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Comparing stories about the origin, extent, and future of life: an Asian religious perspective
Abstract
Where did we come from? Are we alone? Where are we going? These are the questions that define the field of astrobiology. New discoveries about life on Earth, the increasing numbers of extrasolar planets being identified, and the technologies being developed to locate and characterize Earth-like planets around other stars are continually challenging our views of nature and our connection to the rest of the universe. In this book, philosophers, historians, ethicists, and theologians provide the perspectives of their fields on the research and discoveries of astrobiology. A valuable resource for graduate students and researchers, the book provides an introduction to astrobiology, and explores subjects such as the implications of current origin of life research, the possible discovery of extraterrestrial microbial life, and the possibility of altering the environment of Mars.
In recent decades, powerful telescopes have enabled astrophysicists to uncover startling new worlds and solar systems. An epochal moment came in 1995, when a planet – 51 Pegasi b – was located orbiting a star other than our own sun. Since then, thousands of new planets have followed, and the question of life beyond earth has become one of the principal topics in discussions between science and religion. Attention to this topic has a long history in Christian theology, but has rarely been pursued at any depth. Writing with both passion and precision, Andrew Davison brings his extensive knowledge of Christian thought to bear, drawing particularly on the thought of Thomas Aquinas, as well as his training as a scientist. No book to date better prepares the Christian community for responding to evidence of other life, if it is found. And yet, we do not need to wait for that to have happened before this book shows its worth. In thinking about planets, creatures, and ecosystems beyond our planet, Davison already reinvigorates our theology for the earth.
Chapter 9 explores theoretical and practical implications for meaning and ethics based on previously developed cosmological theories of value and associated worldviews: cosmological reverence, cosmocultural evolution, and the connection-action principle. The cosmological theories of value ascribe various forms and degrees of value and meaning to the universe and to life and intelligence in the context of cosmic evolution—increasing in degree and implications as we move from cosmological reverence to cosmocultural evolution to the connection-action principle. This chapter explores the relevance of “cosmocentric ethics” and the potential meaning of becoming co-creators of a morally creative cosmos that emphasizes respect for relationships, diversity, and creativity. The chapter finishes with an analysis of practical ethical challenges regarding the search for, and potential interaction with, life on Mars and elsewhere.
The late Palaeozoic was marked by significant changes in atmospheric
chemistry and biotic composition. Geochemical models suggest a marked
increase and then decline of atmospheric oxygen and associated shifts in
the concentration of carbon dioxide. Although the actual magnitude of
these changes is uncertain, the pulse of oxygen concentration may have
reached a maximum of 35% and then dropped to 15% (compared with the
present 21%). This oxygen pulse may have influenced the evolution of
major groups of organisms
Doppler measurements from Keck exhibit a sinusoidal periodicity in the
velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m
s-1 and a period of 3.5239 days, which is indicative of a
``51 Peg-like'' planet with a minimum mass (Msini) of 0.62
MJup and a semimajor axis of 0.046 AU. Follow-up photometry
reveals a drop of 0.017 mag at the predicted time (within the errors) of
transit by the companion based on the velocities. This is the first
extrasolar planet observed to transit its star. The radius of the planet
derived from the magnitude of the dimming is 1.42 RJup, which
is consistent with models of irradiated Jupiter-mass planets. The
transit implies that sini>0.993, leading to a true mass of 0.62
MJup for the planet. The resulting mean density of 0.27 g
cm-3 implies that the companion is a gas giant.
A fundamental question in exobiology remains the degree to which
habitats on Venus, past and present, were, or are suitable for life.
This has relevance for assessing the exobiological potential of
extrasolar Venus-like greenhouse planets. In this paper the parameters
of the Venusian surface and atmosphere are considered and the
biochemical adaptations required to survive them are explored in the
light of new information on microbial adaptations to extreme
environments. Neither the pressure (9.5 MPa) nor the high carbon dioxide
concentrations (97%) represent a critical constraint to the evolution of
life on the surface or in the atmosphere. The most significant
constraints to life on the surface are the lack of liquid water and the
temperature (464°C). In the lower and middle cloud layers of Venus,
temperatures drop and water availability increases, generating a more
biologically favorable environment. However, acidity and the problem of
osmoregulation in hygroscopic sulfuric acid clouds become extreme and
probably life-limiting. If it is assumed that these constraints can be
overcome, considerations on the survival of acidophilic sulfate-reducing
chemoautotrophs suspended as aerosols in such an environment show that
Venus does come close to possessing a habitable niche. Conditions on the
surface and in the atmosphere may have been greatly ameliorated on early
Venus and may also be ameliorated on extrasolar planets with early
Venus-like characteristics where temperatures are less extreme and
liquid water is available.
A suite of nickel, cobalt, iron, copper, and zinc containing sulfides are assayed for the promotion of a model carbon fixation reaction with relevance to local reducing environments of the early Earth. The assay tests the promotion of hydrocarboxylation (the Koch reaction) wherein a carboxylic acid is synthesized via carbonyl insertion at a metal-sulfide-bound alkyl group. The experimental conditions are chosen for optimal assay, i.e., high reactant concentrations and pressures (200 MPa) to enhance chemisorption, and high temperature (250°C) to enhance reaction kinetics. All of the metal sulfides studied, with the exception CuS, promote hydrocarboxylation. Two other significant reactions involve the catalytic reduction of CO to form a surface-bound methyl group, detected after nucleophilic attack by nonane thiol to form methyl nonyl sulfide, and the formation of dinonyl sulfide via a similar reaction. Estimation of the catalytic turnover frequencies for each of the metal sulfides with respect to each of the primary reactions reveals that NiS, Ni3S2, and CoS perform comparably to commonly employed industrial catalysts. A positive correlation between the yield of primary product to NiS and Ni3S2 surface areas provides strong evidence that the reactions are surface catalytic in these cases. The sulfides FeS and Fe(1−x)S are unique in that they exhibit evidence of extensive dissolution, thus, complicating interpretation regarding heterogeneous vs. homogeneous catalysis. With the exception of CuS, each of the metal sulfides promotes reactions that mimic key intermediate steps manifest in the mechanistic details of an important autotrophic enzyme, acetyl-CoA synthase. The relatively high temperatures chosen for assaying purposes, however, are incompatible with the accumulation of thioesters. The results of this study support the hypothesis that transition metal sulfides may have provided useful catalytic functionality for geochemical carbon fixation in a prebiotic world (at least intially) devoid of peptide-based enzymes.
One of the most enigmatic steps in Earth’s ancient transition from a lifeless planet to a living world was the process or
processes by which prebiotic organic molecules were selected, concentrated, and organized into the essential macromolecules
of life. More than a half-century of theory and experiment points to the critical roles of mineral surfaces in the assembly
of proteins, lipid bilayers, and genetic polymers. This review considers three aspects of this problem: (1) the self-assembly
of lipids, which may be enhanced in the presence of minerals; (2) the role of minerals in polymerization of amino acids and
nucleic acids; and (3) the selective adsorption of organic species, including chiral molecules, onto mineral surfaces.
The diffusive boundary layers surrounding sessile marine organisms have been implicated in con- trolling an organism's metabolism and growth. We studied boundary layers surrounding hermatypic corals by moni- toring oxygen concentrations on a submillimetric scale. Oxygen concentration within the boundary layers varied from supersaturation during the day to anoxia at night, although the ambient water composition remained con- stant. Detailed mapping and oxygen measurements re- vealed die1 oxygen fluctuations from supersaturation (373% air saturation) in the light to complete oxygen de- pletion at darkness in the massive coral Favia favus. Ex- posure to a 5-cm/s current reduced the boundary layer thickness from 2.44 mm to 1.90 mm, allowing more rapid oxygen exchange across the diffusive boundary layer. Similar patterns were found in the branching coral Sty- lophora pistillata. In massive corals, the thickness of the diffusive boundary layer was negatively correlated with the size of the polyp. We suggest that the distribution of corals in areas of differential turbulence is related to the thickness of the diffusive boundary layers surrounding them.
Experiments exploring the potential catalytic role of iron sulfide at 250°C and elevated pressures (50, 100, and 200 megapascals)
revealed a facile, pressure-enhanced synthesis of organometallic phases formed through the reaction of alkyl thiols and carbon
monoxide with iron sulfide. A suite of organometallic compounds were characterized with ultraviolet-visible and Raman spectroscopy.
The natural synthesis of such compounds is anticipated in present-day and ancient environments wherever reduced hydrothermal
fluids pass through iron sulfide–containing crust. Here, pyruvic acid was synthesized in the presence of such organometallic
phases. These compounds could have provided the prebiotic Earth with critical biochemical functionality.
Interferometric techniques offer two advantages for the detection and analysis of thermal radiation from planets: destructive interference to strongly suppress the stellar emission, and the possibility of high-resolution imaging to resolve planets and distinguish them from dust emission. This paper presents a new interferometric configuration in which the conflicting requirements for these goals are reconciled. It realizes a very strong, broad interference null, so high-resolution fringes can be used while maintaining good suppression of the stellar disk. Complex phase measurement is precluded by the need for destructive interference, but we find that a cross-correlation technique analogous to aperture synthesis can recover true images. When operated 5 AU from the Sun to escape background emission from local zodiacal dust, the interferometer's sensitivity will be limited fundamentally by noise in the photon flux from warm zodiacal dust in the planetary system under observation. In order to scale the interferometer for adequate sensitivity, the 10 μm emission from such dust could be determined early on by a ground-based interferometer. If stars at 10 pc distance have zodiacal clouds like our own, a 50 m long space interferometer with four 1 m elements should see individual planets like the Earth in images taken over 10 hours. Simultaneous infrared spectra of planets like Earth, Venus, Jupiter, and Saturn could be obtained during a 3 month integration, with the sensitivity to detect carbon dioxide, water, and ozone at the levels seen in Earth's spectrum.
How did life on earth originate? Did replication or metabolism come first in the history of life? In this book, Freeman Dyson examines these questions and discusses the two main theories that try to explain how naturally occurring chemicals could organize themselves into living creatures. The majority view is that life began with replicating molecules, the precursors of modern genes. The minority belief is that random populations of molecules evolved metabolic activities before exact replication existed. Dyson analyzes both of these theories with reference to recent important discoveries by geologists and chemists. His main aim is to stimulate experiments that could help to decide which theory is correct. This second edition covers the enormous advances that have been made in biology and geology in the past and the impact they have had on our ideas about how life began. It is a clearly-written, fascinating book that will appeal to anyone interested in the origins of life.
Modern methods and approaches, such as the analysis of molecular sequences to infer evolutionary relationships among organisms, have provided vast new sets of data to further our understanding ofliving organisms, but there remain enigmas in the biological world that will keep scientists working and thinking for decades. Microorganisms by virtue of their small size and almost unbounded diversity provide ample examples of intriguing mysteries that are being challenged with all of the techniques the modern scientific arsenal can provide. One whole arena of this battle to resolve puzzling mysteries about various microorganisms is the almost unbelievable ability of many micro-organisms to live in extreme environments. Whether the challenge is extreme heat, cold, pressure, hyper salinity, alkalinity or acidity, some micro-organisms live now where no life might seem possible. This fascinating state of affairs is the context for this present volume edited by Joseph Seckbach. This Volume is a compilation of many of the especially interesting questions and biological challenges that arise in the consideration of microorganisms in general and the extremophiles in particular.
I have not had time to prepare a formal paper and wish to apologise for this, since I had every intention of doing so and it has only been made impossible by a combination of extremely heavy duties and being ill for several months this year. On the other hand, I understand that a number of you have either read the little essay I wrote recently [Chance and Necessity, Knopf, New York (1971)], or at least heard of it. Therefore, I hope that if those who have read it agree or disagree, you can ask me some questions after this presentation. What I would like to do here, is the following. I have taken a few notes at random, which are, of course, on various subjects that I did discuss in the book, and I would like to emphasise a few points.
Erwin Schrodinger's What is Life? published 60 years ago, influenced much of the development of molecular biology. In this new book Christian De Duve, Nobel Laureate and pioneer of modern cell biology, presents a contemporary response to this classic, providing a sophisticated consideration of the key steps or bottlenecks that constrain the origins and evolution of life. De Duve surveys the entire history of life, including insights into the conditions that may have led to its emergence. He uses as landmarks the many remarkable singularities along the way, such as the single ancestry of all living beings, the universal genetic code, and the monophyletic origin of eukaryotes. The book offers a brief guided tour of biochemistry and phylogeny, from the basic molecular building blocks to the origin of humans. Each successive singularity is introduced in a sequence paralleling the hypothetical development of features and conditions on the primitive earth, explaining how and why each transition to greater complexity occurred.
It is proposed that the first energy source for life is the formation of pyrite from hydrogen sulfide and ferrous ions and that extant energy flows are biochemical derivatives thereof.
▪ Abstract Theoretical calculations, based on both the chemical and isotopic composition of sedimentary rocks, indicate that atmospheric O2 has varied appreciably over Phanerozoic time, with a notable excursion during the Permo-Carboniferous reaching levels as high as 35% O2. This agrees with measurements of the carbon isotopic composition of fossil plants together with experiments and calculations on the effect of O2 on photosynthetic carbon isotope fractionation. The principal cause of the excursion was the rise of large vascular land plants and the consequent increased global burial of organic matter. Higher levels of O2 are consistent with the presence of Permo-Carboniferous giant insects, and preliminary experiments indicate that insect body size can increase with elevated O2. Higher O2 also may have caused more extensive, possibly catastrophic, wildfires. To check this, realistic burning experiments are needed to examine the effects of elevated O2 on fire behavior.
Proteins and nucleic acid are the seemingly inseparable siblings of biochemistry. For several billion years, life has depended on their reciprocity: Proteins are constructed by nucleic acid; nucleic acid reproduces with the help of proteins. But chemists have long been dogged by the idea that at some point in time one of these classes of molecules must have, at least transiently, performed all the functions necessary for nascent life. It's unlikely that proteins and nucleic acid arose simultaneously and immediately began an interconnected dance, says Andrew Pohorille, head of the biomolecular and cellular modeling program at the National Aeronautics & Space Administration's Ames Research Center in Mountain View, Calif., and a professor of chemistry and pharmaceutical chemistry at the University of California, San Francisco. "It's a little bit of an Occam's razor argument." The current reigning theory that deals with this chicken-and-egg paradox is the so-called RNA view of the world. In ...
Autocatalysis in a nonenzymatic, templete-directed condensation has been demonstrated in a system consisting of three oligonucleotides. A simple form of self-replication occurs, albeit only to a small extent: the template T organizes the building blocks Å and B in such a way that condensation can occur, leading to a second template molecule. Such a nonenzymatic process has long been sought, because it is postulated as a sine qua non for prebiotic evolution in theories on the origin of life.
Does there exist, deep within the earth's crust, a second biosphere--
composed of very primitive, thermophilic (heat-loving) bacteria, and
containing more living matter than the entire surface? This idea, first
proposed by the author in the early 1980s, is now supported by a growing
body of evidence. The implications are astonishing: is the deep
biosphere where life originated? Can Mars and other seemingly dead
planets contain deep biospheres? Is there yet another--deeper,
hotter--biosphere within the earth, based on silicon instead of carbon?
This is the first book to explore this very controversial, intriguing
theory.
Life's Solution builds a persuasive case for the predictability of
evolutionary outcomes. The case rests on a remarkable compilation of
examples of convergent evolution, in which two or more lineages have
independently evolved similar structures and functions. The examples
range from the aerodynamics of hovering moths and hummingbirds to the
use of silk by spiders and some insects to capture prey. Going against
the grain of Darwinian orthodoxy, this book is a must read for anyone
grappling with the meaning of evolution and our place in the Universe.
Simon Conway Morris is the Ad Hominen Professor in the Earth Science
Department at the University of Cambridge and a Fellow of St. John's
College and the Royal Society. His research focuses on the study of
constraints on evolution, and the historical processes that lead to the
emergence of complexity, especially with respect to the construction of
the major animal body parts in the Cambrian explosion. Previous books
include The Crucible of Creation (Getty Center for Education in the
Arts, 1999) and co-author of Solnhofen (Cambridge, 1990). Hb ISBN (2003)
0-521-82704-3
Bacterial communities were detected in deep crystalline rock aquifers within the Columbia River Basalt Group (CRB). CRB ground waters contained up to 60 {mu}M dissolved H{sub 2} and autotrophic microorganisms outnumbered heterotrophs. Stable carbon isotope measurements implied that autotrophic methanogenesis dominated this ecosystem and was coupled to the depletion of dissolved inorganic carbon. In laboratory experiments, H{sub 2} a potential energy source for bacteria, was produced by reactions between crushed basalt and anaerobic water. Microcosms containing only crushed basalt and ground water supported microbial growth. These results suggest that the CRB contains a lithoautotrophic microbial ecosystem that is independent of photosynthetic primary production. 38 refs., 4 figs., 3 tabs.
Mars Global Surveyor images, with resolutions as high as 1.5 m pixel, enable characterization of martian channels and valleys at resolutions one to two orders of magnitude better than was previously possible. A major surprise is the near-absence of valleys a few hundred meters wide and narrower. The almost complete absence of fine-scale valleys could be due to lack of precipitation, destruction of small valleys by erosion, or dominance of infiltration over surface runoff. V-shaped valleys with a central channel, such as Nanedi Vallis, provide compelling evidence for sustained or episodic flow of water across the surface. Larger valleys appear to have formed not by headward erosion as a consequence of groundwater sapping but by erosion from water sources upstream of the observed sections. The freshest appearing valleys have triangular cross sections, with talus from opposing walls meeting at the center of the valley. The relations suggest that the width of the valleys is controlled by the depth of incision and the angle of repose of the walls. The flat floors of less fresh-appearing valleys result primarily from later eolian fill. Several discontinuous valleys and lines of craters suggest massive subsurface solution or erosion. The climatic implications of the new images will remain obscure until the cause for the scarcity of fine-scale dissection is better understood.
We present results from a new simulation code that accounts for the evolution of the reservoirs of carbon dioxide on Mars, from its early years to the present. We establish a baseline model parameter set that produces results compatible with the present (i.e., P~=6.5 mbar with permanent CO2 ice cap) for a wide range of initial inventories. We find that the initial inventory of CO2 broadly determines the evolutionary course of the reservoirs of CO2. The reservoirs include the atmosphere, ice cap, adsorbed CO2 in the regolith, and carbonate rocks. We track the evolution of the free inventory: the atmosphere, ice cap and regolith. Simulations begin at 4.53 Gyr before present with a rapid loss of free inventory to space in the early Noachian. Models that assume a relatively small initial inventory (≲5 bar) have pronounced minima in the free inventory of CO2 toward the end of the Noachian. Under baseline parameters, initial inventories below ˜4.5 bar result in a catastrophic loss of the free inventory to space. The current free inventory would be then determined by the balance between outgassing, sputtering losses and chemical weathering following the end of the late bombardment. We call these ``thin'' models. They generically predict small current free inventories in line with expectations of a small present CO2 ice cap. For ``thick'' models, with initial inventories ≳5 bar, a surplus of 300 700 mbar of free CO2 remains during the late-Noachian. The histories of free inventory in time for thick models tend to converge within the last 3.5 Gyr toward a present with an ice cap plus atmospheric inventory of about 100 mbar. For thick models, the convergence is largely due to the effects of chemical weathering, which draws down higher free inventories more rapidly than the low. Thus, thick models have ≳450 mbar carbonate reservoirs, while thin models have ≲200 mbar. Though both thick and thin scenarios can reproduce the current atmospheric pressure, the thick models imply a relatively large current CO2 ice cap and thin models, little or none. While the sublimation of a massive cap at a high obliquity would create a climate swing of greenhouse warming for thick models, under the thin model, mean temperatures and pressures would be essentially unaffected by increases in obliquity.
The objective of this study was to determine the survivability of osmophilic microorganisms in space, as well as examine the DNA breakage in osmophilic cells exposed to solar UV-radiation plus vacuum and to vacuum only. The organisms used were an unidentified species of Synechococcus (Nägeli) that inhabits the evaporitic gypsum-halite crusts that form along the marine intertidal, and an unidentified species of the extremely halophilic genus Haloarcula (designated as isolate G) isolated from a evaporitic NaCl crystal. Because these organisms are desiccation resistant and gypsum-halite as well as NaCl attenuate UV-radiation, we hypothesized that these organisms would survive in the space environment, better than most others. The organisms were exposed to the space environment for 2 weeks while in earth orbit aboard the Biopan facility. Ground controls were tested in a space simulation facility. All samples were compared to unexposed samples. Survivability was determined by plate counts and the most probable number technique. DNA breakage was determined by labeling breaks in the DNA with 32P followed by translation. Results indicate that the osmophilic microbes survived the 2 week exposure. The major cause of cell death was DNA damage. The number of strand breaks in the DNA from vacuum UV exposed cells was greater than the vacuum only exposed cells.
Recent work on anhydrobiosis in invertebrates is reviewed. I introduce definition and classification of cryptobiosis, and review the distinctive features and extremely high stress tolerance of anhydrobiotic invertebrates. Most anhydrobiotic invertebrates have evolved various kinds of behavioral, morphological, physiological and physical adaptations to reduce water loss during induction of anhydrobiosis. Trehalose is known as a common compatible solute in anhydrobiotic organisms from unicellular organisms to invertebrates and higher plants. Trehalose may provide effective protection against desiccation because it has superior biochemical and physicochemical properties for stabilizing membranes and biomolecules including proteins and lipids. Recent work also indicates several possible kinds of molecules involved in induction of anhydrobiosis. The adaptations necessary for successful induction of and recovery from anhydrobiosis vary greatly among taxa of invertebrates. Understanding the diversity of anhydrobiosis in invertebrates would be a key to elucidate evolutionary scenarios in anhydrobiosis.
The question of responsibility to future generations is a distinctively modern ethical problem, which exposes the limits of many modern ethical frameworks. I argue for the theological importance of this ‘limit’, and of the question of responsibility to future generations, drawing on the ultimate/penultimate conceptuality of Dietrich Bonhoeffer’s Ethics. Responsibility to future generations calls for detailed attention to a given situation, in the light of its openness to a future not within our control; and action for the sake of future generations requires a suspension of one’s own judgement on that action. Christian ethics can take responsibility to future generations seriously while (and indeed through) maintaining a critique of attempts to orient action towards an innerworldly future utopia.
From the beginning, social scientists have celebrated the secularization thesis despite the fact that it never was consistent with empirical reality. More than 150 years ago Toajuen'lle pointed out that "the facts by no means accord with [the secularization] theory," and this lack of accord has grown far worse since then. Indeed, the only shred of credibility for the notion that secularization has been taking place has depended on contrasts between now and a bygone Age of Faith. In this essay 1 assemble the work of many recent historians who are unanimous that the Age of Faith is pure nostalgia -that lack of religious participation was, if anything, even more widespread in medieval times than now. Next, 1 demonstrate that there have been no recent religious changes in Christendom that are consistent with the secularization thesis -not even among scientists. I also expand assessment of the secularization doctrine to non-Christian societies showing that not even the highly magical "folk religions" in Asia have shown the slightest declines in response to quite rapid modernization. Final words are offered as secularization is laid to rest.
Outstanding nineteenth and twentieth century developments in the evidence, conceptions, and speculations concerning the origin and basis of life are considered, with special reference to whether primacy in these respects should be attributed to some form of "protoplasm" in general, or of "gene material," or whether neither of these should be considered to have primacy over the other. The author's view, of the gene material's having primacy (first expressed definitively in 1926), is defended. According to this (as it may today be stated), any living thing, stripped of all its nonessentials, must only have (or have forebears which had) the following three faculties: (1) that whereby it can form more bodies after its own pattern; (2) that whereby, in this process, changes, even indefinitely cumulative ones, can occur, which nevertheless allow the changed successors to form more bodies of these still newer types; and (3) that whereby these different kinds of successors can differently and significantly affect...
Recent reports that Jupiter's satellites Europa and Callisto may have ice-covered oceans have fueled speculation that they may be inhabited by living organisms. Gaidos et al. analyze the thermodynamic requirements for life on Europa by analogy with life on Earth today and during past "snowball" Earth episodes. They conclude that nearly all metabolic life-styles on the present Earth will be denied to organisms on Europa and indicate which types of organisms, if any, are most likely to be found there.
ontmorillonite, a clay mineral formed by the weathering of volcanic ash, may have played a central role in the evolution of life. Because of its structure, montmorillonite tends to adsorb organic com- pounds and this contributes to its ability to catalyze a variety of organic reactions critical to scenarios of life's origins. We have shown experimentally that RNA molecules bind efficiently to clays and that montmorillonite can catalyze the formation of longer molecules (oligomers), thus lending support to the RNA world hypothesis. This theory proposes that life based on RNA preceded current life, which is based on DNA and protein.
Whereas amino acids produced by inorganic reactions are equally split
between two mirror-image versions, the amino acids found in living
things are almost universally "left-handed." The origin of this
biological homochirality, as it is called, has been clouded in mystery,
but a group of astronomers may have stumbled on the answer. They found
that the light passing through large parts of the cosmos is sometimes
circularly polarized in one direction. Such radiation can preferentially
destroy one version of the amino acid molecules that form in space along
with other complex organic compounds. A similar occurrence five billion
years ago may have seeded the solar system and the early earth with a
lopsided mix of amino acids, which would have favored one handedness
over the other when life evolved from these organic molecules.
The late Archean atmosphere was probably rich in biologically generated
CH4 and may well have contained a hydrocarbon haze layer
similar to that observed today on Saturn's moon, Titan. Here we present
a detailed model of the photochemistry of haze formation in the early
atmosphere, and we examine the effects of such a haze layer on climate
and ultraviolet radiation. We show that the thickness of the haze layer
was limited by a negative feedback loop: A haze optical depth of more
than ~0.5 in the visible would have produced a strong ``antigreenhouse
effect,'' thereby cooling the surface and slowing the rate at which
CH4 was produced. Given this climatic constraint on its
visible optical depth, the amount of UV shielding provided by the haze
can be estimated from knowledge of the optical properties and size
distribution of the haze particles. Contrary to previous studies [Sagan
and Chyba, 1997], we find that when the finite size of the particles is
taken into account, the amount of UV shielding provided by the haze is
small. Thus NH3 should have been rapidly photolyzed and
should not have been sufficiently abundant to augment the atmospheric
greenhouse effect. We also examine the question of whether
photosynthetically generated O2 could have accumulated
beneath the haze layer. For the model parameters considered here, the
answer is ``no'': The upper limit on ground level O2
concentrations is ~10-6atm, and a more realistic estimate for
pO2 during the late Archean is 10-8atm. The
stability of both O2 and NH3 is sensitive to the
size distribution and optical properties of the haze particles, neither
of which is well known. Further theoretical and laboratory work is
needed to address these uncertainties.
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
Jupiter's satellite Europa has been identified as one of the most likely sites for life in the solar system. The tidal-tectonic processes that appear to have governed Europa's geology seem to require interaction with an ocean under only a very thin crust, providing a variety of evolving environmental niches. The mutually dependent relationship between orbital evolution and tidal processes in turn controls Europa's rotation, heating, and stress. Surface lineaments are correlated with global stress patterns, demonstrating that they form by crustal cracking, but only if a substantial ocean is present to give adequate tidal amplitude. Tidal driving of strike-slip faulting indicates that cracks penetrate to a fluid layer, which is possible only with a very thin ice crust. The characteristic ridge sets that cover tectonic terrain are likely built by tidal pumping of fluid and slush to the surface on a daily basis. Widespread tectonic dilation creates new surface as material rises from below. Chaotic terrain has morphology and other characteristics indicative of melt-through from below. Surface colorants correlate with locations, such as along large-scale ridge systems and around chaotic terrain, where ocean water reached the surface. This model implies that as a result of tides, liquid water regularly bathed crustal cracks and surfaces with heat and whatever nutrients are included in the oceanic chemistry, creating a variety of habitable environments. The processes were recent and thus most likely continue today. Longer-term evolution of environmental conditions provided the need for adaptation and opportunity for evolution.
Ecologically responsible policies are concerned only in part with pollution and resource depletion. There are deeper concerns which touch upon principles of diversity, complexity, autonomy, decentralization, symbiosis, egalitarianism, and classlessness.
ALTHOUGH around 70% of the Earth's surface is marine, little is known about the microbiology of underlying sediments, which can be more than a kilometre deep1. Selective degradation of organic matter within sediments over geological time profoundly affects the chemical composition of the ocean and atmosphere2. Microbial processes have a fundamental role in surface sediments3,4, but despite geochemical evidence5, their significance in deeper sediments has not been established6. Here we report the discovery of viable sediment bacterial populations at five Pacific Ocean sites to depths >500m. Bacterial distributions and activities are commensurate with geochemical changes. Bacterial profiles with depth are remarkably consistent, and deviations can be linked to specific environmental factors. The rate of decline in these populations indicates that bacteria are present to even greater depths.
"Are they worlds, or are they mere masses of matter? Are physical forces alone at work there or has evolution begotten something more complex, something not unakin to what we know on Earth as life? It is in this that lies the peculiar interest of Mars."Percival Lowell (in ref. 1, p. 3)
The discovery of subsurface communities has encouraged speculation that such communities might be present on planetary bodies exposed to harsh surface conditions, including the early Earth. While the astrobiology community has focused on the deep subsurface, near-subsurface environments are unique in that they provide some protection while allowing partial access to photosynthetically active radiation. Previously we identified near-surface microbial communities based on photosynthesis. Here we assess the productivity of such an ecosystem by measuring in
situ carbon fixation rates in an intertidal marine beach through a diurnal cycle, and find them surprisingly productive. Gross fixation along a transect (99×1 m) perpendicular to the shore was highly variable and depended on factors such as moisture and mat type, with a mean of ~41 mg C fixed m−2 day−1. In contrast, an adjacent well-established cyanobacterial mat dominated by Lyngbya
aestuarii was ~12 times as productive (~500 mg C fixed m−2 day−1). Measurements made of the Lyngbya mat at several times per year revealed a correlation between total hours of daylight and gross daily production. From these data, annual gross fixation was estimated for the Lyngbya mat and yielded a value of ~1.3×105 g m−2 yr−1. An analysis of pulse-chase data obtained in the study in conjunction with published literature on similar ecosystems suggests that subsurface interstitial mats may be an overlooked endogenous source of organic carbon, mostly in the form of excreted fixed carbon.
The
Biological
Universe (Dick 1996) analysed the history of the extraterrestrial life debate, documenting how scientists have assessed the chances of life beyond Earth during the 20th century. Here I propose another option – that we may in fact live in a postbiological universe, one that has evolved beyond flesh and blood intelligence to artificial intelligence that is a product of cultural rather than biological evolution. MacGowan & Ordway (1966), Davies (1995) and Shostak (1998), among others, have broached the subject, but the argument has not been given the attention it is due, nor has it been carried to its logical conclusion. This paper argues for the necessity of long-term thinking when contemplating the problem of intelligence in the universe. It provides arguments for a postbiological universe, based on the likely age and lifetimes of technological civilizations and the overriding importance of cultural evolution as an element of cosmic evolution. And it describes the general nature of a postbiological universe and its implications for the search for extraterrestrial intelligence.
A mixture of gases, CH4, NH3, H2O and H2, which possibly made up the atmosphere of the Earth in its early stages, has been subjected to spark and silent discharges for times of the order of a week to determine which organic compounds would be synthesized. Several designs of apparatus and reasons for their construction are described. Analyses of the remaining gases were made and CO, CO2, N2 and the initial gases were found. A red compound that seems to be associated with the trace metals is formed, as well as yellow compounds probably polymers, which have acidic, basic and ampholytic properties. The mixture of compounds is separated into acidic, basic and ampholytic fractions with ion exchange resins. The amino acids are chromatographed on Dowex-50 and the acids on silica. Glycine, d,l-alanine, β-alanine, sarcosine, d,l-α-amino-n-butyric acid and α-aminoisobtityric acid have been identified by paper chromatography and by melting points of derivatives. Substantial quantities of several unidentified amino acids and small amounts of about 25 amino acids are produced, while glycolic, d,l-lactic, formic, acetic and propionic acids make up most of the acid fraction. Quantitative estimates of these compounds are given. Evidence is presented that polyhydroxy compounds of unknown composition are present. HCN and aldehydes are direct products of the discharge. Although there is insuflicient evidence, the synthesis of the hydroxy and amino acids may be through the hydroxy and amino nitriles in the solution. The relation of these experiments to the formation of the Earth and the origin of life is briefly discussed.