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Billion Years (billion + year)
Selected AbstractsThe Mermaid's Tale: Four Billion Years of Cooperation in the Making of Living Things by Kenneth Weiss and Anne BuchananAMERICAN ANTHROPOLOGIST, Issue 1 2010John H. Relethford No abstract is available for this article. [source] Book review: The Mermaid's Tale: Four Billion Years of Cooperation in the Making of Living ThingsAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2010Michael E. Hochberg No abstract is available for this article. [source] Star cluster ecology , V. Dissection of an open star cluster: spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Simon F. Portegies Zwart ABSTRACT We have modelled in detail the evolution of rich open star clusters such as NGC 2516, NGC 2287, Pleiades, Praesepe, Hyades, NGC 2660 and 3680, using simulations that include stellar dynamics as well as the effects of stellar evolution. The dynamics is modelled via direct N -body integration, while the evolution of single stars and binaries is followed through the use of fitting formulae and recipes. The feedback of stellar and binary evolution on the dynamical evolution of the stellar system is taken into account self-consistently. Our model clusters dissolve in the tidal field of the Galaxy in a time-span of the order of a billion years. The rate of mass loss is rather constant, ,1 M, per million years. The binary fraction at first is nearly constant in time, then increases slowly near the end of a cluster's lifetime. For clusters which are more than about 108 yr old the fractions of stars in the form of binaries, giants and merger products in the inner few core radii are considerably higher than in the outer regions, beyond the cluster's half-mass radius. When stars with masses ,2 M, escape from the cluster, they tend to do so with velocities higher than average. The stellar merger rate in our models is roughly one per 30 million years. Most mergers are the result of unstable mass transfer in close binaries (,70 per cent), but a significant minority are caused by direct encounters between single and binary stars. While most mergers occur within the cluster core, even beyond the half-mass radius stellar mergers occasionally take place. We notice a significant birth rate of X-ray binaries, most containing a white dwarf as the mass acceptor. We also find one high-mass X-ray binary with a neutron-star accretor. If formed and retained, black holes participate in many (higher-order) encounters in the cluster centre, resulting in a large variety of exotic binaries. The persistent triple and higher-order systems formed in our models by dynamical encounters between binaries and single stars are not representative for the multiple systems observed in the Galactic disc. We conclude that the majority of multiples in the disc probably formed when the stars were born, rather than through later dynamical interactions. [source] Front and Back Covers, Volume 22, Number 2.ANTHROPOLOGY TODAY, Issue 2 2006April 200 Front and back cover caption, volume 22 issue 2 Front & back cover ANTHROPOLOGY AND THE SEARCH FOR EXTRATERRESTRIAL LIFE. The debate around the likelihood of humans encountering extraterrestrial life is based in the broad context of cosmic evolution, which encompasses astronomical, biological and socio-cultural evolution. In this depiction of cosmic evolution from the US National Aeronautics Space Administration (NASA), the upper left portion shows the formation of stars, the production of heavy elements and the formation of planetary systems, including our own. On the lower left-hand side prebiotic molecules, RNA and DNA are formed within the first billion years on the primitive Earth. The centre shows the origin and evolution of life leading to increasing complexity, culminating with intelligence, culture, and the astronomers who contemplate the universe on the upper right. The image was created by David DesMarais, Thomas Scattergood and Linda Jahnke at NASA's Ames Research Center in 1986, and reissued in 1997. In this issue Steven J. Dick, Chief Historian at NASA, recounts the history of anthropological involvement in the search for extraterrestrial intelligence, and discusses SETI's broader relevance to anthropology. Anthropologists are uniquely qualified by knowledge and training to contribute to SETI, since central concerns when and if contact is made will include socio-cultural difference and cross-cultural communication. In turn the extraterrestrial perspective has much to offer anthropology, both in expanding its boundaries, its insights and its tools, and in casting a fresh light on cultures on Earth. Valerie Olson, in her review of the session dedicated to SETI at the 2005 American Anthropological Association Annual Meeting, argues that the SETI vision of a terrestrial/extraterrestrial dichotomy between human and alien ,others' brings older and more recent anthropological ideas into a new juxtaposition, and that SETI has potential for stimulating the anthropological imagination. [source] Nearby stars of the Galactic disk and halo.ASTRONOMISCHE NACHRICHTEN, Issue 1 2004Abstract High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk , our "familiar Milky Way" , came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy , and by inference many other spirals as well , if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at , , 200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the highresolution spectroscopic tracings, whereas the visual binary , Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a complete account of the UrsaMajor Association is presented, and we provide as well plain evidence for another, the "Hercules-Lyra Association", the likely existence of which was only realized in recent years. On account of its rotation, chemistry, and age we do confirm that the Sun is very typical among its G-type neighbors; as to its kinematics, it appears however not unlikely that the Sun's known low peculiar space velocity could indeed be the cause for the weak paleontological record of mass extinctions and major impact events on our parent planet during the most recent Galactic plane passage of the solar system. Although the significance of this correlation certainly remains a matter of debate for years to come, we point in this context to the principal importance of the thick disk for a complete census with respect to the local surface and volume densities. Other important effects that can be ascribed to this dark stellar population comprise (i) the observed plateau in the shape of the luminosity function of the local FGK stars, (ii) a small though systematic effect on the basic solar motion, (iii) a reassessment of the term "asymmetrical drift velocity" for the remainder (i.e. the thin disk) of the stellar objects, (iv) its ability to account for the bulk of the recently discovered high-velocity blue white dwarfs, (v) its major contribution to the Sun's ,220 km s,1 rotational velocity around the Galactic center, and (vi) the significant flattening that it imposes on the Milky Way's rotation curve. Finally we note a high multiplicity fraction in the small but volume-complete local sample of stars of this ancient population. This in turn is highly suggestive for a star formation scenario wherein the few existing single stellar objects might only arise from either late mergers or the dynamical ejection of former triple or higher level star systems. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fifty thousand galaxies at a glanceASTRONOMY & GEOPHYSICS, Issue 3 2002Klaus Meisenheimer Klaus Meisenheimer and Christian Wolf look forward to COMBO-17, a deep sky survey that should make it possible to bridge the gap between matter in the early universe and the pattern of galaxies that we see today. Abstract The COMBO-17 survey should significantly improve our understanding of galaxy evolution during the last 10 billion years in detail, given its multicolour method to determine redshifts and spectral types for 40 000 galaxies within more than a square degree of sky. In addition, mass determination in the supercluster A901/902 should give significant information about the total mass and distribution of dark matter in the universe. In particular, it should be possible to derive new results about the relative distribution of luminous and dark matter. We see this as a significant step in order to answer a decisive question of cosmology: how did the galaxies form from the density peaks in the early universe? [source] Basin evolution, diagenesis and uranium mineralization in the Paleoproterozic Thelon Basin, Nunavut, CanadaBASIN RESEARCH, Issue 3 2010Eric E. Hiatt ABSTRACT The Paleoproterozoic (Statherian) Thelon Basin is located in the Churchill Province of the Canadian Shield, formed following the Trans-Hudson Orogeny. Basin formation followed an interval of felsic volcanism and weathering of underlying bedrock. The diagenetic evolution of the Thelon lasted about one billion years and was punctuated by fluid movement influenced by tectonic events. Early quartz cements formed in well-sorted, quartz-rich facies during diagenetic stage 1; fluids in which these overgrowths formed had ,18O values near 0, (Vienna Standard Mean Ocean Water). Uranium-rich apatite cement (P1) also formed during diagenetic stage 1 indicating that oxygenated, uranium-bearing pore water was present in the basin early in its diagenetic history. Syntaxial quartz cement (Q1) formed in water with ,18O from ,4 to ,0.8, in diagenetic stage 2. Diagenetic stage 3 occurred when the Thelon Formation was at ca. 5 km depth, and was marked by extensive illitization, alteration of detrital grains, and uranium mineralization. Basin-wide, illite crystallized at ,200 °C by fluids with ,18O values of 5,9, and ,D values of ,60 to ,31,, consistent with evolved basinal brines. Tectonism caused by the accretion of Nena at ca. 1600 Ma may have provided the mechanism for brine movement during deep burial. Diagenetic stage 4 is associated with fracturing and emplacement of mafic dikes at ca. 1300 Ma, quartz cement (Q3) in fractures and vugs, further illitization, and recrystallization of uraninite (U2). Q3 cements have fluid inclusions that suggest variable salinities, ,18O values of 1.5,9,, and ,D values of ,97 to ,83, for stage 4 brines. K-feldspar and Mg-chlorite formed during diagenetic stage 5 at ca. 1000 Ma in upper stratigraphic sequences, and in the west. These phases precipitated from low-temperature, isotopically distinct fluids. Their distribution indicates that the basin hydrostratigraphy remained partitioned for >600 Ma. [source] Life, information, entropy, and time: Vehicles for semantic inheritanceCOMPLEXITY, Issue 1 2007Antony R. Crofts Abstract Attempts to understand how information content can be included in an accounting of the energy flux of the biosphere have led to the conclusion that, in information transmission, one component, the semantic content, or "the meaning of the message," adds no thermodynamic burden over and above costs arising from coding, transmission and translation. In biology, semantic content has two major roles. For all life forms, the message of the genotype encoded in DNA specifies the phenotype, and hence the organism that is tested against the real world through the mechanisms of Darwinian evolution. For human beings, communication through language and similar abstractions provides an additional supra-phenotypic vehicle for semantic inheritance, which supports the cultural heritages around which civilizations revolve. The following three postulates provide the basis for discussion of a number of themes that demonstrate some important consequences. (i) Information transmission through either pathway has thermodynamic components associated with data storage and transmission. (ii) The semantic content adds no additional thermodynamic cost. (iii) For all semantic exchange, meaning is accessible only through translation and interpretation, and has a value only in context. (1) For both pathways of semantic inheritance, translational and copying machineries are imperfect. As a consequence both pathways are subject to mutation and to evolutionary pressure by selection. Recognition of semantic content as a common component allows an understanding of the relationship between genes and memes, and a reformulation of Universal Darwinism. (2) The emergent properties of life are dependent on a processing of semantic content. The translational steps allow amplification in complexity through combinatorial possibilities in space and time. Amplification depends on the increased potential for complexity opened by 3D interaction specificity of proteins, and on the selection of useful variants by evolution. The initial interpretational steps include protein synthesis, molecular recognition, and catalytic potential that facilitate structural and functional roles. Combinatorial possibilities are extended through interactions of increasing complexity in the temporal dimension. (3) All living things show a behavior that indicates awareness of time, or chronognosis. The ,4 billion years of biological evolution have given rise to forms with increasing sophistication in sensory adaptation. This has been linked to the development of an increasing chronognostic range, and an associated increase in combinatorial complexity. (4) Development of a modern human phenotype and the ability to communicate through language, led to the development of archival storage, and invention of the basic skills, institutions and mechanisms that allowed the evolution of modern civilizations. Combinatorial amplification at the supra-phenotypical level arose from the invention of syntax, grammar, numbers, and the subsequent developments of abstraction in writing, algorithms, etc. The translational machineries of the human mind, the "mutation" of ideas therein, and the "conversations" of our social intercourse, have allowed a limited set of symbolic descriptors to evolve into an exponentially expanding semantic heritage. (5) The three postulates above open interesting epistemological questions. An understanding of topics such dualism, the élan vital, the status of hypothesis in science, memetics, the nature of consciousness, the role of semantic processing in the survival of societies, and Popper's three worlds, require recognition of an insubstantial component. By recognizing a necessary linkage between semantic content and a physical machinery, we can bring these perennial problems into the framework of a realistic philosophy. It is suggested, following Popper, that the ,4 billion years of evolution of the biosphere represents an exploration of the nature of reality at the physicochemical level, which, together with the conscious extension of this exploration through science and culture, provides a firm epistemological underpinning for such a philosophy. © 2007 Wiley Periodicals, Inc. Complexity, 2007 [source] | |||||||||||||