Book

Life on Earth and other Planetary Bodies (Vol. 24 in "Cellular Origin, Life in Extreme Habitats and Astrobiology")

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Abstract

Summary of Life on Earth and other Planetary Bodies (Introduction of J. Seckbach, § 5) This volume has gathered 68 expert authors from around the world to discuss questions of life on Earth and elsewhere. Their chapters deal with primeval seas, the origin of the genetic code, panspermia, and terrestrial habitability. The Extremophiles section includes the halophiles, the polar cyanobacteria, and life without water, as well as microorganisms tolerating, surviving, and flourishing in severe environments. The extremophiles are important for practical uses (enzyme production) and extraction of special proteins. In the Extraterrestrial Life section of this volume there are discussions about the search for extraterrestrial intelligent life, terrestrial analogues for planetary oceans, life in terrestrial lava-caves, as implications for life detection on other planets, habitability of Earth-like exoplanets, Mars water and polar dunes, Antarctica as a model for life on Europa, Saturn and its moons, astrobiology of Titan, habitability of extrasolar planets and cosmic catastrophes. This volume is number 24 of the Cellular Origin, Life in Extreme Habitats and Astrobiology [COLE] series [J. Seckbach (editor) 1999-2013, www.springer.com/series/5775]. The present book complements previous books of this series discussing also topics associated with this volume, namely, the Science of Astrobiology (2011), Stromatolites (2011), Symbioses and Stress (2010), Algae and Cyanobacteria in Extreme Environments (2007), Enigmatic Microorganisms and Life in Extreme Environments (1999). The target audience for this new book comprises scientists, microbiologists working with extremophiles, biology, geology students, teachers and general readers.
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The interstellar medium has a rich chemistry which involves a wide variety of molecules. Of particular interest are molecules that have a link to prebiotic chemistry which hold the key to understanding of our origins. On the basis of suggestions that selenium may have been involved in the origin and evolution of life, we have studied the selenium analogue of cyanoethenethiol, namely the novel cyanoetheneselenol. Cyanoetheneselenol exhibits conformational and geometrical isomerism. This theoretical work deals with the study of four forms of cyanoetheneselenol in terms of their structural, spectroscopic and thermodynamic parameters. All computations were performed using density functional theory method with the B3LYP functional and the Pople basis set, 6–311 + G(d,p), for all atoms. The relative stability of the four isomers of cyanoetheneselenol was obtained and interpreted. The infrared spectra were generated and assignment of the normal modes of vibration was performed. Probable regions of detection, proposed on the basis of parameters obtained from this study for the four isomers, include comets, the molecular cloud: Sagittarius B2(N), and planetary atmospheres. The molecular and spectroscopic parameters should be useful for future identification of the astrobiological molecule cyanoetheneselenol and the development of the Square Kilometre Array. Graphical Abstract E and Z isomers of cyanoetheneselenol
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The soda ocean hypothesis (Kempe & Degens, 1985) suggests an early alkaline ocean of high pH and low calcium and magnesium convnetrations. The dissolved carbonates were gradually lost during the Precambrian, leaving the present sodium chloride ocean. The Precambrian paleontological record and the calcium physiology of living cells implicate that the stepwise buildup of calcium in the ancient ovean was of primary importance for the generation of multicellular life and the onset of biocalcification.
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Stromatolites are products of benthic microbial communities composed predominantly of photosynthetic microorganisms, mainly cyanobacteria (blue-green algae), with occasional admixture of eukaryotic algae. The microbial communities (mats) may either act as traps for current-transported sediment particles, or they may induce in situ precipitation of minerals, mostly Ca and Mg carbonates. The in situ calcified, laminated microbial mats are classified as stromatolites whereas those characterized by clotted internal structures are termed thrombolites. Both structures can occur together in the same microbial sedimentary deposit and their clear-cut separation is often difficult (for review see: Kennard and James 1986; Burne and Moore 1987). The lamination in stromatolites may reflect diurnal, tidal, synodic, seasonal, annual or irregular growth increments which many produce by accretion in a great variety of macroscopic bodies grouped sometimes into large reefoid structures (e.g. Hofmann 1973; Monty 1973; Walter 1976). Both the trapping and mineralizing algal mats occur today, the former almost exclusively in marine environments, the latter in lagoonal, paralacustrine and lacustrine enviroments. This has not, however, been so in the geologic past: throughout most of the Precambrian stromatolites – the only large and widespread marine biological structures of that time – formed predominantly by in situ mineralization of cyanobacteria-like microbiota (e.g., Monty 1973, Serebryakov and Semikhatov 1974, Awramik 1982). It is still debated why stromatolites are so rare in modern seas and why marine cyanobacterial mats diminished their ability to calcify with the end of the Cretaceous. The present paper attempts to answer Monty’s (1972, p. 747) anxious question concerning the absence of in situ calcification in extant marine cyanobacteria.
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Microbialites are organosedimentary deposits formed from interaction between benthic microbial communities (BMCs) and detrital or chemical sediments. Processes involved in the formation of calcareous microbialites include trapping and binding of detrital sediment (forming microbial boundstones), inorganic calcification (forming microbial tufa), and biologically influenced calcification (forming microbial framestones). Microbialites contrast with other biological sediments in that they are generally not composed of skeletal remains. -from Authors
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Summary The results of detailed hydrochemical and biosedimentological studies of the sea-linked Satonda Crater Lake, Sumbawa Island/Indonesia are presented. They revealed that the mildly alkaline, mid-water stratified and species-poor lake supports growth of cyanobacterial-red algal calcareous reefs comparable with some ancient marine biocarbonates. The chemical and biotic changes during the last 4,000 years of the lake history have been reconstructed. They indicate that the chemistry of the lake evolved from initially fresh water, through highly alkaline to the modern slightly alkaline quasi-marine conditions with corresponding biotic changes. The influence of the 1815 eruption of the nearby located Tambora Volcano on the lake chemistry and resulting lithological and biotic changes is also discussed. The lake proves to be a good model for the recently proposed hypothesis of an early alkaline (soda) ocean.
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MICROBIALITES are organosedimentary deposits produced by benthic microbial communities interacting with detrital or chemical sediments1. Calcareous cyanobacterial microbialites defined as stromatolites and thrombolites were common in ancient shallow marine environments2. Today, they are restricted to a few lacustrine and perimarine settings. This restriction may result from changes in seawater chemistry through time3–6, particularly from alteration in supersaturation with respect to carbonate minerals7. The largest known calcareous microbialites (several metres high) were formed in the late Precambrian8. Here we report the discovery of enormous (~40 m high) tower-like microbialites from alkaline (pH>9.7) Lake Van, eastern Anatolia. Growth is by mats of coccoid cyanobacteria (Pleurocapsa group) permineralizing in situ with aragonite and by inorganically precipitated calcite. Certain aspects of these microbialites resemble Proterozoic marine stromatolites9.
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Major ion compositions of primary fluid inclusions from terminal Proterozoic (ca. 544 Ma) and Early Cambrian (ca. 515 Ma) marine halites indicate that seawater Ca{sup 2+} concentrations increased approximately threefold during the Early Cambrian. The timing of this shift in seawater chemistry broadly coincides with the 'Cambrian explosion,' a brief drop in marine {sup 87}Sr/{sup 86}Sr values, and an increase in tectonic activity, suggesting a link between the advent of biocalcification, hydrothermal mid-ocean-ridge brine production, and the composition of seawater. The Early Cambrian surge in oceanic [Ca{sup 2+}] was likely the first such increase following the rise of metazoans and may have spurred evolutionary changes in marine biota.
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Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo'ou Island (Vai Lahi and Vai Si'i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo'ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite, calcite, siderite), which, due to recrystallization, had already annihilated the cellular morphology of the mineralized microbiota or (b) relatively late primary silicification of already highly degraded and no longer morphologically identifiable microbial remains.
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A concept explaining biocalcification as a form of calcium detoxification is advanced using geochemical and paleontological criteria. The first appearence of calcareous skeletons at the turn of the Precambrian/Cambrian is interpreted as a biotic response to a gradual rise of Ca2+ in world ocean resulting in Ca2+ stress environments in shelf areas. Periodic appearance in the Phanerozoic record of heavily calcified marine biota, absent or relic in modern seas, suggests considerable temporal fluctuations of calcium concentrations in the ancient ocean. Temporal changes in Ca2+ and mineral nutrient contents in the environment can thus be seen as overriding factors in the evolution of organisms.
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The structure, mineralogy, and accretion processes of the modern and subfossil cyanobacterial microbialites from the alkaline crater lake Alchichica (Puebla, Mexico) were studied, along the lake's bathymetry and hydrochemistry. The recent lowering of the lake level had exposed microbialitic carbonate mounds and crusts, which emerged up to 2 m above the water surface, while accreting cyanobacterial microbialites were present down to a depth of ~15 m. Morphological and molecular analysis found that the living cyanobacterial mats were composed of diverse filamentous and coccoid cyanobacteria (Nostocales, Chroococcales, Oscillatoriales, and Pleurocapsales). The emerged subfossil microbialites comprised two generations: "white" (domes and crusts composed mainly of hydromagnesite with an admixture of huntite and calcite, 238U/230Th age of ~2.8 ka BP), and "brown" (chimneys, columns and laminated crusts composed of aragonite with an admixture of Mg-calcite, 238U/230Th age of ~1.1 ka BP). The significant age, structural, mineralogical, and isotopic differences suggest that the two generations were formed in different environmental conditions: the "white" during a dry period, and the "brown" in wet climate associated with high water level and intense inflow of ground water, which lowered the Mg/Ca ratio resulting in formation of aragonite instead of hydromagnesite. The hydromagnesite, replacing the primary aragonite precipitated in the living cyanobacterial biofilm, frequently undergoes silicification, which obliterates both the primary structure of the carbonate and the enclosed remains of cyanobacterial microbiota. This process helps to explain the abundant formation of dolomites and cherts in an allegedly highly alkaline Early Precambrian ocean. Thus, Lake Alchichica represents a modern alkaline environment where biosedimentary structures resembling Precambrian deposits are generated.
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A suite of young volcanic basaltic lavas erupted on the intra-plate island of Niuafo’ou and at active rifts and spreading centres (the King’s Triple Junction and the Northeastern Lau Spreading Centre) in the northern Lau Basin is used to examine the pattern of mantle flow and the dynamics of melting beneath this complex back-arc system. All lavas contain variable amounts of a subduction related component inherited from the Tonga subduction zone to the east. All lavas have higher 87Sr/86Sr, lower 143Nd/144Nd and more radiogenic Pb isotope compositions than basalts erupted at the Central Lau Spreading Centre in the central Lau Basin, and are interpreted as variable mixtures of subduction-modified, depleted upper mantle, and mantle residues derived from melting beneath the Samoan Islands which has leaked through a tear in the subducting Pacific Plate beneath the Vitiaz Lineament at the northern edge of the Lau Basin. Our data can be used to map out the present-day distribution of Samoan mantle in this region, and show that it influences the compositions of lavas erupted as far as 400km from the Samoan Islands. The distribution of Samoan-influenced lavas implies south- and southwest-wards mantle flow rates of >4cm/year. U-series disequilibria in historic Niuafo’ou lavas have average (230Th/238U)=1.13, (231Pa/235U)=2.17, (226Ra/230Th)=2.11, and together with major and trace element data require ∼5% partial melting of mantle at between 2 and 3GPa, with a residual porosity of 0.002 and an upwelling rate of 1cm year−1. We suggest that intraplate magmatism in the northern Lau Basin results from decompression melting during southward flow of mantle from beneath old (110–120Ma), relatively thick Pacific oceanic lithosphere to beneath young (<5Ma), thinner oceanic lithosphere beneath the northern Lau Basin.
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Saline, 450-m-deep Lake Van (Eastern Anatolia, Turkey) is, with 576km3, the third largest closed lake on Earth and its largest soda lake. In 1989 and 1990, we investigated the hydrochemistry of the lake’s water column and of the tributary rivers. We also cored the Postglacial sediment column at various water depths. The sediment is varved throughout, allowing precise dating back to ca. 15ka BP. Furthermore, lake terrace sediments provided a 606-year-long floating chronology of the Glacial high-stand of the lake dating to 21cal. ka BP. The sediments were investigated for their general mineralogical composition, important geochemical parameters, and pore water chemistry as well. These data allow reconstructing the history of the lake level that has seen several regressions and transgressions since the high-stand at the end of the Last Glacial Maximum. Today, the lake is very alkaline, highly supersaturated with Ca-carbonate and has a salt content of about 22gkg−1. In summer, the warmer epilimnion is diluted with river water and forms a stable surface layer. Depth of winter mixing differs from year to year but during time of investigation the lake was oxygenated down to its bottom. In general, the lake is characterized by an Na–CO3–Cl–(SO4)-chemistry that evolved from the continuous loss of calcium as carbonate and magnesium in the form of Mg-silica-rich mineral phases. The Mg cycle is closely related to that of silica which in turn is governed by the production and dissolution of diatoms as the dominant phytoplankton species in Lake Van. In addition to Ca and Mg, a mass balance approach based on the recent lake chemistry and river influx suggests a fractional loss of potassium, sodium, sulfur, and carbon in comparison to chloride in the compositional history of Lake Van. Within the last 3ka, minor lake level changes seem to control the frequency of deep water renewal, the depth of stratification, and the redox state of the hypolimnion. Former major regressions are marked by Mg-carbonate occurrences in the otherwise Ca-carbonate dominated sediment record. Pore water data suggest that, subsequent to the major regression culminating at 10.7ka BP, a brine layer formed in the deep basin that existed for about 7ka. Final overturn of the lake, triggered by the last major regression starting at about 3.5ka BP, may partly account for the relative depletion in sulfur and carbon due to rapid loss of accumulated gases. An even stronger desiccation phase is proposed for the time span between about 20 and 15ka BP following the LGM, during which major salts could have been lost by precipitation of Na-carbonates and Na-sulfates.
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The viewpoint in this paper is that the distinction of detrital from in-situ precipitated carbonate in stromatolites is vital so that the appropriate modern analogues can be sought. Reviewing literature on modern stromatolites, it is clear that marine stromatolites are dominated by detrital sediment, although diagenetic processes can obscure the detrital nature of carbonate. In mats in low salinity conditions carbonate is dominantly of precipitate origin, being triggered by photosynthesis. In mats in saline conditions petrographically-similar precipitates occur, apparently triggered variously by photosynthesis, evaporation and organic matter degradation in different cases. Light carbon isotopes in the carbonate are a good pointer to organic degradation as a carbon source.A review of criteria proposed for identifying the origin of carbonate in Precambrian stromatolites shows that in different cases reliable evidence both for sediment incorporation and carbonate precipitation has been obtained, although many arguments are equivocal. The utility of luminescence petrography for positive identification of detritus, and carbon isotope data for identification of carbon sources is outlined.New petrographic and carbon isotope data are presented from four units: Canyon Formation of East Greenland; Draken and Wilsonbreen Formations of Spitsbergen and Atar Group, Mauritania. Although environmentally diverse, each displays evidence for both sediment incorporation and localized carbonate precipitation, although in widely varying proportions. It is recommended that luminescence studies be carried out for stromatolite microstructural work. Carbon isotope data indicate no distinction between early (“inorganic”) cements, stromatolitic and non-stromatolitic (dolo)micrites, and indicate a common origin related to water column and microbial mat photosynthesis, variably accompanied by evaporation.
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It is unknown when life first appeared on Earth. The earliest known microfossils (approximately 3,500 Myr before present) are structurally complex, and if it is assumed that the associated organisms required a long time to develop this degree of complexity, then the existence of life much earlier than this can be argued. But the known examples of crustal rocks older than 3,500 Myr have experienced intense metamorphism, which would have obliterated any fragile microfossils contained therein. It is therefore necessary to search for geochemical evidence of past biotic activity that has been preserved within minerals that are resistant to metamorphism. Here we report ion-microprobe measurements of the carbon-isotope composition of carbonaceous inclusions within grains of apatite (basic calcium phosphate) from the oldest known sediment sequences--a approximately 3,800-Myr-old banded iron formation from the Isua supracrustal belt, West Greenland, and a similar formation from the nearby Akilia island that is possibly older than 3,850 Myr. The carbon in the carbonaceous inclusions is isotopically light, indicative of biological activity; no known abiotic process can explain the data. Unless some unknown abiotic process exists which is able both to create such isotopically light carbon and then selectively incorporate it into apatite grains, our results provide evidence for the emergence of life on Earth by at least 3,800 Myr before present.
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Calcium is among the most commonly used ions, in a multitude of biological functions, so much so that it is impossible to imagine life without calcium. In this article I have attempted to address the question as to how calcium has achieved this status with a brief mention of the history of calcium research in biology. It appears that during the origin and early evolution of life the Ca2+ ion was given a unique opportunity to be used in several biological processes because of its unusual physical and chemical properties.
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Recent discoveries about Europa--the probable existence of a sizeable ocean below its ice crust; the detection of hydrated sodium carbonates, among other salts; and the calculation of a net loss of sodium from the subsurface--suggest the existence of an alkaline ocean. Alkaline oceans (nicknamed "soda oceans" in analogy to terrestrial soda lakes) have been hypothesized also for early Earth and Mars on the basis of mass balance considerations involving total amounts of acids available for weathering and the composition of the early crust. Such an environment could be favorable to biogenesis since it may have provided for very low Ca2+ concentrations mandatory for the biochemical function of proteins. A rapid loss of CO2 from Europa's atmosphere may have led to freezing oceans. Alkaline brine bubbles embedded in ice in freezing and impact-thawing oceans could have provided a suitable environment for protocell formation and the large number of trials needed for biogenesis. Understanding these processes could be central to assessing the probability of life on Europa.
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All life is organized as cells. Physical compartmentation from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, hence inorganic matter with such attributes would be life's most likely forebear. We propose that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyse the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments, which furthermore restrained reacted products from diffusion into the ocean, providing sufficient concentrations of reactants to forge the transition from geochemistry to biochemistry. The chemistry of what is known as the RNA-world could have taken place within these naturally forming, catalyticwalled compartments to give rise to replicating systems. Sufficient concentrations of precursors to support replication would have been synthesized in situ geochemically and biogeochemically, with FeS (and NiS) centres playing the central catalytic role. The universal ancestor we infer was not a free-living cell, but rather was confined to the naturally chemiosmotic, FeS compartments within which the synthesis of its constituents occurred. The first free-living cells are suggested to have been eubacterial and archaebacterial chemoautotrophs that emerged more than 3.8 Gyr ago from their inorganic confines. We propose that the emergence of these prokaryotic lineages from inorganic confines occurred independently, facilitated by the independent origins of membrane-lipid biosynthesis: isoprenoid ether membranes in the archaebacterial and fatty acid ester membranes in the eubacterial lineage. The eukaryotes, all of which are ancestrally heterotrophs and possess eubacterial lipids, are suggested to have arisen ca. 2 Gyr ago through symbiosis involving an autotrophic archaebacterial host and a heterotrophic eubacterial symbiont, the common ancestor of mitochondria and hydrogenosomes. The attributes shared by all prokaryotes are viewed as inheritances from their confined universal ancestor. The attributes that distinguish eubacteria and archaebacteria, yet are uniform within the groups, are viewed as relics of their phase of differentiation after divergence from the non-free-living universal ancestor and before the origin of the free-living chemoautotrophic lifestyle. The attributes shared by eukaryotes with eubacteria and archaebacteria, respectively, are viewed as inheritances via symbiosis. The attributes unique to eukaryotes are viewed as inventions specific to their lineage. The origin of the eukaryotic endomembrane system and nuclear membrane are suggested to be the fortuitous result of the expression of genes for eubacterial membrane lipid synthesis by an archaebacterial genetic apparatus in a compartment that was not fully prepared to accommodate such compounds, resulting in vesicles of eubacterial lipids that accumulated in the cytosol around their site of synthesis. Under these premises, the most ancient divide in the living world is that between eubacteria and archaebacteria, yet the steepest evolutionary grade is that between prokaryotes and eukaryotes.
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Calcareous or dolomitic, often secondarily silicified, laminated microbial structures known as stromatolites are important keys to reconstruct the chemical and biotic evolution of the early ocean. Most authors assume that cyanobacteria-associated microbialitic structures described from Shark Bay, Western Australia, and Exuma Sound, Bahamas, represent modern marine analogues for Precambrian stromatolites. Although they resemble the Precambrian forms macroscopically, their microstructure and mineralogical composition differ from those characterizing their purported ancient counterparts. Most Precambrian stromatolites are composed of presumably in situ precipitated carbonates, while their assumed modern marine analogues are predominantly products of accretion of grains trapped and bound by microbial, predominantly cyanobacterial, benthic mats and biofilms and only occasionally by their physicochemical activity. It has therefore been suggested that the carbonate chemistry of early Precambrian seawater differed significantly from modern seawater, and that some present-day quasi-marine or non-marine environments supporting growth of calcareous microbialites reflect the hydrochemical conditions controlling the calcification potential of Precambrian microbes better than modern seawater. Here we report the discovery of a non-marine environment sustaining growth of calcareous cyanobacterial microbialites showing macroscopic and microscopic features resembling closely those described from many Precambrian stromatolites.
Book
The purpose of the present volume is to give a comprehensive and up-to-date 2 survey of the nature and role of calcium ions (Ca +) in the regulation of cel­ 2 lular function. Since Ca + has gained in interest over the past years as a cel­ lular messenger in signal transduction, and since the discovery of its cellular receptor protein, calmodulin, has helped in understanding its mode of action in molecular terms, we felt that an interdisciplinary selection of topics from the calcium field could provide a good source of information for all those in­ terested in calcium-mediated physiology. The volume begins with an overview on the synarchic nature of the two 2 cellular messengers, cyclic AMP and Ca +. The next three chapters deal with 2 the various transport mechanisms for Ca +. The biochemistry and molecular biology of calmodulin, as well as the cellular localization of calmodulin and calmodulin-binding proteins, are reviewed. Calcium regulation of smooth muscle contraction introduces the pharmacology of calcium antagonists.
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This chapter presents an attempt to classify late Precambrian stromatolite microstructures. The stromatolite primary lamination reflects the growth pattern of the algal coenose and the habit of the carbonate precipitated or trapped within the filament framework, among other things. The fossil stromatolite microstructure includes furthermore the imprint of subsequent diagenesis. A carefully detailed description of the actual fabric of the microstructure mixing up original and diagenetic features leads to an excessive number of microstructural patterns, and a very artificial classification. The need of modern models is great because of the excessive attention paid by the geologists to the sedimentary and physical processes. Well-preserved microstructures were proposed for the classification of stromatolites that were well adapted: (1) simple microstructures where the laminations or the dominant fabrics follow the rhythmical growth pattern of the coenose; and (2) complex microstructures where the historical succession of laminations presents microstructural changes due to seasonal differentiation of the algal coenose.
Article
Thrombolites and stromatolites are distinct types of microbial (cryptalgal) structures characterized, respectively, by mesoscopic clotted and laminated internal fabrics. Thrombolites are not uniformly distributed in the rock record, but are essentially a Cambrian and Lower Ordovician phenomenon. Their distribution appears to have been controlled by, first, the appearance of calcareous microbes (including such forms as Girvanella, Renalcis, Epiphyton, and Nuia) and the approximately synchronous radiation and skeletonization of grazing and bioturbating Metazoa at the beginning of the Phanerozoic eon; and second, niche competition from newly evolved, reef-building, skeletal metazoans and algae, and possibly increased predation by molluscs, in Early and Middle Ordovician time.-from Authors
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The sheet cracks, which formed from expansion of the microbial mat and associated sediment, stayed in communication with sea-water until they became filled with marine cement. Some microfossils show laminae and a fibrous microstructure whereas others consist of cement-filled chambers or hematitic clots devoid of obvious microstructure. -from Authors
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The basic properties of living systems are remarkably consistent and involve energy interactions between intracellular and extracellular environments. These interactions predispose living systems to deposit minerals from many solutions. The evolution of biomineralisation was not a single cellular invention but rather the association and perfection of a few of these fundamental properties of cell biology. The components of biomineralisation systems involve some mechanism for modifying the activity of at least one ion, an interface for initiating and possibly controlling crystal growth, a diffusion limited size and a mechanism for manipulating the growth of the crystal lattice. The evolution of these components of biomineralisation in the context of geological time inevitably concentrates on the Precambrian–Cambrian boundary. Over a time scale of less than 50 × 106 years there was a proliferation of metazoan phyla, the mineralisation in a large number of taxa and the exploitation of a diverse set of processes involving agglutinated sediments, silica, phosphates and carbonates. A large number of theories have been proposed to explain why biomineralisation occurred at this particular time. Such theories should recognise the importance of the incorporation of the citric acid cycle into the cellular metabolism of many organisms and its exploitation in an aerobic environment, the development of multicellularity which enormously increased the opportunities for modifying ion activities in diffusion-limited sites, and the exploitation of browsing and carnivorous feeding habits. These influences had major effects on ecosystems and population structures and put considerable selective pressure on the advantages that could be gained from a skeleton.
Article
Major element, trace element, and mineral analyses of rocks from the island of Niuafo'ou in the western Pacific Ocean show that Niuafo'ou rocks have a marked similarity to ocean-floor basalt, especially with basalt of relatively high FeO*/MgO ratios.
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The mode of formation and environmental setting of stromatolites from the lower Missoula Group (ca. 1.1·10⁹ years old) in Glacier National Park, Montana, have been determined. The stromatolite-bearing interval in the lower Missoula Group was deposited in a shallow, intermittently exposed setting of very low relief, the stromatolites forming during periods of submergence. In situ carbonate precipitation was the dominant process involved in the formation of encrusting stromatolitic laminae. This precipitate was deposited within, and probably beneath, algal mats, most likely as a result of the photosynthetic removal of carbon dioxide by the mat-building microscopic algae. Calcite also was precipitated in several types of open-space structures occurring within these stromatolites. Other laminae were produced by the organic stabilization of detrital particles; by the solely physical accumulation of terrigenous material; and probably, by bacterially induced precipitation of iron sulfide which was later oxidized to form hematite layers.
Article
In analogy to modern soda lakes commonly associated with volcanic regions, it is postulated that the ancient sea had a high alkalinity, a high pH and low Ca and Mg concentrations. The change towards NaCl dominance as observed in the present-day ocean can best be explained by a series of mineral equilibria, crustal differentiation and life processes. In principle hydrothermal leaching of chlorine from the oceanic crust caused this ion to accumulate in the sea while at the same time dissolved carbonates became gradually removed by organisms and carbonates. The switch from a soda to a halite ocean was accomplished ca. 1 Ga ago. Crititcal biochemical events marking the chemical evolution of the Precambrian sea and their implications for the PCO2 in air will be discussed.
Article
One hundred and twenty-four carbonate samples from the meta-sedimentary sequence of the 3.7 × 109 yr old Isua supracrustal belt (W-Greenland) have yielded a δ13Ccarb average of −2.5 ± 1.7%. vs PDB and a δ18Ocarb average of +13.0 ± 2.5%. vs SMOW. The oxygen mean comes fairly close to the averages of other early Precambrian carbonates. The carbon average, however, is some 2%. more negative than those of younger marine carbonates. In terms of a simple terrestrial 13C mass balance, if δ13Ccarb values are original sedimentary values, this more negative δ13C average would imply a considerably smaller ratio in the sedimentary shell during Isua times, and would thus support the concept of a gradual buildup of a sedimentary reservoir of organic carbon during the early history of the Earth. Since, however, the Isua supracrustal rocks have experienced amphibolite-grade metamorphism, which in other areas has been shown to lower δ13Ccarb values, it is most likely that the original values of these rocks were approx 0%.. This indicates that Corx and Ccarb were present in the ancient carbon reservoir in about ‘modern’ proportions. Unless this early stabilization of the terrestrial carbon cycle in terms of a constant partitioning of carbon between the reduced and oxidized species is shown to have been caused by some inorganic geochemical process, a considerably earlier start of chemical evolution and spontaneous generation of life must be considered than is presently accepted.
Article
The microfossil Frutexites is known from many Palaeozoic and some Proterozoic carbonate sedimentary rocks. We recently found unusually well-preserved examples in the early Proterozoic Gunflint Iron Formation of Ontario, Canada. These are preserved in chert, along with other microfossils of the Gunflint microbiota. The Gunflint examples have previously been described as laminated, columnar-branching microstromatolites. We have found narrow tubes (interpreted as trichome moulds) axially placed in many of the microcolumns. By comparison with extant organisms, we interpret Frutexites as a thick-sheathed scytonematacean cyanophyte. These are the oldest known fossil scytonemataceans. They apparently grew within mats of other microorganisms. These probably were photosynthetic organisms, which may have significant implications in the interpretation of some occurrences, such as in the fore-reef facies of Devonian reefs in Western Australia.
Article
GLORIA imagery of the Lau Basin north of 17S shows several morphotectonic terrains: a basement ridge and sedimented inter-ridge area in the SE; a nascent triple junction in the NE; a deeply sedimented basinal terrain in the central area; a linear neovolcanic zone striking NNESSW in the NW; and the northern flank of a leaky transform, the Peggy Ridge. Extension is now being accommodated at two main areas of spreading, but as no site of persistent long-term backarc crustal accretion is evident in this 250-km-wide portion of the basin, we conclude that past extension was largely by formation of pull-apart basins and local magmatism.
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Theoretical geochemical considerations (Kempe and Degens, 1985) and field work at sites of active growth of in situ calcified cyanobacterial mats and biofilms (e.g., Kempe et al., 1991; Kempe and Kazmierczak, 1993; Kazmierczak and Kempe, 2006) convinced us that in the past the ocean must have been more alkaline than at present and that it was of higher CaCO3 supersaturation (SICalcite > 0.8) (Kempe and Kazmierczak, 1990a, 1994; Kazmierczak et al., 2004). Two processes contributed to the higher alkalinity: (1) the slowly declining high primary alkalinity established in the Hadean ocean by binding large amounts of degassed and cometary CO2 through silicate weathering as CO2- 3 and HCO- 3 in ocean waters (“Soda Ocean”) and (2) the effect of the export of excess alkalinity from sulfate reduction processes in stagnant marine basins (“Alkalinity Pump”) (Kempe, 1990; Kempe and Kazmierczak, 1994). The latter alkalinity source started to be effective only after enough sulfate became available in the ocean (probably during the last 1.0–0.8 Ga – for evaluation of sulfate level in the Precambrian ocean see e.g., Buick, 1992; Grotzinger and Kasting, 1993; Eriksson et al., 2005). It could be the single most important factor for short-term modifications of Phanerozoic ocean chemistry. Sudden, in geological terms, export of alkalinity from overturning anaerobic basins could cause high pH and Ca2+ stress upon the marine biota (Kempe and Kazmierczak, 1994; Brennan et al. 2004; Kazmierczak and Kempe, 2004b), and is associated with negative δ13C excursions in carbonate sequences at the Precambrian/Cambrian transition (e.g., Knoll et al., 1986; Magaritz, 1989; Magaritz et al., 1991), where biocalcification started in several phyla almost simultaneously (e.g., Lowenstam and Margulis, 1980; Lowenstam and Weiner, 1989).
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This paper develops the concept that the dramatic appearance of calcareous skeletons in the Lower Cambrian is directly related to the origin of refined mechanisms of intracellular modulation of calcium ion concentration. An homologous family of calcium modulated proteins has recently been discovered. These proteins contain "EF hands", involved in the maintenance of low concentrations of intracellular calcium and the informational use of calcium ion flow (Kretsinger, 1977). The evolution of this specialized calcium physiology, especially in muscle systems, coupled with natural selection by predators are identified as some of the preadaptations for the impressive Tommotian diversification of calcified metazoans. The distribution of calcium biominerals in the phyla of the five kingdoms and the time of first appearance of calcareous mineralization in the fossil record are tabulated. Macroscopic calcified hard parts apparently required the prior evolution of certain cell, tissue and organ system physiologies which are briefly discussed here.