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 microbes in early neoproterozoic stromatolites abstract the biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin this has particularly been the case with older precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics in some cases however evidence has been preserved through very early mineralisation precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms this study provides evidence from early neoproterozoic columnar stromatolites in the jiuliqiao formation from the southeastern margin of the north china platform for fossilized extracellular polymeric substances eps and cyanobacteria along with nanospheres which may represent permineralised viruses or viral like particles a similar chemical composition and colour along with their embedded and cross cutting relationships with the matrix suggest they are syn depositional products and not modern artefacts or the result of sample preparation the interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping baffling and binding processes the presence of virus like particles and mineralized eps with anhedral fine grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation this study demonstrates the use of a high definition scanning electron microscope to detect fossilized calcified filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis

a 56 million year rhythm in north american sedimentation during the phanerozoic abstract long term 10 myr fluctuations in climate sea level and sedimentation have been documented in the stratigraphic record but the lack of well constrained data series has made it difficult to rigorously evaluate cyclic periodic or quasi periodic changes at this scale here we utilize a new compilation of the coverage area of sedimentary rocks in north america to investigate the dominant modes orders of stratigraphic variability and to evaluate potential long period cyclic changes in sedimentation on the continent during the phanerozoic our analysis resolves two principal temporal modes of variability 1 a strongly sinusoidal mode with a periodicity of 56 myr 3 myr and 2 a longer term phanerozoic mode the m curve linked to the wilson cycle which is indistinguishable from a stochastic autoregressive process the newly identified 56 myr cycle in sedimentation delineates most of the cratonic sequences that have previously been identified qualitatively in north america but here we propose a quantitative redefinition that includes nine distinct units and two mega sequences the timing of the 56 myr beat in sedimentation is consistent with an orogenic oscillator source or an oscillatory dynamic in mantle convection and its tempo is statistically similar to a known rhythm in number of marine animal genera in the global fossil record thus the identification of a significant periodic signal in the sedimentary record of north america provides new evidence for an important tectonic and or mantle scale cyclic process that links both large scale biological evolution and physical environmental change

syndepositional cements associated with nannofossils in the marmolada massif evidences of microbially mediated primary marine cements middle triassic dolomites italy the marmolada platform is characterized by striking globose masses evinosponges arranged in concentric bands of fibrous calcite cements ranging in size from centimeters to several decimeters the lithogenetic importance of these peculiar cements has been recognized in many middle triassic buildups of the western tethys eds microanalyses revealed that these fibrous cements contain 1 3 mol of mg and detectable amounts of sr over 1000 ppm sometimes exceeding 10 000 ppm the strontium geochemical signature in neomorphic calcite could reflect the replacement of an aragonitic carbonate precursor the boundaries between the fibrous calcite bands are marked by alignments of microcrystalline aggregates of fluorapatite and or dolomite the presence of fluorapatite may indicate a depositional microenvironment eutrophic or rich in microbial communities epifluorescence analyses showed bright bands alternated to dark ones confirming that organic matter remains occur within the studied cements and could have played a significant role in supporting the widespread syndepositional cementation high magnification sem observations on bright epifluorescent bands showed the presence of widespread more or less spherical bodies ranging in size 100 300 nm these bodies could represent the relicts of nannobacterial cells

the late messinian event a worldwide tectonic revolution a review of geological and geophysical observations points towards a worldwide kinematic change at around 6 ma the synchronicity of many manifestations tectonics magmatism kinematics ecological events among others at 6 ma similar to those recognized from time to time on the geological time scale argues for a global geodynamic event that has led to many regional consequences on earth s surface in particular we propose that this global event was the main trigger for the three fold increase in sediment deposits in the world ocean over the last 5 ma but also for the onset of the messinian salinity crisis in the mediterranean area one of the most severe ecological crises in the earth s history we suggest this messinian revolution to be the last occurrence of cyclic successions of global events

interaction of rising and sinking mantle plumes the frequency of plume formation in fully developed thermal convection is determined experimentally because the fluid has a temperature dependent viscosity the cold and hot thermal boundary layers have different thicknesses and viscosities as a result plumes are released from these layers with different frequencies there also appears to be a direct temporal interaction between the cold and hot boundary layers in particular whereas there is a single frequency for cold plume formation hot plumes form with multiple frequencies one of which is similar to the frequency of cold plumes the measurements thus suggest that cold sinking plumes may induce hot rising plumes

time series analysis of large igneous provinces 3500 ma to present abstract we outline an efficient integrated wavelet a spectral and a cross spectral approach for the time series analysis of geologic data here these techniques are applied to a database of 154 large igneous provinces lips in order to test for cycles trends and abrupt changes in temporal distribution since 3500 ma the average frequency of events is relatively constant and supports an overall model of semicontinuous temporal emplacement of lips however several weak cycles were obtained in the analysis those of longest duration are a 170 m yr cycle from 1600 ma to present and in the late archean a 330 m yr cycle from about 3000 to 1000 ma a cycle decreasing in length from 730 to 550 m yr over the interval 3500 ma to present and a still weaker cycle increasing from 900 to 1000 m yr over the interval 2000 ma to present additional cycles of shorter duration include a 250 m yr cycle in the late archean a 230 m yr cycle in the phanerozoic a 105 m yr cycle in the early proterozoic an

sediment cycling on continental and oceanic crust sedimentary rocks are often described as declining in quantity with increasing age due to the cumulative effects of crustal deformation and erosion one important implication of such a model is that the geological record becomes progressively less voluminous and less complete with increasing age here we show that the predictions of a model in which the destruction of sedimentary rock is the predominant process signal are borne out only among sediments deposited on oceanic crust and among sediments deposited above sea level in non marine environments most of the surviving volume of sedimentary rock 75 was deposited in and adjacent to shallow seas on continental crust and does not exhibit any steady decrease in quantity with increasing age instead shallow marine sediments exhibit large fluctuations in quantity that were driven by shifting global tectonic boundary conditions such as those that occur during the breakup and coalescence of supercontinents the accumulation of sediments on the continents has not been uniform in rate but it does record a primary signal of net growth that has many implications for the long term evolution of earth s surface environment

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

on the relationship between macrostratigraphy and geological processes quantitative information capture and sampling robustness abstract spatial and temporal patterns in the sedimentary record are controlled by a wide range of forcing mechanisms macrostratigraphy uses the temporal ranges of gap bound rock packages compiled separately for different geographic locations to quantify these patterns the total number of gap bound packages d and the rates of package initiation and truncation p and q respectively distill depositional geometries into time series that preserve information on both the spatial extent and the temporal continuity of deposition these macrostratigraphic quantities should in principle relate quantitatively to the underlying forcing mechanisms that govern sedimentation here we use a numerical model of continental margin sedimentation to test the extent to which time varying forcing mechanisms including subsidence sediment supply and sea level change can be detected quantitatively by the application of macrostratigraphy spectral and information theoretic analyses of time series of d p and q show

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

quaternary phosphorites from the continental margin off chennai southeast india analogs of ancient phosphate stromatolites abstract pleistocene phosphorites occur on the continental margin off chennai abundantly in the depth range of 186 293 m they are associated with outer shelf glauconites and carbonate skeletals including large shells of molluscs and rhodoliths these are primary phosphate deposits and are similar to phosphate stratiform stromatolites this is the first report of phosphate stratiform stromatolites during the quaternary and modern times and they provide a quaternary analog for ancient phosphorites thin sections of phosphorites exhibit laminated phosphatized microbial mats consisting of mechanically deposited clastic particles or of phosphatic molds clay particles are scattered throughout the matrix sem studies reveal that the laminated phosphate matrix is made of thin sheets of tightly packed apatite globules densely packed intertwined microfilaments or filament molds phosphate with obscured laminae is composed of phosphate tubules cell like structures resembling coccoid cyanobacteria or their botryoidal aggregates are common carbonate fluorapatite and low magnesium and high magnesium calcites are the major mineral phases the structural co2 content of apatite ranges from 4 to 5 5 quartz feldspar and goethite are accessory minerals the microbial mats were formed on the outer shelf most probably during conditions of low sea level in the quaternary and microbial processes played a major role in direct phosphatization of these mats the primary phosphorus source seems to have been the continental supply and degradation of organic matter associated with benthic microbial communities the phosphate stratiform stromatolites thus formed were subsequently reworked into a shelf margin depression and resulted in the occurrence of condensed phosphorites

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

an 60 million year periodicity is common to marine 87sr 86sr fossil biodiversity and large scale sedimentation what does the periodicity reflect abstractwe find that the marine 87sr 86sr record shows a significant periodicity of m yr the 87sr 86sr record is out of phase with a 62 3 m yr periodicity previously reported in the record of marine animal diversity these periodicities are close to 58 4 m yr cycles found for the number of gap bounded sedimentary carbonate packages of north america we propose that these periodicities reflect the operation of a periodic pulse of the earth in large scale earth processes these may be linked to mantle or plate tectonic events possibly uplift which affects the earth s climate and oceans and thus the geochemistry sedimentation and biodiversity of the marine realm

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

the rise and fall of stromatolites in shallow marine environments stromatolites are abundant in shallow marine sediments deposited before the evolution of animals but in the modern ocean they are restricted to locations where the activity of animals is limited overall decline in the abundance of stromatolites has therefore been attributed to the evolution of substrate modifying metazoans with phanerozoic stromatolite resurgences attributed to the aftermaths of mass extinctions here we use a comprehensive stratigraphic database the published literature and a machine reading system to show that the rock record normalized occurrence of stromatolites in marine environments in north america exhibits three phases an initial paleoproterozoic ca 2500 ma increase a sustained interval of dominance during the proterozoic 2500 800 ma and a late neoproterozoic 700 541 ma decline to lower mean prevalence during the phanerozoic 541 0 ma stromatolites continued to exhibit large changes in prevalence after the evolution of metazoans and they transiently achieved proterozoic like prevalence during the paleozoic the aftermaths of major mass extinctions are not well correlated with stromatolite resurgence instead stromatolite occurrence is well predicted by the prevalence of dolomite a shift in carbonate mineralogy that is sensitive to changes in water column and pore water chemistry occurring during continent scale marine transgressive regressive cycles

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

a genetic link between konzentrat and konservat lagerstatten in the fezouata shale lower ordovician morocco abstract in the central anti atlas morocco zagora region the fezouata shale has yielded an extraordinary fossil lagerstatte documenting the initial stages of the great ordovician biodiversification event this lagerstatte contains abundant and exceptionally well preserved fossils epf exhibiting soft bodied preservation as well as hard mineralized parts of extinct organisms while soft bodied preservation in the fezouata shale is confined to a few stratigraphic intervals other fossiliferous intervals contain only shelly fossils in sandstone lenses sl placed in the context of a previously established depositional model epf are interpreted as autochthonous assemblages buried by storm deposits close to storm wave base there the current component of storms is reduced compared to proximal settings and weak oscillation is dominant resulting in the record of oscillation ripples in contrast bioclastic accumulations were generated upslope in shallower more proximal lower shoreface environments there the current component of storms was significant as suggested by the disarticulation of skeletal remains bioclastic materials are localized in sl which are lenses a few tens of centimeters in thickness and a few meters in width and length these lenses commonly display erosive bases and convex tops resulting in a lobate or a channel lobe morphology a large amount of sediment was thus rapidly deposited resulting in the rapid burial of allochthonous material across a strongly localized surface of the sea floor integrating both sedimentological and paleontological evidence intervals yielding epf are considered as konservat lagerstatten ksl in contrast with bioclastic accumulations defined as konzentrat lagerstatten kzl thus ksl assemblages are interpreted to approximate biocenoses in which organisms experienced rapid burial by distal tempestites while kzl assemblages more likely correspond to thanatocenoses locally deposited by storm back currents here a genetic link between ksl and kzl is suggested within the fezouata shale both types of lagerstatten were related to storm activity but at different depths

marine diversity in the geological record and its relationship to surviving bedrock area lithofacies diversity and original marine shelf area biological principles suggest that recorded species diversity should increase as sampled area and habitat diversity increase however the interactions between earth system drivers of these physical quantities their representation in the preserved rock record and fossil species counts are debated we tracked marine bedrock area lithofacies diversity and echinoid species diversity through an 80 m y sea level cycle as recorded in the cretaceous of the united kingdom to test these relationships relative completeness of the rock record rises during transgression but drops rapidly at maximum flooding and continues to fall during highstand lithofacies diversity peaks during transgression but drops sharply as maximum flooding is reached whereas bedrock area peaks at maximum flooding then declines progressively through the highstand interval as a result of post cretaceous erosion both bedrock area and number of lithofacies units correlate with species diversity but species diversity is predicted best by the two combined there are no simple relationships between bedrock area and lithofacies diversity or the original area of marine sediments and range of habitats that once existed these variables are strongly shaped by stratigraphic architecture while the geological record left by a major sea level cycle accurately captures the biological evolution of local communities it is incomplete and systematically biased in its coverage of environments and communities erosional truncation of sediment packages and species ranges in the later stages of sea level cycles explains the reported asymmetric relationship between macroevolution and macrostratigraphy

alternative origins for nannobacteria like objects in calcite more than 40 calcite precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical rod and ovoid shaped objects that have been widely interpreted as evidence of nanometer scale life i e nannobacteria individual experiments included the addition of soluble organic compounds common species of eubacteria or phage induced eubacterial lysates these experiments indicate that many of the nanometer scale objects have inorganic or nonnannobacterial origins in the precipitation experiments calcite formed euhedral crystals 50 800 nm in diameter and smaller 50 nm anhedral or rounded particles or protocrystals the small anhedral or rounded solids resembled nannobacteria the relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component these controlled experiments are in accord with observations that rounded nanometer scale objects are more common in minerals formed in organic rich environments bacterial fragments occur as rounded to irregularly shaped particles that included cell wall fragments expulsed cytoplasm and relict capsules that also closely resembled nannobacteria acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer scale features that resembled nannobacteria in natural carbonates the shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching much caution is advisable in interpreting the origin of rounded features 50 nm

sea level cycles during the growth of atlantic type oceans abstract first order changes in global sea level are commonly thought to be the result of short term fluctuations in oceanic spreading rate however eustatic high stands have occurred only twice in phanerozoic time and in both cases have followed supercontinent break up by a lag period of 50 100 ma therefore if pulses in spreading rate were the primary control of eustasy then for some reason rate increases would have had to have occurred with predictable periodicity with respect to major rifting events alternatively we propose that the major control on first order sea level cycles is the formation of atlantic type oceans with its attendant changes in the area age distribution of the global ocean floor and the formation of extensional passive margins our calculations indicate that both the approximate magnitude and relative timing of sea level highstands relative to supercontinent break up are predicted by this mechanism thus the importance of short term spreading rate variations in eustatic cycles becomes secondary

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

links between eccentricity forcing and the 100 000 year glacial cycle the 100 000 year glacial cycles are generally thought to be driven by the eccentricity of the earth s orbit statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100 000 year eccentricity cycle variations in the eccentricity 100 000 yr obliquity 41 000 yr and precession 23 000 yr of earth s orbit have been linked to glacial interglacial climate cycles it is generally thought that the 100 000 yr glacial cycles of the past 800 000 yr are a result of orbital eccentricity1 2 3 4 however the eccentricity cycle produces negligible 100 kyr power in seasonal or mean annual insolation although it does modulate the amplitude of the precession cycle alternatively it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle5 6 7 here i use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100 000 yr glacial cycles using cross wavelet phase analysis i show that the relative phase of eccentricity and glacial cycles has been stable since 1 2 myr ago supporting the hypothesis that 100 000 yr glacial cycles are paced8 9 10 by eccentricity4 11 however i find that the time dependent 100 000 yr power of eccentricity has been anticorrelated with that of climate since 5 myr ago with strong eccentricity forcing associated with weaker power in the 100 000 yr glacial cycle i propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing which disrupts the internal climate feedbacks that drive the 100 000 yr glacial cycle this supports the hypothesis that internally driven climate feedbacks are the source of the 100 000 yr climate variations12

microbially influenced formation of 2 724 million year old stromatolites nanoscale evidence suggests that the tumbiana formation stromatolites in australia were influenced by microbial activity in the stromatolites clusters of organic globules are closely associated with 2 724 million year old aragonite crystals