Probleme der atmosphärischen Evolution im Präkambrium

Zusammenfassung Infolge des Sauerstoff-Unterschusses im Material von Erdmantel und Erdkruste besitzen deren Entgasungsprodukte generell reduzierenden Charakter und kommen somit als Lieferant von freiem Sauerstoff nicht in Frage. Die Quelle für den Luftsauerstoff muß deshalb in nicht-geologischen Prozessen zu suchen sein, bei denen der Sauerstoff nachträglich aus oxidischen Verbindungen (H₂O, CO₂) freigesetzt wurde. Da als Energiequelle für diese Reaktionen praktisch nur das Sonnenlicht zur Verfügung steht, muß die Anwesenheit von freiem Sauerstoff in der Atmosphäre letztlich auf einem photochemischen Effekt beruhen.Hierbei ist zu unterscheiden zwischen 1. einem anorganischen photochemischen Effekt, der mit dem kurzwelligen (energiereichen) Teil des Sonnenspektrums arbeitet (insbesondere 1500–2100 Å) und 2. einem organischen photochemischen Effekt, der mit dem Spektralbereich des sichtbaren Lichtes arbeitet, aber auf die Mitwirkung eines Katalysators (Chlorophyll) angewiesen ist. Der Anteil des ersteren Prozesses (Photodissoziation von Wasserdampf) am Aufbau der sauerstoffreichen Atmosphäre dürfte bei weitem geringer gewesen sein als der des zweiten (biologische Photosynthese von Kohlehydraten aus CO₂ und H₂O unter Freisetzung von Sauerstoff als Stoffwechselprodukt), so daß der heutige Luftsauerstoff im wesentlichen als biogen gedeutet werden kann. Die geochemische Evolution der Atmosphäre und die Evolution des Lebens sind somit auf das engste miteinander verknüpft. Mit dem Übergang von der primär reduzierenden zur oxidierenden Atmosphäre konnte beim Überschreiten des sog. Pasteur-Punktes (O₂-Partialdruck 10^–2 des heutigen Wertes) der Umschlag vom fermentativen zum oxidativen Energiestoffwechsel erfolgen. Es kann mit guten Gründen angenommen werden, daß die explosive Differenzierung des Lebens an der Wende Präkambrium-Kambrium eine Folge des höheren Energiegewinns bei der Atmung war. Sowohl die Aufrechterhaltung des Lebens als thermodynamisch metastabiler Zustand (mit einer Entropie weit unterhalb des Maximums) als auch seine Differenzierung im Laufe der Evolution bedürfen der ständigen Zufuhr von Energie, sind also nach der bekanntenBoltzmannschen Beziehung im Grunde genommen äußerst unwahrscheinliche Vorgänge. Freier Sauerstoff, der eine vollständige Verbrennung der Kohlehydrate zu Kohlendioxid und Wasser ermöglichte (und damit den Wirkungsgrad des Energiestoffwechsels im Vergleich zur anaeroben Gärung auf etwa das Vierzehnfache erhöhte), spielte bei der Evolution der Metazoen offensichtlich die Rolle Maxwellschen Dämons, der für die Aufrechterhaltung des thermodynamischen Ungleichgewichts (bzw. der Negentropie) in größeren Zellverbänden verantwortlich war.

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Because of the oxygen deficiency within the material of the earth's crust and mantle, degassing of the lithosphere does not furnish free oxygen, but gases possessing a strongly reducing character. Therefore, other than geological sources must have provided the free oxygen forming a major constituent of the present atmosphere. It is reasonable to conclude that this oxygen has been liberated from gaseous oxides such as water vapour and carbon dioxide. Since a large-scale dissociation of these compounds can only be brought about by solar radiation, photochemical activity must be responsible for the presence of molecular oxygen in the earth's atmosphere.In this context, we have to distinguish between 1. an inorganic photochemical process working with the energy-rich short wave-lengths of the solar spectrum (2 between 1500 and 2100 Å) and 2. an organic or biologic photochemical process which utilizes the spectral range of the visible light. In addition, the biologic process requires a porphyrin body (chlorophyll) to be present as a catalyst. The oxygen-producing capacity of the inorganic process, i. e., photodissociation of water vapour, is considerably smaller (about 10^–3) than that of the organic process (photosynthesis of carbohydrates from CO₂ and H₂O, releasing oxygen as a metabolic by-product). Accordingly, the bulk of the oxygen now present in the atmosphere may safely be regarded as being biologic in origin.Thus, the geochemical evolution of the atmosphere and the evolution of life are closely related and interdependent. The rise of the oxygen pressure of the ancient atmosphere to about 10^–2 P.A.L. (Present Atmospheric Level) enabled life to pass thePasteur point and change from fermentative (anaerobic) to respiratory (aerobic) metabolism. There is reason to believe that the appearance of the first metazoan faunas in the Late Precambrian, about 0.7×10⁹ years ago (Nama-Ediacara fauna), was a direct result of the enormous rise in metabolic energies derived from the more efficient aerobic metabolism.Life as a nonequilibrium steady state, being characterized by an entropy far below the level of its surroundings, requires a constant supply with free energy for its maintenance. As may be concluded from the impact of respiration on the diversification of life at the dawn of the Phanerozoic, this diversification was also dependent on an increased supply in free energy. Evolution thus being— just as life itself — an energy-absorbing (endergonic) process, it must be regarded as highly improbable in terms of theBoltzmann theory of thermodynamics. The mechanism of respiration, using oxygen as a final hydrogen acceptor in energyreleasing biologic redox processes (thereby increasing metabolic energies by the factor of fourteen), obviously played the role of the Maxwellian demon which caused the process of evolution to go into the direction of more order (or diversification) and less entropy.

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Résumé Le présent travail donne un aperçu de l'état actuel de nos connaissances concernant l'évolution de l'atmosphère terrestre depuis le Précambrien ancien. La transformation de l'atmosphère primitive réductrice en l'atmosphère actuelle oxydante paraît, pour la plus grande part, être due à des facteurs biologiques. En raison du parallélisme frappant entre l'évolution organique et l'évolution atmosphérique, la Paléontologie revêt une importance particulière pour l'histoire de l'atmosphère terrestre.

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Green clinopyroxenes and associated phases in a potassium-rich lava from the Leucite Hills,Wyoming

Green, salitic pyroxenes occur as megacrysts and as cores in diopsidic pyroxene phenocrysts and microphenocrysts in a wyomingite lava from Hatcher Mesa, Leucite Hills, Wyoming. Al-rich phlogopite (16–21% Al₂O₃), apatite, Fe-Ti-oxide, Mg-rich olivine (Fo₉₃) and orthopyroxene (En₆₁) also occur as megacrysts or as inclusions in diopside phenocrysts. All of these phases are found in ultramafic xenoliths in the host lava, and petrographic and chemical evidence is presented that the megacrysts originate by the disaggregation of the xenoliths. It is concluded that the latter are accidental fragments of the wall rocks traversed by the wyomingite magma and it is suggested that the clinopyroxene-rich xenoliths, from which the green pyroxenes are derived, formed in the upper mantle as a result of local metasomatism or by crystallization from magmas of unknown composition during an earlier igneous event. The precise role of the clinopyroxene-rich xenoliths (which also contain apatite, Fe-Ti-oxide and amphibole) in the genesis of the Leucite Hills magmas cannot be elucidated on the basis of the available data, but it is unlikely that they represent the source material from which these magmas are derived.     

Drivers of change in Brazil’s carbon dioxide emissions

Brazil’s economic development has been underpinned by a diverse and – in a global comparison – unusual set of energy carriers, notably hydroelectricity and ethanol from sugar cane. Its energy mix makes Brazil one of the least energy-related carbon-intensive economies worldwide. Given that the country is fast becoming one of the world’s economic powerhouses, decision-makers need to understand the drivers underlying past and current carbon dioxide emissions trends. We therefore investigate a) which key long-term drivers have led to Brazil’s unique emissions profile, and b) the implications of these drivers for Brazil’s national policies. We show that Brazil’s emissions are growing mainly due to increasing individual standards of living, exports and population size, and that this growth is so far unchallenged by technological and structural improvements toward lower emissions intensities and more efficient production structures. As these trends are likely to continue amidst growing international pressure on key economies to reduce their carbon emissions, a decoupling of drivers from emissions is needed to simultaneously meet development and environmental goals.     

2021 JGS best paper award and the editors’ choice paper volume 24(1)

Journal of Geographical Systems -     

Deep-seated gravitational slope deformation (DSGSD) and slow-moving landslides in the southern Tien Shan Mountains: new insights from InSAR,tectonic and geomorphic analysis

We investigated deep-seated gravitational slope deformation (DSGSD) and slow mass movements in the southern Tien Shan Mountains front using synthetic aperture radar (SAR) time-series data obtained by the ALOS/PALSAR satellite. DSGSD evolves with a variety of geomorphological changes (e.g. valley erosion, incision of slope drainage networks) over time that affect earth surfaces and, therefore, often remain unexplored. We analysed 118 interferograms generated from 20 SAR images that covered about 900 km². To understand the spatial pattern of the slope movements and to identify triggering parameters, we correlated surface dynamics with the tectono-geomorphic processes and lithologic conditions of the active front of the Alai Range. We observed spatially continuous, constant hillslope movements with a downslope speed of approximately 71 mm year⁻¹ velocity. Our findings suggest that the lithological and structural framework defined by protracted deformation was the main controlling factor for sustained relief and, consequently, downslope mass movements. The analysed structures revealed integration of a geological/structural setting with the superposition of Cretaceous–Paleogene alternating carbonatic and clastic sedimentary structures as the substratum for younger, less consolidated sediments. This type of structural setting causes the development of large-scale, gravity-driven DSGSD and slow mass movement. Surface deformations with clear scarps and multiple crest lines triggered planes for large-scale deep mass creeps, and these were related directly to active faults and folds in the geologic structures. Our study offers a new combination of InSAR techniques and structural field observations, along with morphometric and seismologic correlations, to identify and quantify slope instability phenomena along a tectonically active mountain front. These results contribute to an improved natural risk assessment in these structures. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd     

Scientific detector workshop 2022 on-sky performance verification of near-infrared e−APD technology for wavefront sensing and demonstration of e−APD pixel performance to improve the sensitivity of large science focal planes

Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e⁻APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is m_k = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10⁻³ e⁻/s have been demonstrated with 1Kx1K e⁻APD arrays and 2Kx2K e⁻APD arrays have already been developed, the possibilities and adaptations of e⁻APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed.