a smooth profile of the real permittivity the models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two way travel time both models gave similar results indicating that multiples do not alter the travel time of the reflections i e no o doherty anstey effect at our time resolution one of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace the processed result contained many of the larger reflections recorded below about 500 m including nearly all the features from depths greater than 1500 m in particular several interstadial events in the wisconsin age ice since high frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet it is possible to conclude that the reflections deep inside the greenland ice sheet can be treated as isochrons

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

basal melting at the ekstrom ice shelf antarctica estimated from mass flux divergence we characterize the basal mass balance of the ekstr om ice shelf dronning maud land antarctica using interferometrically derived surface velocities and ice thickness measurements from radio echo sounding res the surface velocities are based on data from european remote sensing satellites 1 and 2 ers 1 2 during 1994 97 the ice thickness grid consists of 136 res profiles acquired between 1996 and 2006 mass fluxes are calculated along selected res profiles where possible to reduce uncertainties from ice thickness interpolation elsewhere large scale mass fluxes are calculated using interpolated ice thickness data themass flux into the ekstr om ice shelf from themain grounded drainage basins is estimated to be 3 19 0 4gt a 1 the mass flux near the ice shelf front is 2 67 0 3gt a 1 assuming steady state and based on the equation of continuity we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting refreezing using net snow accumulation rates from previous studies we link the mass flux divergence in irregular shaped polygons to processes beneath the ice shelf the highest subglacial melt rates of 1 1ma 1 are found near the grounding zone of two main inflow glaciers and around the german station neumayer iii the detection of unlikely refreezing in a small area 15 km west of neumayer iii is attributed to both dataset inaccuracies and a possibly past violation of the steady state assumption in general the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies

verification of velocity resistivity relationships derived from structural joint inversion with borehole data we present results of three dimensional joint inversion of seismic magnetotelluric and gravity data over a marine salt dome such structures are difficult to image with a single method and our results demonstrate how combining different techniques can yield improved results more importantly we examine the reliability of velocity conductivity relationships derived from structure coupled joint inversion approaches comparison with a seismic reflection section shows that our models match the upper limit of the salt furthermore velocity and resistivity logs from a borehole drilled into the salt dome s flank match within error those recovered by the inversion the good match suggests that the difference in length scale does not have a significant effect in this case this provides a strong incentive to incorporate borehole data into the joint inversion in the future and substantiates approaches that use the relationships derived from joint inversion models for lithological classification

biogenicity of earth s earliest fossils a resolution of the controversy abstract the abundant and diverse assemblage of filamentous microbial fossils and associated organic matter permineralized in the 3465 ma apex chert of northwestern australia widely regarded as among the oldest records of life have been investigated intensively first reported in 1987 and formally described in 1992 and 1993 the biogenicity of the apex fossils was questioned in 2002 and in three subsequent reports however as is shown here by use of analytical techniques unavailable twenty years ago the apex filaments are now established to be bona fide fossil microbes composed of three dimensionally cylindrical organic kerogenous walled cells backed by a large body of supporting evidence of similar age other microfossils stromatolites and carbon isotopic data it seems clear that microbial life was present and flourishing on the early earth 3500 ma ago

hydrothermal alteration and microfossil artefacts of the 3 465 million year old apex chert the earliest fossils of cyanobacteria have been controversially reported from the 3 465 million year old apex chert in western australia mineralogical analyses of the rock near the fossil site indicate that the site experienced repeated alterations at low and medium temperatures and is therefore unlikely to have preserved any early forms of life the 3 465 million year old apex chert of the pilbara craton in western australia has been controversially reported to contain some of the oldest fossil evidence for life tiny carbonaceous filaments interpreted as cyanobacteria1 yet on the basis of the presence of barite and native metals it has been suggested that the chert formed from hydrothermal fluids at temperatures greater than 250 c refs 2 3 an unlikely environment for cyanobacteria here we use scanning electron microscopy to assess the mineralogy and depositional setting of the chert veins surrounding the nodes that contain the microfossils in addition to rare native metals we find an assemblage of iron oxides and clay minerals which we interpret to have formed during repeated pulses of hydrothermal alteration at low to medium temperatures we also find micrometre sized silica structures that resemble microbial exopolymers4 and textures formed by the partial dissolution of tubular minerals that look similar to fossilized microbial mats5 other branched microstructures suggest post depositional colonization of microcracks and fissures by microbes5 these observations are not directly applicable to the carbonaceous filaments purported to be the earliest fossil evidence of life as we did not recover any in our sample however because of the observed hydrothermal and groundwater alteration we conclude that the apex chert is unlikely to have preserved any early forms of life

airborne thickness and freeboard measurements over the mcmurdo ice shelf antarctica and implications for ice density 1 we present airborne measurements to investigate the thickness of the western mcmurdo ice shelf in the western ross sea antarctica because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area in november 2009 we used a helicopter borne laser and electromagnetic induction sounder em bird to measure several thickness and freeboard profiles across the ice shelf the maximum electromagnetically detectable ice thickness was about 55 m assuming hydrostatic equilibrium the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m 3 densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer the equivalent thickness of debris at a density of 2800 kg m 3 is found to be up to about 2 m thick a subice platelet layer below the ice shelf similar to what is observed in front of the ice shelf below the sea ice is likely to exist in areas of highest thickness the thickness and density distribution reflects a picture of areas of basal freezing and supercooled ice shelf water emerging from below the central ice shelf cavity into mcmurdo sound

early biosphere magnifying ancient microstructures purported 3 465 million year old microfossils from australia have been the subject of considerable debate a method to distinguish between pristine fossils mineral artefacts and subsequent microbial contamination will aid the search for ancient biogenic material

new maps of the ice thickness and subglacial topography in dronning maud land antarctica determined by means of airborne radio echo sounding since the austral summer 1994 95 the alfred wegener institute awi hascarried out airborne radio echo sounding measurements res in antarctica withits newly designed res system since 1995 96 an ongoing presite survey foran ice coring drill site in dronning maud land dml has been carried out this survey is part of the epica programme european project for ice coring inantarctica it covers an area of 948000 km2 with more than 49500 km ofairborne res obtained from more than 200 hours of flight operation flown from1994 1997 within this paper first results of the airborne res survey will begraphically summarized as newly derived maps of the ice thickness and thesubglacial topography as well as a 3d view of surface and subglacial bed andoutcrop topography revealing a total icevolume of 1 48 million km3

geometry and thermal regime of the king george island ice cap antarctica from gpr and gps king george island is the largest of the south shetland islands close to the tip of the antarctic peninsula the annual mean temperature on the island has increased by 1 c during the past three decades and the ice cap that covers the majority of the island is sensitive to climatic change we present data from two field campaigns 1997 and 2007 700 km of global positioning system gps and ground penetrating radar gpr profiles were collected on arctowski icefield and on the adjacent central part the data were analysed to determine the surface and bed topography and the thermal regime of the ice average ice thickness is 250 m and maximum thickness is 420 m the gpr profiles show isochrones throughout the ice cap which depict the uparching of raymond bumps beneath or close to the ice divides a water table from percolation of meltwater in the snowpack shows the firn ice boundary at 35 m depth the firn layer may be temperate due to the release of latent heat in the area below 400 m a s l backscatter by water inclusions is abundant for ice depths below the water table we interpret this as evidence for temperate ice scatter decreases significantly above 400 m ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations

distribution of marine ice beneath the amery ice shelf we present a map of the marine ice accreted to the base of the amery ice shelf ais east antarctica this map is obtained by converting a digital elevation model dem of the ais generated from satellite radar altimeter data to an ice thickness map assuming hydrostatic equilibrium and subtracting from that a second ice thickness map derived from airborne radio echo sounding res measurements the res signal does not penetrate the marine ice so the measurement is only to the meteoric marine ice boundary and therefore the difference between the two maps is the marine ice thickness the marine ice is up to 190 m thick and accounts for about 9 of the shelf volume it is concentrated in the northwest of the shelf a result of the clockwise ocean circulation in the cavity below

ground penetrating radar profiles of the mcmurdo shear zone antarctica acquired with an unmanned rover interpretation of crevasses fractures and folds within firn and marine ice abstractthe crevassed firn of the mcmurdo shear zone sz within the ross ice shelf may also contain crevasses deep within its meteoric and marine ice but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically we used a lightweight robotic vehicle to tow 200 and 400 mhz ground penetrating radar antennas simultaneously along 100 parallel transects over a 28 km2 grid spanning the sz width transects were generally orthogonal to the ice flow total firn and meteoric ice thickness was approximately 160 m firn crevasses profiled at 400 mhz were up to 16 m wide under snow bridges up to 10 m thick and with strikes near 35 40 to the transect direction from the top down 200 mhz profiles revealed firn diffractions originating to a depth of approximately 40 m no discernible structure within the meteoric ice a discontinuous transitional horizon and at least 20 m of stratified marine ice 28 31 m of freeboard found more marine ice exists based on 10 consecutiv

comment on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 recently schopf and kudryavtsev 2012 have published an exhaustive review on the biogenicity of the most controversial evidence of ancient life on earth to date an assemblage of carbonaceous filaments found in the 3465 ma apex chert of northwestern australia schopf and packer 1987 schopf 1993 the morphology of the filaments their carbon isotopic composition and the sedimentary environment interpreted as shallow marine suggested to schopf 1993 that these filaments were fossilized cyanobacteria this discovery sparkled a large controversy among the scientific community that lasted for more than 25 years see pinti and altermann 2011 for a review on the subject in the synopsis of the controversy page 762 schopf andkudryavtsev 2012 wrote the apex fossils have subsequently been suggested to be inorganic silica or clay mineral needle like crystals pinti et al 2009 again at page 769 the authors reported that needles composed of halloysite al2si2o5 oh 4 a clay mineral and of quartz sio2 have been compared with the apex fossils pinti et al 2009 these are two serious misstatements because we never compared any of the pseudofossils that we observed in apex chert to the microfossils of schopf 1993 schopf and kudryavtsev 2012 themselves report at

carbonaceous microstructures from sedimentary laminated chert within the 3 46 ga apex basalt chinaman creek locality pilbara western australia abstract hydrothermal black chert veins intruding the 3 46 ga apex basalt contain some of earth s oldest microfossil like objects whose biogenicity has been questioned whilst these black chert veins have been studied in great detail relatively little is known about the stratiform seafloor sedimentary cherts that are conformably interbedded with volcanic rocks of the apex basalt herein we document and assess the biogenicity of carbonaceous microstructures present in the lowermost of the stratiform chert units informally known as the apex chert at the chinaman creek locality in the marble bar greenstone belt pilbara craton western australia carbonaceous material mostly occurs within clotted grey black cherts and microgranular grainstone like cherts within the stratiform unit the latter being the major focus of this study in the clotted cherts carbon occurs as lobate fluffy grains rare compressed flakes and as a grain boundary phase around spherulitic silica there is no morphological evidence to support the biogenicity of these microstructures in contrast the microgranular chert contains fluffy and flaky carbonaceous grains plus laminated grains comprising multiple non isopachous wrinkled carbonaceous laminae with noted thickening towards some ridge crests as determined by confocal laser scanning microscopy roll up structures provide evidence of an initial plasticity interpreted to have formed via the tearing up and current induced plastic deformation of microbial mat fragments geochemical mapping using laser raman micro spectroscopy and nanosims respectively demonstrates the antiquity of the carbon and reveals a close correlation between carbon nitrogen and sometimes sulphur concentrated within dark brown to black laminae adjacent to microgranular zones are zones of more persistent carbonaceous undulose filament like laminae that entrain relict sediment grains these microstructures are directly comparable to a sub type of microbially induced sedimentary structure miss widely reported from younger siliciclastic sediments colonised by microbial biofilms the morphology and chemical composition of both the non isopachous laminated grains and the filament like laminae are consistent with a biological interpretation suggesting microscopic miss were present in the microgranular stratiform apex chert however the fact that neither macroscopic miss nor bona fide microfossils have yet been reported from this unit coupled with the proximity of these structures to active hydrothermal vents potentially discharging hot carbon rich fluids urges caution in such an interpretation the chinaman creek apex chert investigated here is one of at least five sedimentary laminated cherts within the apex basalt these horizons are promising targets in the search for biological activity within a dominantly volcanic archaean environment

complex network of channels beneath an antarctic ice shelf ice shelves play an important role in stabilizing the interior grounded ice of the large ice sheets the thinning of major ice shelves observed in recent years possibly in connection to warmer ocean waters coming into contact with the ice shelf base has focused attention on the ice ocean interface here we reveal a complex network of sub ice shelf channels under the fimbul ice shelf antarctica mapped using ground penetrating radar over a 100 km2 grid the channels are 300 500 m wide and 50 m high among the narrowest of any reported observing narrow channels beneath an ice shelf that is mainly surrounded by cold ocean waters with temperatures close to the surface freezing point shows that channelized basal melting is not restricted to rapidly melting ice shelves indicating that spatial melt patterns around antarctica are likely to vary on scales that are not yet incorporated in ice ocean models

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

radar detection of accreted ice over lake vostok antarctica abstract airborne radar data collected over lake vostok east antarctica show a reflection close to the vostok ice core below the depth of the meteoric accreted ice boundary maib and near the boundary between impurity rich 1 and impurity poor 2 accreted ice a12b the spatial pattern of detection of this reflection is aligned with ice flow over the southern half of the lake ice core data from the accreted ice show large variations in the number density of inclusions soluble chloride ion concentration cl charge balance derived acidity h cb and crystal orientation fabric here we investigate the existing hypothesis that this reflection is due to the maib and seek possible reflection causes that explain the radar derived reflectivity 51 8 db the likely maximum reflectivity due to an insoluble mineral inclusion contrast is 125 db if none of the cl or h ions are trapped within inclusions then ice conductivity models predict a reflectivity of 50 db near the maib and 58 db near the a12b both primarily due to large h cb changes if some of those ions are trapped within inclusions then those values are smaller fabric contrasts at either boundary can produce significant reflectivities 62 db these results indicate that the mineral inclusion contrast near the maib does not cause the observed reflection because of uncertainty in the in situ location of the soluble impurities and because impurity rich accreted ice 1 is believed to only originate in the small bay in the southwestern corner of the lake yet the reflection is observed over a much wider area we argue that a fabric contrast at the a12b is the probable reflection cause both predicted spatial variations in accretion rates near the upstream shoreline or lower ice temperatures along flowbands that originate at bedrock ridges near the upstream shoreline may explain why the reflection is not detected everywhere that accretion is predicted

haematite pseudomicrofossils present in the 3 5 billion year old apex chert microstructures from the 3 5 billion year old apex chert have been interpreted as the remains of ancient cyanobacteria geochemical analyses suggest similar structures at the same location are instead haematite filled fractures although carbonaceous material in the surrounding matrix is consistent with the presence of microbes at this time

structural characterization by raman hyperspectral mapping of organic carbon in the 3 46 billion year old apex chert western australia abstract the 3 46 billion years old apex chert pilbara craton western australia is well known for hosting the oldest highly disputed microfossils on earth this rock has a complex history of thermal alteration that includes circulation of hydrothermal fluids lower greenschist facies regional metamorphism and post metamorphic weathering by meteoric fluids carbonaceous material occurs in the sedimentary stratiform part of the chert as well as the underlying intruding hydrothermal black chert veins in order to identify a least altered remnant of early life it is necessary to develop a method that enables rapid evaluation of cm structural order on a small spatial scale here we present the detailed characterization of cm in the apex chert by raman hyperspectral mapping it is shown that this approach gives better estimates of average raman band ratios than individual point analyses and it is demonstrated that significant differences in structure exist between cm in the stratiform part of the apex chert and cm in an underlying black chert vein the large raman map based datasets also reveal that significant mixing took place between these two end members cm s indicating that the apex chert has been thoroughly altered by hydrothermal fluid circulation at the brecciated intersection between the stratiform chert and the intrusive hydrothermal chert vein very poorly ordered cm was found that is not in line with lower greenschist facies regional metamorphism it is speculated here that this cm represents an organic fraction that was introduced or thoroughly altered by late stage meteoric fluids alternatively the ubiquitous presence of hematite in this sample caused a perturbation in the raman spectra of the cm leading to an artifact in the calculated raman based band ratios overall it can be concluded that the best preserved cm occurs in the stratiform parts of the apex chert while earlier discussions on organic microfossils in this rock often focused on parts of the chert that either represented the hydrothermal veins or the brecciated intersection between the veins and the stratiform part

precambrian microbe like pseudofossils a promising solution to the problem of various problems that have hindered progress in documenting the precambrian history of life the difficulty in distinguishing between bona fide microbial fossils and nonbiological microscopic pseudofossils has been among the most serious though errors in the interpretation of putative precambrian fossil microbes have diminished greatly over recent years mistakes continue to be made we suggest that such errors can be avoided by the use of a multifaceted strategy based on a specified series of biologically definitive characteristics that document the presence of interrelated biological morphology and biologically derived chemistry to illustrate this promising approach we use optical microscopy confocal laser scanning microscopy and raman spectroscopy together to distinguish between authentic microbial fossils and microscopic look alikes both coccoidal and filamentous rock embedded in five proterozoic and two archean geological units bona fide fossils of the 800 ma bitter springs formation of central australia and 3050 ma farrel quartzite of northwestern australia and objects we regard to be pseudofossils from the 770 ma chanda limestone of southern india 800 ma myrtle springs formation of south australia 1020 ma lakhanda formation of southeastern siberia 1700 ma vempalle formation of central india and 2629 ma marra mamba iron formation of northwestern australia the results demonstrate that no single criterion by itself is sufficient to establish the biological origin of such objects instead as shown here this problem appears solvable by the use of an interdisciplinary approach that combines the data and techniques of geology biology and chemistry

seismic reflection studies of the amery ice shelf east antarctica delineating meteoric and marine ice summary a detailed seismic reflection survey has been performed utilizing a 24 channel spread with a 10 m geophone spacing giving a maximum fold coverage of six with the aim of revealing a detailed view of the subsurface structure of the amery ice shelf showing meteoric and marine ice thicknesses water column thickness and sediment structure the survey has successfully delineated the subhorizontal meteoric and marine ice layers with average thicknesses of 754 and 20 m respectively the water column is 595 m thick placing the seafloor at a depth of 1369 m below the ice surface a 55 m thick subhorizontally layered sedimentary unit can be seen below which are deep features at approximately 2225 m below the surface these features could reveal the presence of dykes a broken bedrock surface or glaciologically derived clasts that are sufficiently large enough to show up within the data