<p>Two missions are on Mars looking for traces of life (MSL and Mars 2020) while th... more <p>Two missions are on Mars looking for traces of life (MSL and Mars 2020) while the ExoMars mission, slated for launch later this year, is postponed. All missions are equipped with a powerful array of instrumentation for <em>in situ </em>analyses. In addition, the ExoMars rover, Rosalind Franklin, has the advantage of a 2 m drill to penetrate beneath the oxidised and UV-irradiated surface [1]. However, unless phototrophic life forms were able to develop on a planet that was never permanently habitable and that was characterised by punctuated and likely unconnected habitable niches [2, 3], martian life likely remained in a very primitive state of evolution, potentially similar to terrestrial chemotrophs, <em>i.e. </em>discrete, very small cells and colonies that leave even more subtle fossil remains. Indeed, only in the vicinity of nutrient-rich hydrothermal environments can chemotrophic biomass develop to create potentially visible morphological signatures in the form of a clotted texture in the associated sediments – a texture that is not immediately identifiable as a biosignature but that would warrant further analysis of such rocks by other instruments, such as SAM on Curiosity, SHERLOC on Perseverance, or MOMA on Rosalind Franklin.</p> <p>Taking the early terrestrial environment and early life as analogues for habitable environments and primitive life forms on early Mars, it is becoming clearer that the most primitive of life forms known on Earth, chemolithotrophs that obtain energy from oxidation of inorganic substrates (e.g. ferrous iron, hydrogen sulfide, elemental sulfur, thiosulfate, or ammonia), were widely distributed but, because of their very small size (< 1 µm diameter) and very small, heterogeneously distributed colonies (5 µm to some tens of microns), are typically undetectable through bulk analyses (bulk carbon contents are generally 0.01-0.05 %.) (Fig. 1). To compound the challenge, morphologically-recognisable cells are rarely observed, while degraded cells mixed with generic extracellular polymeric substances (EPS) are more frequent. Chemolithotrophs can inhabit sediment particle surfaces and pore space close to the surface or at depth, as long as they have access to nutrients and water. But how to identify them <em>in situ </em>on Mars? Even on Earth with well-equipped, state of the art laboratories, detection and identification of fossil chemolithotrophs is difficult and, often, controversial. The solution requires seeking to simultaneously detect structural information of the organisms’ presence and analyse well-preserved organogeochemical signature with spatial precisions on the order of a micron and detection limits as low as possible. This would be a challenge for Mars Sample Return in the near future.</p> <p><img src="" alt="" /></p> <p><strong>Figure 1. </strong>(A-C) distribution of tiny colonies and EPS clumps (red circles) in a silicified, volcanic sediment [3] at increasing magnifications. Individual dividing cells visible only at maximum resolution in (C).</p> <p><strong>References:</strong> [1] Vago, J.L., et al. (2017) <em>Astrobiology, </em>17: 471–510. [2] Cockell et al., 2012. <em>Icarus, </em>217:184–193. [3] Westall et al., (2015) <em>Astrobiology, </em>17: 998-1029. [4] Author J. et al. (2002) <em>LPS XXXIII</em>, #2110.</p>
The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The... more The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The detection of planets with a wide range of masses demonstrates that extra-solar planets of low mass exist. In this paper we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines including astrophysics, planetary sciences, chemistry and microbiology. Darwin is designed to detect and perform spectroscopic analysis of rocky planets similar to the Earth at mid-infrared wavelengths (6 to 20 µm), where an advantageous contrast ratio between star and planet occurs. The baseline mission lasts 5 years and consists of approximately 200 individual target stars. Among these, 25 to 50 planetary systems can be studied spectroscopically, searching for gases such as CO 2 , H 2 O, CH 4 and O 3. Many of the key technologies required for the construction of Darwin have already been demonstrated and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.
The oldest traces of life on Earth occur in cherts (silicified volcanic silts and sands) that wer... more The oldest traces of life on Earth occur in cherts (silicified volcanic silts and sands) that were deposited in coastal environments ∼3.5 billion years ago [1, 2, 3, 4, 5, 6]. These microfossils are the remains of relatively evolved organisms, implying that life had to have appeared much earlier [6]. However, studies related to the origin of life are hampered by the fact that suitable rocks dating from the first billion years are lacking on Earth, since older materials are too heavily metamorphosed or have been destroyed by plate tectonics. Investigations are now focussed on the search for older microfossils on other planets and, in particular, on Mars. Mars does not appear to have undergone plate tectonic activity as on Earth and, if life appeared on that planet, its fossilised traces could be found embedded in rocks from the
Similarities in the early histories of Mars and Earth suggest that life may have arisen on Mars a... more Similarities in the early histories of Mars and Earth suggest that life may have arisen on Mars as it did on Earth. The early life forms on Mars were probably simple organisms, similar to terrestrial prokaryotes. In fact, given the early deterioration of the Martian climate, it is unlikely that life on Mars could ever have reached more sophisticated evolution. Based on the present knowledge of Mars, the possibility of extant life at the surface is small. However, given the adaptability of terrestrial prokaryotes under adverse conditions, it is not excluded. Any extant life is hypothesized to reside in the permafrost in a dormant state until "reanimated" by impact-caused hydrothermal activity. Using this rationale, a group of European scientists worked together to conceive a hypothetical strategy to search for life on Mars. A possible configuration for a lander/rover is outlined.
Assessing the habitability of Mars and detecting life, if it was ever there, depends on knowledge... more Assessing the habitability of Mars and detecting life, if it was ever there, depends on knowledge of whether the combined environmental stresses experienced on Mars are compatible with life and whether a record of that life could ever be detected. Many combinations of Mars relevant stress factors, such as high radiation dose rates and high UV uences combined with high salt concentrations, and low water activity, have not been investigated. In particular, the response of anaerobic organisms to Mars-like stress factors and combinations thereof are not known. In the EC project MASE (Mars Analogues for Space Exploration) we address these limitations by characterising different Mars analogue environments on Earth, isolating microorganisms from these sites and exposing them to Mars relevant stress factors alone and in combination. We want to find out, if these bacteria respond in an additive or synergistic way and if they would be able to survive on Mars. So far, eight only distantly rela...
In this study, we demonstrate the usefulness of Raman spectroscopy, and in particular Raman mappi... more In this study, we demonstrate the usefulness of Raman spectroscopy, and in particular Raman mapping, as a very powerful tool for the study of both organic matter and minerals associated with silicified biological remains. Our investigations concern silicified organic matter, microorganisms and biological remains of various origins and ages, from the metacherts of Isua, Greenland, 3.8 Ga, to silicified wood from the Petrified Forest National Park, Arizona, USA, 225 Ma.
MOROCCO) INVESTIGATED BY HR-SEM AND TOF-SIMS: FOSSIL ANALOGUES OF MOA-SRB CONSORTIA? B. Cavalazzi... more MOROCCO) INVESTIGATED BY HR-SEM AND TOF-SIMS: FOSSIL ANALOGUES OF MOA-SRB CONSORTIA? B. Cavalazzi, R. Barbieri, G.G. Ori, F. Westall, S.L. Cady, S. Gennaro, A. Lui, R. Canteri, M. Bersani, P. Lazzeri and G. Pepponi, Centre de Biophysique Moléculaire, CNRS, Orléans, FRANCE, Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, ITALY, Int'l Research School of Planetary Sciences, Università d'Annunzio, ITALY, Department of Geology, Portland State University, OR, USA, Fondazione Bruno Kessler, Ricerca Scientifica e Tecnologica, Trento, ITALY.
The MASE (Mars Analogues for Space Exploration) [1] project is a four-year collaborative research... more The MASE (Mars Analogues for Space Exploration) [1] project is a four-year collaborative research project supported by the European Commission Seventh Framework Contract. The aim of the project is to understand how combined environmental stresses influence the habitability of a number of Mars analogue environments in Europe and beyond. Field sites sampled for MASE include deep subsurface salts at Boulby Mine in the UK, sulfidic springs In Germany and an acidic cold lake in lceland. Samples and isolates have also been provided to the project from acidic deep subsurface environments at the Rio Tinto in Spain as well as permafrost sites in Russian Siberia and northern Canada. Crucial to assessing the habitability of any environmental system to be used as an astrobiological analogue • whether for life in general or, as in this case, for anaerobic microorganisms • is a detailed understanding of their geological and physiochemical context [2, 3]. One of the key outcomes of the MASE projec...
The aim of this article is to provide the reader with an overview of the different possible scena... more The aim of this article is to provide the reader with an overview of the different possible scenarios for the emergence of life, to critically assess them and, according to the conclusions we reach, to analyze whether similar processes could have been conducive to independent origins of life on the several icy moons of the Solar System. Instead of directly proposing a concrete and unequivocal cradle of life on Earth, we focus on describing the different requirements that are arguably needed for the transition between non-life to life. We approach this topic from geological, biological, and chemical perspectives with the aim of providing answers in an integrative manner. We reflect upon the most prominent origins hypotheses and assess whether they match the aforementioned abiogenic requirements. Based on the conclusions extracted, we address whether the conditions for abiogenesis are/were met in any of the oceanic icy moons.
Enigmatic microorganisms and life in extreme …, 1999
... Pub 30, 73-90. Poinar, GO.(1992) Life in Amber, Stanford University Press, Stanford. ... Astr... more ... Pub 30, 73-90. Poinar, GO.(1992) Life in Amber, Stanford University Press, Stanford. ... Astract. Westall, F.(1997b) in C. Cosmovici, S. Bowyer and D. Werthimer (eds.) Astronomical and Biochemical Origins and the Search for Life in the Universe, Editori compositrici, Bolgna, pp. ...
... Andreazza g , E-mail The Corresponding Author , Frédéric Foucher a , Jan Toporski h , E-mail ... more ... Andreazza g , E-mail The Corresponding Author , Frédéric Foucher a , Jan Toporski h , E-mail The Corresponding Author , Andrea Jauss h , Volker Thiel i , E-mail The Corresponding Author , Gordon Southam j , E-mail The Corresponding Author , Lachlan MacLean j , Susan ...
A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B ... more A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B together over the interval 0-350 mbsf (0-9 m.y.). High-resolution carbonate and opal data from the cores were correlated with the calcium and silicon signals from the GST logging run in Hole 704B to identify missing and disturbed intervals in the cores. Paleomagnetic and biostratigraphic age boundaries were then transferred to the composite depth records to obtain an age model, and sedimentation rates were calculated by linear interpolation between datums. Algorithms relating measured dry-bulk density to carbonate content and depth were generated to produce predicted values of density for every sample. Accumulation rates of bulk, carbonate, opal, and terrigenous sediment components were then computed to generate a record of sediment deposition on the Meteor Rise that has a resolution of better than 200,000 yr for the period from 8.6 to 1.0 m.y. From 8.6 to 2.5 m.y., bulk-accumulation rates on the Meteor Rise averaged less than 2 g/cm 2 /1000 yr and were dominated by carbonate deposition. The first significant opal deposition (6.0 m.y.) punctuated a brief (less than 0.6 Ma) approach of the Polar Front Zone (PFZ) northward that heralded a period of increasing severity of periodic carbonate dissolution events (terrigenous maxima) that abruptly terminated at 4.8 m.y. (base of the Thvera Subchron), synchronous with the reflooding of the Mediterranean after the Messinian salinity crisis. From 4.8 to 2.5 m.y., carbonate again dominated deposition, and the PFZ was far south except during brief northward excursions bracketing 4.2-3.9, 3.3-2.9, and 2.8-2.7 m.y. At 2.5 m.y., all components of bulk-accumulation rates increased dramatically (up to 15 g/cm 2 /1000 yr), and by 2.4 m.y., a pattern of alternating, high-amplitude carbonate and opal cyclicity marked the initiation of rapid glacial to interglaciál swings in the position of the PFZ, synchronous with the "onset" of major Northern Hemisphere glaciation. Both mass-accumulation rates and the amplitude of the cycles decreased by about 2 m.y., but opal accumulation rates remained high up through the base of the Jaramillo (0.98 m.y.). From 1.9 to 1 m.y., the record is characterized by moderate amplitude fluctuations in carbonate and opal. This record of opal accumulation rates is interpreted as a long-term "Polar Front Indicator" that monitors the advance and retreat of the opal-rich PFZ northward (southward) toward (away from) the Meteor Rise in the subantarctic sector of the South Atlantic Ocean. The timing of PFZ migrations in the subantarctic South Atlantic Ocean is remarkably similar to Pliocene-Pleistocene climate records deduced from benthic oxygen isotope records in the North Atlantic Ocean (
To be complete, carrying out cooperative two-rover science activities would imply making certain ... more To be complete, carrying out cooperative two-rover science activities would imply making certain compromises for each rover. Some important consequences of carrying out cooperative activity include (1) less time available for pursuing each rover's independent objectives, (2) the need to share a landing site that might not be optimized for either rover (e.g., safe site for sky crane and pallet, ExoMars restrictions for a ''go-to'' site, need for hazard avoidance), and (3) the need for some hardware modifications. The cooperative added value of these activities, however, warrants their consideration.
Microbial biosignature assemblages captured within mineral substrates experience extreme pressure... more Microbial biosignature assemblages captured within mineral substrates experience extreme pressures (P) and temperatures (T) during rock burial and metamorphism. We subjected natural microbial biofilms hosted within thermal spring carbonate to six high pressure, high temperature (HPHT) conditions spanning 500 and 800 MPa and 200 to 550 °C, to investigate the initial petrographic transformation of organic and inorganic phases. We find biogenic and amorphous silica mineralises increasingly mature organic matter (OM) as temperature and pressure increase, with OM expelled from recrystallised calcite at the highest HPHT, captured within a quartz phase. Sulfur globules associated with microbial filaments persist across all HPHT conditions in association with microbially-derived kerogen. These data demonstrate how microbial material captured within chemically-precipitated sediments petrographically evolves in high grade rocks during their first stages of transformation.
<p>Two missions are on Mars looking for traces of life (MSL and Mars 2020) while th... more <p>Two missions are on Mars looking for traces of life (MSL and Mars 2020) while the ExoMars mission, slated for launch later this year, is postponed. All missions are equipped with a powerful array of instrumentation for <em>in situ </em>analyses. In addition, the ExoMars rover, Rosalind Franklin, has the advantage of a 2 m drill to penetrate beneath the oxidised and UV-irradiated surface [1]. However, unless phototrophic life forms were able to develop on a planet that was never permanently habitable and that was characterised by punctuated and likely unconnected habitable niches [2, 3], martian life likely remained in a very primitive state of evolution, potentially similar to terrestrial chemotrophs, <em>i.e. </em>discrete, very small cells and colonies that leave even more subtle fossil remains. Indeed, only in the vicinity of nutrient-rich hydrothermal environments can chemotrophic biomass develop to create potentially visible morphological signatures in the form of a clotted texture in the associated sediments – a texture that is not immediately identifiable as a biosignature but that would warrant further analysis of such rocks by other instruments, such as SAM on Curiosity, SHERLOC on Perseverance, or MOMA on Rosalind Franklin.</p> <p>Taking the early terrestrial environment and early life as analogues for habitable environments and primitive life forms on early Mars, it is becoming clearer that the most primitive of life forms known on Earth, chemolithotrophs that obtain energy from oxidation of inorganic substrates (e.g. ferrous iron, hydrogen sulfide, elemental sulfur, thiosulfate, or ammonia), were widely distributed but, because of their very small size (< 1 µm diameter) and very small, heterogeneously distributed colonies (5 µm to some tens of microns), are typically undetectable through bulk analyses (bulk carbon contents are generally 0.01-0.05 %.) (Fig. 1). To compound the challenge, morphologically-recognisable cells are rarely observed, while degraded cells mixed with generic extracellular polymeric substances (EPS) are more frequent. Chemolithotrophs can inhabit sediment particle surfaces and pore space close to the surface or at depth, as long as they have access to nutrients and water. But how to identify them <em>in situ </em>on Mars? Even on Earth with well-equipped, state of the art laboratories, detection and identification of fossil chemolithotrophs is difficult and, often, controversial. The solution requires seeking to simultaneously detect structural information of the organisms’ presence and analyse well-preserved organogeochemical signature with spatial precisions on the order of a micron and detection limits as low as possible. This would be a challenge for Mars Sample Return in the near future.</p> <p><img src="" alt="" /></p> <p><strong>Figure 1. </strong>(A-C) distribution of tiny colonies and EPS clumps (red circles) in a silicified, volcanic sediment [3] at increasing magnifications. Individual dividing cells visible only at maximum resolution in (C).</p> <p><strong>References:</strong> [1] Vago, J.L., et al. (2017) <em>Astrobiology, </em>17: 471–510. [2] Cockell et al., 2012. <em>Icarus, </em>217:184–193. [3] Westall et al., (2015) <em>Astrobiology, </em>17: 998-1029. [4] Author J. et al. (2002) <em>LPS XXXIII</em>, #2110.</p>
The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The... more The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The detection of planets with a wide range of masses demonstrates that extra-solar planets of low mass exist. In this paper we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines including astrophysics, planetary sciences, chemistry and microbiology. Darwin is designed to detect and perform spectroscopic analysis of rocky planets similar to the Earth at mid-infrared wavelengths (6 to 20 µm), where an advantageous contrast ratio between star and planet occurs. The baseline mission lasts 5 years and consists of approximately 200 individual target stars. Among these, 25 to 50 planetary systems can be studied spectroscopically, searching for gases such as CO 2 , H 2 O, CH 4 and O 3. Many of the key technologies required for the construction of Darwin have already been demonstrated and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.
The oldest traces of life on Earth occur in cherts (silicified volcanic silts and sands) that wer... more The oldest traces of life on Earth occur in cherts (silicified volcanic silts and sands) that were deposited in coastal environments ∼3.5 billion years ago [1, 2, 3, 4, 5, 6]. These microfossils are the remains of relatively evolved organisms, implying that life had to have appeared much earlier [6]. However, studies related to the origin of life are hampered by the fact that suitable rocks dating from the first billion years are lacking on Earth, since older materials are too heavily metamorphosed or have been destroyed by plate tectonics. Investigations are now focussed on the search for older microfossils on other planets and, in particular, on Mars. Mars does not appear to have undergone plate tectonic activity as on Earth and, if life appeared on that planet, its fossilised traces could be found embedded in rocks from the
Similarities in the early histories of Mars and Earth suggest that life may have arisen on Mars a... more Similarities in the early histories of Mars and Earth suggest that life may have arisen on Mars as it did on Earth. The early life forms on Mars were probably simple organisms, similar to terrestrial prokaryotes. In fact, given the early deterioration of the Martian climate, it is unlikely that life on Mars could ever have reached more sophisticated evolution. Based on the present knowledge of Mars, the possibility of extant life at the surface is small. However, given the adaptability of terrestrial prokaryotes under adverse conditions, it is not excluded. Any extant life is hypothesized to reside in the permafrost in a dormant state until "reanimated" by impact-caused hydrothermal activity. Using this rationale, a group of European scientists worked together to conceive a hypothetical strategy to search for life on Mars. A possible configuration for a lander/rover is outlined.
Assessing the habitability of Mars and detecting life, if it was ever there, depends on knowledge... more Assessing the habitability of Mars and detecting life, if it was ever there, depends on knowledge of whether the combined environmental stresses experienced on Mars are compatible with life and whether a record of that life could ever be detected. Many combinations of Mars relevant stress factors, such as high radiation dose rates and high UV uences combined with high salt concentrations, and low water activity, have not been investigated. In particular, the response of anaerobic organisms to Mars-like stress factors and combinations thereof are not known. In the EC project MASE (Mars Analogues for Space Exploration) we address these limitations by characterising different Mars analogue environments on Earth, isolating microorganisms from these sites and exposing them to Mars relevant stress factors alone and in combination. We want to find out, if these bacteria respond in an additive or synergistic way and if they would be able to survive on Mars. So far, eight only distantly rela...
In this study, we demonstrate the usefulness of Raman spectroscopy, and in particular Raman mappi... more In this study, we demonstrate the usefulness of Raman spectroscopy, and in particular Raman mapping, as a very powerful tool for the study of both organic matter and minerals associated with silicified biological remains. Our investigations concern silicified organic matter, microorganisms and biological remains of various origins and ages, from the metacherts of Isua, Greenland, 3.8 Ga, to silicified wood from the Petrified Forest National Park, Arizona, USA, 225 Ma.
MOROCCO) INVESTIGATED BY HR-SEM AND TOF-SIMS: FOSSIL ANALOGUES OF MOA-SRB CONSORTIA? B. Cavalazzi... more MOROCCO) INVESTIGATED BY HR-SEM AND TOF-SIMS: FOSSIL ANALOGUES OF MOA-SRB CONSORTIA? B. Cavalazzi, R. Barbieri, G.G. Ori, F. Westall, S.L. Cady, S. Gennaro, A. Lui, R. Canteri, M. Bersani, P. Lazzeri and G. Pepponi, Centre de Biophysique Moléculaire, CNRS, Orléans, FRANCE, Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, ITALY, Int'l Research School of Planetary Sciences, Università d'Annunzio, ITALY, Department of Geology, Portland State University, OR, USA, Fondazione Bruno Kessler, Ricerca Scientifica e Tecnologica, Trento, ITALY.
The MASE (Mars Analogues for Space Exploration) [1] project is a four-year collaborative research... more The MASE (Mars Analogues for Space Exploration) [1] project is a four-year collaborative research project supported by the European Commission Seventh Framework Contract. The aim of the project is to understand how combined environmental stresses influence the habitability of a number of Mars analogue environments in Europe and beyond. Field sites sampled for MASE include deep subsurface salts at Boulby Mine in the UK, sulfidic springs In Germany and an acidic cold lake in lceland. Samples and isolates have also been provided to the project from acidic deep subsurface environments at the Rio Tinto in Spain as well as permafrost sites in Russian Siberia and northern Canada. Crucial to assessing the habitability of any environmental system to be used as an astrobiological analogue • whether for life in general or, as in this case, for anaerobic microorganisms • is a detailed understanding of their geological and physiochemical context [2, 3]. One of the key outcomes of the MASE projec...
The aim of this article is to provide the reader with an overview of the different possible scena... more The aim of this article is to provide the reader with an overview of the different possible scenarios for the emergence of life, to critically assess them and, according to the conclusions we reach, to analyze whether similar processes could have been conducive to independent origins of life on the several icy moons of the Solar System. Instead of directly proposing a concrete and unequivocal cradle of life on Earth, we focus on describing the different requirements that are arguably needed for the transition between non-life to life. We approach this topic from geological, biological, and chemical perspectives with the aim of providing answers in an integrative manner. We reflect upon the most prominent origins hypotheses and assess whether they match the aforementioned abiogenic requirements. Based on the conclusions extracted, we address whether the conditions for abiogenesis are/were met in any of the oceanic icy moons.
Enigmatic microorganisms and life in extreme …, 1999
... Pub 30, 73-90. Poinar, GO.(1992) Life in Amber, Stanford University Press, Stanford. ... Astr... more ... Pub 30, 73-90. Poinar, GO.(1992) Life in Amber, Stanford University Press, Stanford. ... Astract. Westall, F.(1997b) in C. Cosmovici, S. Bowyer and D. Werthimer (eds.) Astronomical and Biochemical Origins and the Search for Life in the Universe, Editori compositrici, Bolgna, pp. ...
... Andreazza g , E-mail The Corresponding Author , Frédéric Foucher a , Jan Toporski h , E-mail ... more ... Andreazza g , E-mail The Corresponding Author , Frédéric Foucher a , Jan Toporski h , E-mail The Corresponding Author , Andrea Jauss h , Volker Thiel i , E-mail The Corresponding Author , Gordon Southam j , E-mail The Corresponding Author , Lachlan MacLean j , Susan ...
A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B ... more A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B together over the interval 0-350 mbsf (0-9 m.y.). High-resolution carbonate and opal data from the cores were correlated with the calcium and silicon signals from the GST logging run in Hole 704B to identify missing and disturbed intervals in the cores. Paleomagnetic and biostratigraphic age boundaries were then transferred to the composite depth records to obtain an age model, and sedimentation rates were calculated by linear interpolation between datums. Algorithms relating measured dry-bulk density to carbonate content and depth were generated to produce predicted values of density for every sample. Accumulation rates of bulk, carbonate, opal, and terrigenous sediment components were then computed to generate a record of sediment deposition on the Meteor Rise that has a resolution of better than 200,000 yr for the period from 8.6 to 1.0 m.y. From 8.6 to 2.5 m.y., bulk-accumulation rates on the Meteor Rise averaged less than 2 g/cm 2 /1000 yr and were dominated by carbonate deposition. The first significant opal deposition (6.0 m.y.) punctuated a brief (less than 0.6 Ma) approach of the Polar Front Zone (PFZ) northward that heralded a period of increasing severity of periodic carbonate dissolution events (terrigenous maxima) that abruptly terminated at 4.8 m.y. (base of the Thvera Subchron), synchronous with the reflooding of the Mediterranean after the Messinian salinity crisis. From 4.8 to 2.5 m.y., carbonate again dominated deposition, and the PFZ was far south except during brief northward excursions bracketing 4.2-3.9, 3.3-2.9, and 2.8-2.7 m.y. At 2.5 m.y., all components of bulk-accumulation rates increased dramatically (up to 15 g/cm 2 /1000 yr), and by 2.4 m.y., a pattern of alternating, high-amplitude carbonate and opal cyclicity marked the initiation of rapid glacial to interglaciál swings in the position of the PFZ, synchronous with the "onset" of major Northern Hemisphere glaciation. Both mass-accumulation rates and the amplitude of the cycles decreased by about 2 m.y., but opal accumulation rates remained high up through the base of the Jaramillo (0.98 m.y.). From 1.9 to 1 m.y., the record is characterized by moderate amplitude fluctuations in carbonate and opal. This record of opal accumulation rates is interpreted as a long-term "Polar Front Indicator" that monitors the advance and retreat of the opal-rich PFZ northward (southward) toward (away from) the Meteor Rise in the subantarctic sector of the South Atlantic Ocean. The timing of PFZ migrations in the subantarctic South Atlantic Ocean is remarkably similar to Pliocene-Pleistocene climate records deduced from benthic oxygen isotope records in the North Atlantic Ocean (
To be complete, carrying out cooperative two-rover science activities would imply making certain ... more To be complete, carrying out cooperative two-rover science activities would imply making certain compromises for each rover. Some important consequences of carrying out cooperative activity include (1) less time available for pursuing each rover's independent objectives, (2) the need to share a landing site that might not be optimized for either rover (e.g., safe site for sky crane and pallet, ExoMars restrictions for a ''go-to'' site, need for hazard avoidance), and (3) the need for some hardware modifications. The cooperative added value of these activities, however, warrants their consideration.
Microbial biosignature assemblages captured within mineral substrates experience extreme pressure... more Microbial biosignature assemblages captured within mineral substrates experience extreme pressures (P) and temperatures (T) during rock burial and metamorphism. We subjected natural microbial biofilms hosted within thermal spring carbonate to six high pressure, high temperature (HPHT) conditions spanning 500 and 800 MPa and 200 to 550 °C, to investigate the initial petrographic transformation of organic and inorganic phases. We find biogenic and amorphous silica mineralises increasingly mature organic matter (OM) as temperature and pressure increase, with OM expelled from recrystallised calcite at the highest HPHT, captured within a quartz phase. Sulfur globules associated with microbial filaments persist across all HPHT conditions in association with microbially-derived kerogen. These data demonstrate how microbial material captured within chemically-precipitated sediments petrographically evolves in high grade rocks during their first stages of transformation.
Uploads
Papers by F. Westall