Auswahl der wissenschaftlichen Literatur zum Thema „Primordial atmosphere“

Context. Planets that form early enough to be embedded in the circumstellar gas disk accumulate thick atmospheres of nebular gas. Models of these atmospheres need to specify the surface luminosity (i.e. energy loss rate) of the planet. This luminosity is usually associated with a continuous inflow of solid bodies, where the gravitational energy released from these bodies is the source of energy. However, if these bodies release energy in the atmosphere instead of at the surface, this assumption might not be justified. Aims. Our aim is to explore the interactions of infalling planetesimals with primordial atmospheres at an embedded phase of evolution. We investigate effects of atmospheric interaction on the planetesimals (mass loss) and the atmosphere (heating/cooling). Methods. We used atmospheric parameters from a snapshot of time-dependent evolution simulations for embedded atmospheres and simulated purely radial, infall events of siliceous planetesimals in a 1D, explicit code. We implemented energy transfer between friction, radiation transfer by the atmosphere and the body, and thermal ablation; this gives us the possibility to examine the effects on the planetesimals and the atmosphere. Results. We find that a significant amount of gravitational energy is indeed dissipated into the atmosphere, especially for larger planetary cores, which consequently cannot contribute to the atmospheric planetary luminosity. Furthermore, we examine that planetesimal infall events for cores, MC > 2M⊕, which actually result in a local cooling of the atmosphere; this is totally in contradiction with the classical model.

Abstract The results of large-scale exoplanet transit surveys indicate that the distribution of small planet radii is likely sculpted by atmospheric loss. Several possible physical mechanisms exist for this loss of primordial atmospheres, each of which produces a different set of observational signatures. In this study, we investigate the impact-driven mode of atmosphere loss via N-body simulations. We compare the results from giant impacts, at a demographic level, to results from another commonly invoked method of atmosphere loss, photoevaporation. Applying two different loss prescriptions to the same sets of planets, we then examine the resulting distributions of planets with retained primordial atmospheres. As a result of this comparison, we identify two new pathways toward discerning the dominant atmospheric-loss mechanism at work. Both of these pathways involve using transit multiplicity as a diagnostic, in examining the results of follow-up atmospheric and radial velocity surveys.

ABSTRACT Recent detection of exoplanets with Earth-like insolation attracts growing interest in how common Earth-like aqua planets are beyond the Solar system. While terrestrial planets are often assumed to capture icy or water-rich planetesimals, a primordial atmosphere of nebular origin itself can produce water through oxidation of the atmospheric hydrogen with oxidizing minerals from incoming planetesimals or the magma ocean. Thermodynamically, normal oxygen buffers produce water comparable in mole number equal to or more than hydrogen. Thus, the primordial atmosphere would likely be highly enriched with water vapour; however, the primordial atmospheres have been always assumed to have the solar abundances. Here we integrate the 1D structure of such an enriched atmosphere of sub-Earths embedded in a protoplanetary disc around an M dwarf of 0.3$\, \mathrm{M}_\odot$ and investigate the effects of water enrichment on the atmospheric properties with focus on water amount. We find that the well-mixed highly enriched atmosphere is more massive by a few orders of magnitude than the solar-abundance atmosphere, and that even a Mars-mass planet can obtain water comparable to the present Earth’s oceans. Although close-in Mars-mass planets likely lose the captured water via disc dispersal and photoevaporation, these results suggest that there are more sub-Earths with Earth-like water contents than previously predicted. How much water terrestrial planets really obtain and retain against subsequent loss, however, depends on efficiencies of water production, mixing in the atmosphere and magma ocean, and photoevaporation, detailed investigation for which should be made in the future.

Abstract Photoevaporation is thought to play an important role in early planetary evolution. In this study, we investigate the diffusion limit of X-ray- and ultraviolet-induced photoevaporation in primordial atmospheres. We find that compositional fractionation resulting from mass loss is more significant than currently recognized, because it is controlled by the conditions at the top of the atmosphere, where particle collisions are less frequent. Such fractionation at the top of the atmosphere develops a compositional gradient that extends downward. The mass outflow eventually reaches a steady state in which the hydrogen loss is diffusion-limited. We derive new analytic expressions for the diffusion-limited mass-loss rate and the crossover mass.

ABSTRACT Recent advances in our understanding of the dynamical history of the Solar system have altered the inferred bombardment history of the Earth during accretion of the Late Veneer, after the Moon-forming impact. We investigate how the bombardment by planetesimals left-over from the terrestrial planet region after terrestrial planet formation, as well as asteroids and comets, affects the evolution of Earth’s early atmosphere. We develop a new statistical code of stochastic bombardment for atmosphere evolution, combining prescriptions for atmosphere loss and volatile delivery derived from hydrodynamic simulations and theory with results from dynamical modelling of realistic populations of impactors. We find that for an initially Earth-like atmosphere, impacts cause moderate atmospheric erosion with stochastic delivery of large asteroids, giving substantial growth (× 10) in a few ${{\ \rm per\ cent}}$ of cases. The exact change in atmosphere mass is inherently stochastic and dependent on the dynamics of the left-over planetesimals. We also consider the dependence on unknowns including the impactor volatile content, finding that the atmosphere is typically completely stripped by especially dry left-over planetesimals ($\lt 0.02 ~ {{\ \rm per\ cent}}$ volatiles). Remarkably, for a wide range of initial atmosphere masses and compositions, the atmosphere converges towards similar final masses and compositions, i.e. initially low-mass atmospheres grow, whereas massive atmospheres deplete. While the final properties are sensitive to the assumed impactor properties, the resulting atmosphere mass is close to that of current Earth. The exception to this is that a large initial atmosphere cannot be eroded to the current mass unless the atmosphere was initially primordial in composition.

Abstract The atmosphere of a terrestrial planet that is replenished with secondary gases should have accumulated hydrogen-rich gas from its protoplanetary disk. Although a giant impact blows off a large fraction of the primordial atmosphere of a terrestrial planet in the late formation stage, the remaining atmosphere can become water-rich via chemical reactions between hydrogen and vaporized core material. We find that a water-rich postimpact atmosphere forms when a basaltic or CI chondrite core is assumed. In contrast, little postimpact water is generated for an enstatite chondrite core. We investigate the X-ray- and UV-driven mass loss from an Earth-mass planet with an impact-induced multicomponent H2–He–H2O atmosphere for Gyr. We show that water is left in the atmosphere of an Earth-mass planet when the low flux of escaping hydrogen cannot drag water upward via collisions. For a water-dominated atmosphere to form, the atmospheric mass fraction of an Earth-mass planet with an oxidizing core after a giant impact must be less than a few times 0.1%. We also find that Earth-mass planets with water-dominated atmospheres can exist at semimajor axes ranging from a few times 0.1 au to a few au around a Sun-like star, depending on the mass-loss efficiency. Such planets are important targets for atmospheric characterization in the era of JWST. Our results indicate that efficient mixing between hydrogen and rocky components during giant impacts can play a role in the production of water in an Earth-mass planet.

ABSTRACT The formation of the Solar system’s terrestrial planets concluded with a period of giant impacts. Previous works examining the volatile loss caused by the impact shock in the moon-forming impact find atmospheric losses of at most 20–30 per cent and essentially no loss of oceans. However, giant impacts also result in thermal heating, which can lead to significant atmospheric escape via a Parker-type wind. Here we show that H2O and other high-mean molecular weight outgassed species can be efficiently lost through this thermal wind if present in a hydrogen-dominated atmosphere, substantially altering the final volatile inventory of terrestrial planets. We demonstrate that a giant impact during terrestrial planet formation can remove several Earth oceans’ worth of H2O, and other heavier volatile species, together with a primordial hydrogen-dominated atmosphere. These results may offer an explanation for the observed depletion in Earth’s light noble gas budget and for its depleted xenon inventory, which suggest that Earth underwent significant atmospheric loss by the end of its accretion. Because planetary embryos are massive enough to accrete primordial hydrogen envelopes and because giant impacts are stochastic and occur concurrently with other early atmospheric evolutionary processes, our results suggest a wide diversity in terrestrial planet volatile budgets.

The Hadean was an enigmatic period in the Earth’s history when ocean formation and the emergence of life may have occurred. However, minimal geological evidence is left from this period. To understand the primordial ocean’s composition, we focused on the ocean’s formation processes from CO2- and HCl-bearing water vapor in the high-temperature atmosphere. When the temperature of the lower atmosphere fell below the critical point, high-temperature rain reached the ground surface. Then, hydrothermal reactions between the subcritical fluid and primordial crust started. Eventually, a liquid ocean emerged on the completely altered crust as the temperature decreased to approximately 25 °C. Here, we conducted two experiments and modeling to simulate the reactions of hypothetical primordial crustal rock (basalt or komatiite). The results indicate that the primordial ocean was mildly acidic and rich in CO2, Mg, and Ca relative to Na, irrespective of the rock type, which is different from the modern equivalents. Therefore, unlike the present seawater, the primordial seawater could have been carbonic, bitter, and harsh rather than salty.

L'origine des éléments volatils de la Terre, cruciale pour comprendre l'évolution du Système Solaire primitif, la formation de la Terre et la vie, reste débattue. Les gaz nobles, en raison de leur inertie et de leur grande volatilité, servent de traceurs clés pour les principaux volatils tels que le CO2 et le H2O dans le manteau.Les signatures des gaz nobles dans les panaches mantelliques, en particulier ceux des Galapagos, d'Hawaï et d'Islande, suggèrent un néon de type solaire acquis lors de la formation de la Terre. Deux modèles principaux expliquent l'origine du néon dans le manteau : (i) Le néon a été incorporé dans un océan de magma à partir d'une atmosphère primaire riche en H et He, capturée par gravité. (ii) Le néon a été acquis sur des poussières irradiées par le vent solaire Soleil et incorporées dans des planétésimaux avant l'accrétion de la Terre.La concentration résiduelle des éléments volatils du manteau dans les roches et les minéraux volcaniques est souvent influencée par des processus secondaires plutôt que par les concentrations primaires du manteau. Dans la plupart des basaltes océaniques, la phase volatile est dominée par le CO2. Il est généralement supposé que les concentrations et les rapports isotopiques des gaz nobles dans cette phase sont homogènes à travers les vésicules et dépendent de l'ampleur et du mécanisme de la perte de gaz du magma.Cette thèse présente une recherche pionnière sur des échantillons synthétiques dont les principaux éléments volatils sont le dioxyde de carbone (CO₂) et le néon, en explorant deux conditions de dégazage : (i) Un magma affecté par un apport de gas riche en CO2 et néon.(ii) Un magma où le dégazage est induit par la décompression.La similitude des rapports isotopiques du néon observée dans les échantillons naturel, avec des valeurs intermédiaires entre les valeurs isotopiques solaires et celles de l'implantation du vent solaire, est en accord avec l'hypothèse que le manteau terrestre aurait pu incorporer du gaz issu d'une nébuleuse primordiale lors des premières étapes de la formation de la planète. Néanmoins, cette étude expérimentale présente des preuves convaincantes que le fractionnement isotopique peut se produire à différents stades de l'évolution des vésicules dans le magma, suggérant que les valeurs élevées des rapports isotopiques du néon dans les échantillons naturels doivent être interprétées avec prudence. Nous ne concluons qu'aucun des deux scénarios d'acquisition des volatils légers ne peut être pour l'instant rejeté
The origin of Earth's volatile elements, crucial for understanding the evolution of the early Solar System, Earth's formation, and life, remains debated. Noble gases, due to their inertness and high volatility, serve as key tracers for major volatiles like CO2 and H2O in the mantle.The noble gas signatures in mantle plumes, particularly from Galapagos, Hawaii, and Iceland, suggest a solar-type neon acquired during Earth's formation. Two main models explain neon's origin in the mantle : (i) The neon was incorporated into a magma ocean through gravitational capture of a dense primary atmosphere, (ii) The neon was acquired from planetesimals irradiated by the early Sun during Earth's accretion. The residual concentration of mantle volatiles in volcanic rocks and minerals is often influenced by secondary processes and does not reflect primary mantle concentrations. In most oceanic basalts, the volatile phase is dominated by CO2. It's generally assumed that noble gas concentrations in this phase are similar between vesicles and depend on the extent and mechanism of gas loss from the magma. This thesis presents pioneering research on synthetic samples whose only volatiles are carbon dioxide (CO₂) and neon by exploring simple models of degassing in a closed system such as : (i) A depleted melt affected by a CO2-rich inputs and (ii) a system where the decompression is initiated. The observed isotopic similarity in natural samples, with values midway between the solar isotopic values and those of solar wind implantation, supports the hypothesis that the Earth's mantle may have captured a primordial nebula during the early stages of the planet's formation. Nevertheless, this experimental study presents compelling evidence that isotopic fractionation can occur during various stages of vesicle evolution in magma, suggesting that high isotopic ratios values in natural samples should be interpreted with caution. We conclude that none of the two scenarios of light-volatile acquisition can be for now rejected

Three investigations are conducted into the physical chemistry of volatiles in the outer solar system and the role of volatiles in icy satellite evolution.

Part I:

The thermodynamic stability of clathrate hydrate is calculated under a wide range of temperature and pressure conditions applicable to solar system problems, using a statistical mechanical theory developed by Van der Waals and Platteeuw (1959) and existing experimental data on properties of clathrate hydrates and their components. At low pressure, dissociation pressures and partition functions (Langmuir constants) for CO clathrate (hydrate) have been predicted using the properties of clathrate containing, as guests, molecules similar to CO. The comparable or higher propensity of CO to incorporate in clathrate relative to N₂ is used to argue for high CO to N₂ ratios in primordial Titan if N₂ were accreted as clathrate. The relative incorporation of noble gases in clathrate from a solar composition gas at low temperatures is calculated, and applied to the case of giant planet atmospheres and icy satellites. It is argued that non-solar but well-constrained noble gas abundances would be measured by Galileo in the Jovian atmosphere if the observed carbon enhancement were due to bombardment of the atmosphere by clathrate-bearing planetesimals sometime after planetary formation. The noble gas abundances of Titan's atmosphere are also predicted under the hypothesis that much of the satellite's methane accreted as clathrate. Double occupancy of clathrate cages by H₂ and CH₄ in contact with a solar composition gas is examined, and it is concluded that potentially important amounts of H₂ may have incorporated in satellites as clathrate. The kinetics of clathrate formation is also examined, and it is suggested that, under thermodynamically appropriate conditions, essentially complete clathration of water ice could have occurred in high pressure nebulae around giant planets but probably not in the outer solar nebula; comets probably did not aggregate as clathrate. At moderate pressures, the phase diagram for methane clathrate hydrate in the presence of 15% ammonia (relative to water) is constructed, and application to the early Titan atmospheric composition is described. The high pressure stability of CH₄, N₂, and mixed CH₄-N₂ clathrate hydrate is calculated; conversion back to water and CH₄ and/or N₂ fluids or solids is predicted for pressures ≳12 kilobars and/or temperatures ≳320 K. The effect of ammonia is to shrink the T-P stability field of clathrate with increasing ammonia concentration. A preliminary phase diagram for the high pressure ammonia-water system is constructed using new data of Johnson et al. (1984). These results imply that 1) clathrate is stable throughout the interior of Oberon- and Rhea-sized icy satellites, and 2) clathrate incorporated in the inner-most icy regions of Titan would have decomposed, perhaps allowing buoyant methane to rise. Brief speculation on the implications of this conclusion for the origin of surficial methane on Titan is given. A list of suggested experiments and observations to test the theory and its predictions is presented.

Part II:

We propose a global Titanic ocean, one to several kilometers deep, the modern composition of which is predominantly ethane. If the ocean is in thermodynamic equilibrium with an atmosphere of 3' (mole fraction) methane then its composition is roughly 70% C₂H₆, 25% CH₄, and 5% N₂. Photochemical models predict that C₂H₆ is the dominant end-product of CH₄ photolysis so that the evolving ocean is both the source and sink for ongoing photolysis. The coexisting atmosphere is compatible with Voyager data. Two consequences are pursued: the interaction of such an ocean with the underlying "bedrock" of Titan (assumed to be water-ice or ammonia hydrate) and with the primarily nitrogen atmosphere. It is concluded that although modest exchange of oceanic hydrocarbons with enclathrated methane in the bedrock can in principle occur, it is unlikely for reasonable regolith depths and probably physically inhibited by the presence of a layer of solid acetylene and complex polymeric hydrocarbons a couple of hundred meters thick at the base of the ocean. However, the surprisingly high solubility of water ice in liquid methane (Rebiai et al., 1983) implies that topographic features on Titan of order 100 meter in height can be eroded away on a time scale ≾10⁹ years; "Karst" topography could be formed. Finally, the large solubility difference of N₂ in methane versus ethane implies that the ocean composition is a strong determinant of atmospheric pressure; a simple radiative model of the Titan atmosphere is employed to demonstrate that significant surface pressure and temperature changes can occur as the oceanic composition evolves with time. The model suggests that the early methane-rich ocean may have been frozen; scenarios for evolution to the present liquid state are discussed.

Part III:

A simple convective cooling model of a primordial, CH₄-NH₃-N₂ Titan atmosphere is constructed, in an effort to understand the fate of volatiles accreted from a gaseous disk ("nebula") surrounding Saturn and released from accreting planetesimals during the satellite's formation. Near-surface temperatures are initially ≳400 K consistent with the large amount of energy supplied to the atmosphere during accretion. As a consequence of accretional heating, the upper mantle of the satellite consists of an ammonia-water liquid, extending to the surface. This "magma ocean" is the primary buffer of atmospheric cooling because it is ≳10 times as massive as the atmosphere. The radiative properties of the atmosphere are assumed independent of frequency and the resulting temperature profile is found to be adiabatic; if the atmosphere contains dark particulates surface temperatures could be lower than calculated here. Three major processes drive the cooling: (1) hydrodynamic escape of gas from the top of the atmosphere, which determines the cooling time scales, (2) atmospheric ablation by high velocity impacts (not modeled in detail here), and (3) formation of clathrate hydrate at the ocean-atmosphere interface, at T ≤ 250 K. Cooling time scales driven by escape are sufficiently long (10⁸-10⁹ years) to allow ~10 bars of N₂ to be produced photochemically from NH₃ in the gas phase (Atreya et al., 1978); however, the abundance of NH₃ at temperatures ≾150 K (where the intermediate photochemical products condense out) is optically thick to the dissociative UV photons. Thus, N₂ formation may proceed primarily by shock heating of the atmosphere during large body impacts, as well as by photochemistry (1) at T < 150 K if intermediate products supersaturate, or (2) in a warm stratosphere, with NH₃ abundance fixed by its tropopause value. The clathrate formed during late stages of cooling sequesters primarily CH₄, with some N₂, and forces surface temperatures and pressures to drop rapidly. The clathrate is only marginally buoyant relative to the coexisting ammonia-water liquid. If it sinks, the atmosphere is driven to an N₂-rich state with most of the methane sequestered in clathrate when the ocean surface freezes over at ~180 K. Implications of this scenario for the present surface state of Titan are contrasted with those obtained if the clathrate forms a buoyant crust at the surface.

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.Although the second most abundant element in the cosmos is helium, noble gases are also called rare gases. The reason is that they are not abundant on terrestrial planets like our Earth, which is characterized by orders of magnitude depletion of—particularly light—noble gases when compared to the cosmic element abundance pattern. Indeed, such geochemical depletion and enrichment processes make noble gases so versatile concerning planetary formation and evolution: When our solar system formed, the first small grains started to adsorb small amounts of noble gases from the protosolar nebula, resulting in depletion of light He and Ne when compared to heavy noble gases Ar, Kr, and Xe: the so-called planetary type abundance pattern. Subsequent flash heating of the first small mm to cm-sized objects (chondrules and calcium, aluminum rich inclusions) resulted in further depletion, as well as heating—and occasionally differentiation—on small planetesimals, which were precursors of larger planets and which we still find in the asteroid belt today from where we get rocky fragments in form of meteorites. In most primitive meteorites, we even can find tiny rare grains that are older than our solar system and condensed billions of years ago in circumstellar atmospheres of, for example, red giant stars. These grains are characterized by nucleosynthetic anomalies and particularly identified by noble gases, for example, so-called s-process xenon.While planetesimals acquired a depleted noble gas component strongly fractionated in favor of heavy noble gases, the sun and also gas giants like Jupiter attracted a much larger amount of gas from the protosolar nebula by gravitational capture. This resulted in a cosmic or “solar type” abundance pattern, containing the full complement of light noble gases. Contrary to Jupiter or the sun, terrestrial planets accreted from planetesimals with only minor contributions from the protosolar nebula, which explains their high degree of depletion and basically “planetary” elemental abundance pattern. Indeed this depletion enables another tool to be applied in noble gas geo- and cosmochemistry: ingrowth of radiogenic nuclides. Due to heavy depletion of primordial nuclides like 36Ar and 130Xe, radiogenic ingrowth of 40Ar by 40K decay, 129Xe by 129I decay, or fission Xe from 238U or 244Pu decay are precisely measurable, and allow insight in the chronology of fractionation of lithophile parent nuclides and atmophile noble gas daughters, mainly caused by mantle degassing and formation of the atmosphere.Already the dominance of 40Ar in the terrestrial atmosphere allowed C. F v. Weizsäcker to conclude that most of the terrestrial atmosphere originated by degassing of the solid Earth, which is an ongoing process today at mid ocean ridges, where primordial helium leaves the lithosphere for the first time. Mantle degassing was much more massive in the past; in fact, most of the terrestrial atmosphere formed during the first 100 million years of Earth´s history, and was completed at about the same time when the terrestrial core formed and accretion was terminated by a giant impact that also formed our moon. However, before that time, somehow also tiny amounts of solar noble gases managed to find their way into the mantle, presumably by solar wind irradiation of small planetesimals or dust accreting to Earth. While the moon-forming impact likely dissipated the primordial atmosphere, today´s atmosphere originated by mantle degassing and a late veneer with asteroidal and possibly cometary contributions. As other atmophile elements behave similar to noble gases, they also trace the origin of major volatiles on Earth, for example, water, nitrogen, sulfur, and carbon.

The book explains the key notions and fundamental processes in the dynamics of the fluid envelopes of the Earth (transposable to other planets), and methods of their analysis, from the unifying viewpoint of rotating shallow-water model (RSW). The model, in its one- or two-layer versions, plays a distinguished role in geophysical fluid dynamics, having been used for around a century for conceptual understanding of various phenomena, for elaboration of approaches and methods, to be applied later in more complete models, for development and testing of numerical codes and schemes of data assimilations, and many other purposes. Principles of modelling of large-scale atmospheric and oceanic flows, and corresponding approximations, are explained and it is shown how single- and multi-layer versions of RSW arise from the primitive equations by vertical averaging, and how further time-averaging produces celebrated quasi-geostrophic reductions of the model. Key concepts of geophysical fluid dynamics are exposed and interpreted in RSW terms, and fundamentals of vortex and wave dynamics are explained in Part 1 of the book, which is supplied with exercises and can be used as a textbook. Solutions of the problems are available at Editorial Office by request. In-depth treatment of dynamical processes, with special accent on the primordial process of geostrophic adjustment, on instabilities in geophysical flows, vortex and wave turbulence and on nonlinear wave interactions follows in Part 2. Recently arisen new approaches in, and applications of RSW, including moist-convective processes constitute Part 3.

We are lucky, on Earth. We are lucky because we—as complex and self-aware organisms—are here. We are sustained, given air to breathe, and water, and food, by a very ancient planet: a planet past its midpoint, a planet that is nearer death than birth. Our species is a latecomer. It took some three billion years to bridge the gap from a single-celled organism (originating in this planet’s youth) to a multicellular one, and then a little over half a billion more to arrive at the diversity of species on Earth today, including Homo sapiens . In all this time, the chain of life has remained unbroken. The Earth has been consistently habitable, with an atmosphere, and land, and oceans. Since life began, our planet has never been truly deep-frozen, nor have the oceans boiled away. The Earth is the Goldilocks planet. One recalls, here, the children’s story, where the young heroine of that name walks into the house of the three bears, and in their absence tries out successively their bowls of porridge, their chairs, and their beds. Each time the first and second choices are too hot or cold, large or small, hard or soft—and the third choice is just right . The Earth has been, so far and all in all, just right for life: not just right at any one time, but continuously so for three billion years. There have, though, been some close calls: times of mass extinction. But, life has always clung on to bloom once more. That makes the Earth’s history more remarkable than any children’s story. Other planets have not been so lucky. Mars seems to have been a planet with an appreciable atmosphere, and—at least intermittently—running water over its surface, and may even have begun to incubate life. But the atmosphere was stripped away by the solar wind. Its early lakes and rivers became acid, charged with sulphates. Then, most of the water evaporated and was carried off into space; what little was left became locked away as permafrost and in thin ice-caps. Mars does have weather, including spectacular, planet-wide dust-storms.

The atmosphere of a building is the pervading mood it provides, and can be considered a non-Gibsonian affordance. Atmosphere may frame our experience of a building, but over time our perception of the atmosphere may change. This chapter explores atmosphere in relation to motivation and emotion and the role of the limbic system of the brain. Emotion builds on a set of primordial emotions, but human cognition adds subtlety and supports aesthetic emotions. Paintings by Turner and Constable are examined to take the reader beyond the phenomenology of atmosphere and to explore the idea that the artist “inverts” vision. A visual pathway judges the emerging sketch; a visuomotor pathway updates the sketch. In iterating the process, the sketch changes, but so too will the mental image. An fMRI study of architects observing images of “contemplative” building grounds a critique that suggests challenges for designing further experiments. A crucial obstacle is the distance between cog/neuroscience experiments that seek to isolate the influence of a few key variables and the whole-person experience of using and contemplating a building in all its varied complexity.

Abstract It is difficult to imagine the earth as a young world devoid of all life. The famous Walt Disney cartoon Fantasia gives as good a picture as any of what our prebiotic planet must have been like. The scientific imagination has managed to add some bones to Hollywood’s speculations, in the form of experiments on mixtures of gases that are thought to have constituted the earth’s primordial atmosphere.

Abstract As physical scientists, we are concerned with the behaviour of matter in all its forms. We want to know what matter does and why. This is our goal in studying the primordial universe, the tenuous interstellar medium, the gaseous atmosphere of the Earth, the ionized plasma of the Sun’s corona, the mundane liquids and solids of our human surroundings, and the exotic dense matter within a molecule, an atomic nucleus, or a proton. This book is about a tiny subset of this vast range of forms of matter: structured fluids. Structured fluids are liquids, i.e., condensed matter in which the atoms are adjacent but freely mobile on a local scale.

Abstract Except for major short-term perturbations in surface environments caused by a declining flux of impactors, equable conditions for prebiotic evolution could have existed as early as 4.4 GA. The earth is about 4.6 Ga old. At that remote time, known as the Hadean era (fig. 13.1), its surface was very hot as a result of the accretion process, which, according to recent hypotheses, took about a hundred million years: Its temperature, according to recent models, was about 1,500°K. Thus, the surface was molten. The iron-group elements (Fe, Ni, and Co) melted and passed through the lighter silicate molten rocks down beneath the crust in a process known as the iron catastrophe (R. F. Fox, 1988). Gradually the surface, rich in silicates, cooled down as the accretion energy input decreased. Solid rocks started to emerge, forming a thin scum, and a steam atmosphere began to condense and rain down to form the primordial oceans. Surface temperatures at or below l00°C could have developed as many as 4.4 Ga ago (Chang, 1993, 1994).are 3.8-3.9 billion years old, and there is no geological evidence of prebiotic organic chemical processes taking place on the earth’s surface prior to this time. Most of the very old rocks on Earth were transformed geologically by plate tectonics. Moreover, the early craters formed by impactors disappeared through erosion processes. Fortunately, despite the destruction of much of the geological record of primordial Earth, some of this evidence has been preserved and shown to be relevant to the study of the origin of life.

Abstract My ideas about the future of southern writing are intimately bound up with certain qualities it has had in the past, as a result of its origins in a region with a particularly determining history. In order to forecast the future, I shall have to delve rather extensively into this past. I will begin by clarifying remarks about earlier twentieth-century southern poetry that I put forward in “The Poet at Home in the South” (The Southern Review and Modem Literature 1935-1985, Louisiana State University Press, 1988). Dave Smith, in his essay in the present volume, questions whether there is any recognizable distinctiveness among the poets I and others have treated as southern. I will respond to issues he raises. At the heart of my earlier definition was the paradox I had felt in southern poetry from about the time of John Crowe Ransom and Allen Tate through the earlier James Dickey: that the enormous intelligence of such work was expressed largely in aesthetic terms, through the fused elements of irony, or narrative implication, and rhythm and musicality and formal invention. It was a mix that seemed to me analogous to the more extreme version one finds in Edgar Allan Poe, wherein the atmosphere surrounding the death of a beautiful woman was rendered with the most elaborate aesthetic calculation. I tried to locate this paradox of highly sophisticated artistic craft in the service of primordial, diffused (or atmospheric), predominantly emotional motives-hardly ideas-in a geographical region given to atavistic blood allegiances and to rhetoric in defense of indefensible causes.

Sighing is both performative and vital activity, and exemplifies the role of ‘primordial affectivity’ in the organism’s co-creativity with its environment. Emerging from the organism’s ‘cares’, transforming the atmosphere and the affect that initiated it, the sigh is a striking instance of distributed cognition, an action reaching through ancient respiratory processes to the most deliberate forms of self-care. Premodern psychology understood the sigh as an attempt to free the circulation of vital and animal spirits from blockage caused by the overheating of imaginative and estimative faculties when obsessed by the image of a loved object. Contemporary science similarly sees the chief physiological action of the sigh, the opening of air spaces in the lungs, as dynamically engaged with affective experience. In the domain of psychoanalysis, the sigh is a transitional phenomena; it buys time and gives us the time to open up to something new. The sigh relaxes constriction, opening the throat and enabling speech. Hence its vital importance in amorous verse. ‘Le Sigh’ proposes that sighing is the template for the concluding couplet of Shakespeare’s sonnet form. Its innovation is to give us the breathing room to bear our care-full lives.

Ever since life’s debut on the earth, biotic evolution has been a near-balancing act. On virtually every level, competition and cooperation, shifting endlessly between foreground and background, have tugged and teased evolving systems as they have wobbled through time along the edge of chaos. The emergence of cellular life from the world of complex carbon-based chemistry appears to have happened only once in the primordial dreamtime of planet Earth. Scientists base this conjecture on a number of virtually universal distributions of chemical structures and processes across the spectrum of living organisms. Despite their perhaps tenuous hold on life, the earliest cells, primitive bacteria and archea, possessed the keys to the opening of new potential for matter and energy—the capabilities of self-replication, controlled energy transduction, directed locomotion, and the regulation of an internal environment. Out of this cellular Big Bang there arose a totally new force field on planet Earth superimposed over the physical, chemical, and geological, but with tendrils pervading all of those realms. It was the beginning of the biosphere. Life pervaded and began to transform the lithosphere, hydrosphere, and atmosphere. The chapter highlights transitions of prokaryote to eukaryote via endosymbiosis. Also featured are: biofilms, bioluminescence, coral reefs, and ecological succession.