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An Introduction to Astrobiology
Abstract
A textbook designed for introductory university courses in astrobiology. It provides a detailed examination of how life may have arisen on Earth and looks at fossil evidence of early life. The evidence for possible life on Mars is reviewed in detail and the potential for life on Europa and Titan is also examined. The possibility of life in exoplanetary systems is considered and the book concludes with a discussion of the search for extraterrestrial intelligence.
... La principal condiciíon para la presencia de agua líquida es la temperatura superficial del objeto, que en este caso debe estar entre 273K y 373K. A presiones muy bajas, el agua se sublimaría en vapor de agua (Gilmour & Sephton, 2004). ...
... Por lo tanto, una zona habitable circumestelar es definida como el rango de distancias que existe entre una estrella y un planeta para que pueda existir agua líquida en su superficie (Gilmour & Sephton, 2004). Esta zona habitable circumestelar es de gran importancia, puesto que es donde se encuentra el balance entre la radiación solar y la emisión térmica del planeta. ...
Usando un nuevo diagrama de diagnóstico, utilizando el Potencial Gravitacional Bariónico (PGB) como parámetro físico, clasificamos una muestra de 340 de exoplanetas en términos de sus posibles estructuras físicas. Se pudo demostrar que la mayoría de los exoplanetas tienen estructuras similares a los planetas del Sistema Solar. También se mostró que el PGB mismo puede servir de modelo físico para explicar las diferentes relaciones Masa-Radio (MR) de exoplanetas con diferentes estructuras físicas. El beneficio de este nuevo modelo es que explica el comportamiento de cualquier tipo de exoplanetas, tipo Tierra y Super-Tierra, tipo Urano y Neptuno, y tipo Saturno. Incluso nuestro modelo explica el comportamiento de los exoplanetas que sufren inflación de su radio, debido a la irradiación de su estrella, los Júpiter Calientes ``Hot-Jupiters''. Usando el PGB definimos un nuevo límite en masa y radio para exoplanetas que distingue exoplanetas autogravitante (SG) de exoplanetas no autogravitantes (No-SG). Asimismo, mostramos que estos dos tipos de exoplanetas siguen diferentes relaciones MR. Los exoplanetas No-SG tienen un radio que aumenta con la masa, mientras que en los exoplanetas SG el radio se queda constante a medida que la masa aumenta. Revisando la literatura, se encontró que su relación MR es característica de un cierto tipo de composición, lo que sugiere que estos cuerpos están formados de un núcleo sólido y de una envolvente masiva hecha de hidrógeno líquido metálico (HLM). Por lo tanto, nuestro análisis permitió descubrir un nuevo tipo de exoplanetas. Además, comparamos en el diagrama de diagnóstico, las enanas marrón (BDs) con los exoplanetas, usando una muestra de 17 BDs confirmadas. Encontramos una relación MR distinta a la de los exoplanetas, en donde el radio de las BDs disminuye con la masa. Por otro lado, 11 exoplanetas identificados en el diagrama de diagnóstico como candidatas BDs, mostraron la misma relación MR a los BDs. A partir de estos resultados concluimos que los exoplanetas y las BDs tienen diferentes estructuras físicas: las BDs están completamente hechas de gas, mientras los exoplanetas están generalmente compuestos de un núcleo sólido, el cual es cubierto de una envolvente de gas. Esto reafirmó la idea que las BDs y los exoplanetas se forman de manera diferente. En este caso, las BDs podrían ser formadas por el colapso gravitacional de una nube molecular, mientras los exoplanetas se podrían formar mediante la acreción de materia en un disco protoplanetario. Así que, en base al análisis hecho en esta tesis, concluimos que el diagrama de diagnóstico y el modelo de la relación MR, ambos basados en el PGB, son dos herramientas importantes y útiles, que permiten mejorar de manera significativa nuestro conocimiento de la estructuras y origen de los exoplanetas.
... On Mars, the subsurface is protected from strong radiation, UV light, and particle bombardment, and it is thus more favorable than the surface environment for the detection of putative biomolecules (Rothery et al., 2004;Hanslmeier et al., 2012;Fernández-Remolar et al., 2013). Therefore, a comprehensive understanding of lipid preservation in buried evaporite deposits could be of great importance in the detection of past or present biosignatures on Mars. ...
Qaidam Basin (Tibetan Plateau) is considered an applicable analogue to Mars with regard to sustained extreme aridity and abundant evaporites. To investigate the possibility of the preservation of microbial lipids under these Mars analog conditions, we conducted a mineralogical and organic geochemistry study on samples collected from two Quaternary sections in Dalangtan Playa, northwestern Qaidam Basin, which will enhance our understanding of the potential preservation of molecular biomarkers on Mars. Two sedimentary units were identified along two profiles: one salt unit characterized by a predominance of gypsum and halite, and one detrital unit with a decrease of gypsum and halite and enrichment in siliciclastic minerals. Bacterial fatty acids and archaeal acyclic diether and tetraether membrane lipids were detected, and they varied throughout the sections in concentration and abundance. Bacterial and archaeal biomolecules indicate a dominance of Gram-positive bacteria and halophilic archaea in this hypersaline ecosystem that is similar to those in other hypersaline environments. Furthermore, the abundance of bacterial lipids decreases with the increase of salinity, whereas archaeal lipids showed a reverse trend. The detection of microbial lipids in hypersaline environments would indicate, for example on Mars, a high potential for the detection of microbial biomarkers in evaporites over geological timescales. Key Words: Dalangtan playa-The Qaidam Basin-Subsurface evaporites-Lipid biomarkers-Mars. Astrobiology 17, xxx-xxx.
... Iconic traces such as burrows, footprints and coprolites have widely been ignored in the field of astrobiology, with only a few exceptions (Baucon et al., 2015;Hasiotis et al., 2002Hasiotis et al., , 2006). Although biogenic sediment fabrics are regularly listed among the major categories of biosignatures (e.g., DesMarais and Walter, 1999;Sephton, 2004;Westall et al., 2015), sediment mixing by organisms (bioturbation;Bromley, 1996) has received little attention in the astrobiological literature. The only products of organism-substrate interactions that captured some astrobiological attention are microbially induced sedimentary structures (e.g.,Brake and Hasiotis, 2008;Noffke, 2015;Noffke et al., 2013) and microbioerosional structures (e.g.,Buijs et al., 2004;Fisk et al., 2006;Friedmann and Weed, 1987;Slater, 2009;Sugawara et al., 2014;White et al., 2014). ...
Organism-substrate interactions and their products – biogenic structures – are important biosignatures on Earth. This study discusses the application of ichnology – the study of organism-substrate interactions – to the search for present and past life beyond Earth. Three main questions are addressed: (1) Why to look for biogenic structures (i.e. traces and ichnofabrics) beyond Earth? (2) What biogenic structures to expect on other planets, moons and asteroids? (3) How to study extraterrestrial biogenic structures?
... In addition to Mars, other possible targets in the search for extraterrestrial life include the icy moons of Jupiter (Europa) and Saturn (Enceladus) [104]. Our next investigation will be a study of the viability of F. hygrometrica spores and T. squarrosa under the environmental conditions reported for these extraterrestrial moons. ...
The principal goal of astrobiology is the search for extraterrestrial life forms. A key aspect is the study of the ability of different kinds of terrestrial organisms to support simulated extraterrestrial environmental conditions. Mosses are multicellular green plants, poorly studied from an astrobiological perspective. In this paper, we report experimental results obtained using two species of moss, which demonstrate that both the spores of the moss Funaria hygrometrica as well as the desiccated vegetative gametophyte shoots of the moss Tortella squarrosa (Pleurochaete squarrosa) were capable of resisting Simulated Martian Environmental Conditions (SMEC): Mars simulated atmospheric composition 99.9% CO2, and 0.6% H2O with a pressure of 7 mbars, -73 oC and UV irradiation of 30 mW cm-2 in a wavelength range of 200-400 nm under a limited short time of exposition of 2 hours. After being exposed to SMEC and then transferred to an appropriate growth medium, the F. hygrometrica spores germinated, producing typical gametophyte protonemal cells and leafy shoots. Likewise, detached leaves from SMEC-exposed gametophyte shoots of T. squarrosa retained the ability to produce new protonemata and shoots under suitable growth conditions. Furthermore, we studied the tolerance of these moss structures to a thermal stress of 100 °C for 1 h; in both cases the spores and shoots were capable of resisting this heat treatment. Our study using FT-Raman and FT-IR vibrational spectroscopy demonstrated that neither spores nor shoots apparently suffered significant damage in their biomolecular makeup after being subject to these stress treatments. The implications of these findings for the search of life on Mars are discussed.
... Another way of estimating the relative abundances of sulphur to oxygen-bearing species, better suited to 67P, is to consider the observed abundance ratios for similar systems, such as H 2 CO/H 2 CS ∼ 55, CO 2 /CS 2 ∼ 60, and CO/CS ∼ 80 in comet Hale-Bopp (Bockelée-Morvan et al. 2000). These values are in perfect agreement with the O/S value of 55 recommended by Gilmour & Sephton (2004) in their introduction to astrobiology. Another point to consider in regard to the non-detection of sulphur containing compounds in comet 67P is the limitation of the COSAC instrument itself, i.e. the low resolution, meaning that single mass peaks cannot be resolved into different molecular species and that for mass/charge ratios (m/z) over 62, the signals could not be extracted from the background noise (Goesmann et al. 2015 ). ...
Context. The results of an observational search for gas phase urea, (NH 2) 2 CO toward the Sgr B2-LMH region, have been reported recently. In spite of strong presumptions, whether it is urea or another species (for example an isomer) seems to remain a pending question. Aims. In this note, we consider the energetic aspect of this would-be detection by addressing the relative stabilities of the 22 isomers that can possibly be formed with the CH 4 N 2 O set of atoms. By extension, we also consider the 22 sulphur analogues of CH 4 N 2 S chemical formula. Methods. The question was first addressed by means of quantum density functional theory (DFT) simulations. The hybrid B3LYP functional was used throughout. The geometries of the 44 molecules part of this survey were fully optimized and verified to be real minima by vibrational analysis. The lowest isomers found this way were then reconsidered in higher level post Hartree-Fock MP2 and coupled cluster CCSD and CCSD(T) calculations to derive more accurate energy differences and dipole moments, whose knowledge is crucial for interpreting micro-and millimetre-wave spectra. Results. We found that urea and thio-urea are the most stable compounds in their respective families. The closest isomers on the energy scale are the iminol tautomeric forms, HN=COH-NH 2 and HN=CSH-NH 2 , whose rotational constants and dipole moments have also been determined. Conclusions. That urea is the lowest energy isomer possibly formed is a strong argument making the detection of this species more than probable. After formamide and acetamide, this result confirms the greatest stability of the-[NH-C=O]-linkage, underlining the interest of the minimum energy criterion as a tool for the primary search of target molecules. Additionally, thio-urea should the analogue to search for.
... Since 1995, we are in the period which is more and more often referred to as "astrobiological revolution" (e.g. Des Marais and Walter 1999, Grinspoon 2003, Gilmour and Sephton 2004, Chyba and Hand 2005. Rapid increase of our knowledge about the cosmic context of abiogenesis and evolution, as well as realization that there are numerous potential habitats for life in the Galaxy, have been accompanied by the increase in both public interest and institutional framework, including new research departments, new peer-reviewed journals, etc. Entirely new key concepts, such as the Galactic Habitable Zone (henceforth GHZ, Lineweaver 2001, Gonzalez, Brownlee, and Ward 2001, Gonzalez 2005, have been introduced in this period, and the wider synergy between various fields of astronomical and life sciences has been achieved within this wide astrobiological front. ...
We review the history and status of the famous classification of
extraterrestrial civilizations given by the great Russian astrophysicist
Nikolai Semenovich Kardashev, roughly half a century after it has been
proposed. While Kardashev's classification (or Kardashev's scale) has often
been seen as oversimplified, and multiple improvements, refinements, and
alternatives to it have been suggested, it is still one of the major tools for
serious theoretical investigation of SETI issues. During these 50+ years,
several attempts at modifying or reforming the classification have been made;
we review some of them here, together with presenting some of the scenarios
which present difficulties to the standard version. Recent results in both
theoretical and observational SETI studies, especially the G-hat infrared
survey (2014-2015), have persuasively shown that the emphasis on detectability
inherent in Kardashev's classification obtains new significance and freshness.
Several new movements and conceptual frameworks, such as the Dysonian SETI,
tally extremely well with these developments. So, the apparent simplicity of
the classification is highly deceptive: Kardashev's work offers a wealth of
still insufficiently studied methodological and epistemological ramifications
and it remains, in both letter and spirit, perhaps the worthiest legacy of the
SETI "founding fathers".
... We do not know if these conditions are necessary in any case for life to emerge, but we know that they were essential for the appearance and development of life on Earth. By analogy, we will concentrate on these three conditions: (1) the presence of liquid water; (2) the presence of carbon; (3) a source of energy [1, 2]. The presence of liquid water is favored because this molecule, very abundant in the Universe, has several interesting properties: its dipole moment makes it a very active solvent, allowing complex chemical reactions to take place (leading, in particular, to the formation of membranes); water is liquid over a large temperature range; moreover, its solid phase is lighter than the liquid, which makes possible the formation of an icy cover atop the ocean, protecting it in case of glaciation. ...
What are the planetary environments where conditions are best suited for habitability? A first constraint is provided by the presence of liquid water. This condition allows us to define two kinds of media: (1) the atmospheres of solid (exo) planets with a temperature typically ranging between 0 degrees C and 100 degrees C, and (2) the interiors of icy bodies (outer satellites or possibly exosatellites) where the pressure and temperature would fit the liquid phase region of the water phase diagram. In the case of Mars, significant progress has been achieved about our understanding of the history of liquid water in the past, thanks to the findings of recent space missions. The study of the outer satellites is also benefiting from the on-going operation of the Cassini mission. In the case of exoplanets, new discoveries are continuously reported, especially with the Kepler mission, in operation since 2009. With the emergence of transit spectroscopy, a new phase of exoplanets' exploration has started, their characterization, opening the new field of exoplanetology. In the future, new perspectives appear regarding the exploration of Mars, the giant planets and exoplanets, with the ultimate goal of characterizing the atmospheres of temperate exoplanets.
... Lord Kelvin's counsel [i]). Starting with Stanley Miller's 305 experiments (Miller, 1953) that demonstrated the synthesis of small biomolecules under 306 pre-biological conditions (Bada & Lazcano, 2003Gilmore & Sephton, 2004; Sullivan et al., 2007; Lahav, 1999; Fry, 2000; Deamer, 310 2011); the primary drivers for their emergence were persistently cycling, chemical 311 disequilibria arising from solar irradiations of rotating planetary surfaces (Rothschild, 312 2003; Spitzer & Poolman, 2009; Spitzer, 2013; Stüeken et al., 2013 and their metabolic and regulatory components (Szostak et al., 2001; Luisi, 2006; 316 Solé, 2007; Mann, 2012; Rassmusen et al., 2008; Nandagopal & Elowitz, 2011; 317 Purnick & Weiss, 2009; Kwok, 2010; Noireaux et al., 2011; Schwille, 2011; Benner 318 & Sismour, 2005; Church & Regis, 2012; Gibson et al., 2010; Elowitz & Lim, 2010Pross, 2011Pross, , 2013 Benner, 2010; Trifonov, 2012; Szostak; 322 Spitzer, 2013). ...
Within the overlap of physics, chemistry and biology, complex matter becomes more deeply understood when high level mathematics converts regularities of experimental data into scientific laws, theories, and models (Krakauer et al., 2011. The challenges and scope of theoretical biology. J. Theoret. Biol. 276: 269-276). The simplest kinds of complex biological matter are bacterial cells; they appear complex from a physicochemical standpoint because they are multicomponent, multiphase, biomacromolecularly crowded, and re emergent; the property of re-emergence differentiates biological matter from complex chemical and physical matter. Bacterial cells cannot self-reassemble spontaneously from their biomolecules and biomacromolecules (via non-covalent molecular forces) without the action of external drivers; on Earth, such drivers have been diurnal (cycling) physicochemical gradients, i.e. temperature, water activity, etc. brought about by solar radiation striking the Earth's rotating surface. About 3.5 billion years ago, these cycling gradients drove complex chemical prebiotic soups toward progenotic living states from which extant bacteria evolved (Spitzer and Poolman, 2009; The role of biomacromolecular crowding, ionic strength and physicochemical gradients in the complexities of life's emergence. Microbiol. Mol. Biol. Revs. 73:371-388). Thus there is historical non-equilibrium continuity between complex dead chemical matter and complex living states of bacterial cells. This historical continuity becomes accessible to present-day experimentation, when cycling physicochemical gradients act on dead biomacromolecules obtained from (suitably) killed bacterial populations on a biotic soup of chemicals (Harold, 2005, Molecules into cells: specifying spatial architecture. Microbiol. Mol. Biol. Rev. 69:544-564). The making of biotic soups and recovering living states from them is briefly discussed in terms of novel concepts and experimental possibilities. In principle, emergent living states contingently arise and evolve when cycling physicochemical gradients continuously act on complex chemical mass; once living states become dynamically stabilized, the inevitable process errors of primitive cell cycles become the roots of Darwinian evolution.
... It is often hypothesized that plate tectonics may play a role for the development of life (e.g. Parnell, 2004; Ward & Brownlee, 2000; Gilmour & Sephton, 2004). Also, the idea has been put forth that life itself might be the missing energy source (gained by photosynthesis) helping to produce the granite continents which make Earth so special (Rosing et al., 2006; Dyke et al., 2011). ...
Modelling of geodynamic processes like mantle or core convection has strongly improved over the last two decades thanks to the steady development of numerical codes that tend to incorporate a more and more realistic physics. High-performance parallel computations allow the simulation of complex problems, such as the self-consistent generation of tectonic plates or the formation of planetary magnetic fields. However, the need to perform broad explorations of the parameter space and the large computational demands imposed by the non-linear, multi-scale nature of convection, requires several simplifications, in the domain geometry as well as in the physical complexity of the problem. In this chapter, the authors give an overview of the state-of-the-art convection simulations in planetary mantles, the different models and geometries used, and various methods to simplify the computations.
... At the beginning of each class, students downloaded the slides for the day's lecture and were able to take lecture notes on the computer. The textbooks used to supplement lectures included An Introduction to Astrobiology (Gilmour and Sephton, 2003) and Life in the Universe (Bennett and Shostak, 2007). In addition to these textbooks, supplemental primary literature was assigned to complement each lecture topic. ...
With the field of astrobiology continually evolving, it has become increasingly important to develop and maintain an educational infrastructure for the next generation of astrobiologists. In addition to developing more courses and programs for students, it is essential to monitor the learning experiences and progress of students taking these astrobiology courses. At the University of Florida, a new pilot course in astrobiology was developed that targeted undergraduate students with a wide range of scientific backgrounds. Pre- and post-course surveys along with knowledge assessments were used to evaluate the students' perceived and actual learning experiences. The class incorporated a hybrid teaching platform that included traditional in-person and distance learning technologies. Results indicate that undergraduate students have little prior knowledge of key astrobiology concepts; however, post-course testing demonstrated significant improvements in the students' comprehension of astrobiology. Improvements were not limited to astrobiology knowledge. Assessments revealed that students developed confidence in science writing as well as reading and understanding astrobiology primary literature. Overall, student knowledge of and attitudes toward astrobiological research dramatically increased during this course, which demonstrates the ongoing need for additional astrobiology education programs as well as periodic evaluations of those programs currently underway. Together, these approaches serve to improve the overall learning experiences and perceptions of future astrobiology researchers.
Primitive life – defined as a chemical system capable of transferring its molecular information via self‐replication and also capable of evolving – probably originated about 4 billion years ago from the processing of organic molecules by liquid water. Organic matter might have been formed in the primitive atmosphere from methane or carbon dioxide but also in submarine hydrothermal vents. A large fraction of prebiotic organic material might have been brought by meteoritic and cometary dust grains decelerated by the atmosphere. Strategies to understand the origin of life include the reconstitution in the laboratory of an artificial life capable of self‐reproduction and evolution, the search for fossil traces of life in Archean sediments and the search for another example of natural life beyond the Earth, on Mars, Europa, Titan, Enceladus and exoplanets.
Key Concepts
• Life emerged about 4 billion years ago with organic molecules capable of self‐reproduction and of evolving in liquid water.
• A large fraction of the prebiotic organic material came from space.
• The reconstruction of life in a test tube lacks a simple synthesis of RNA.
• The very early fossil traces of life have been erased.
• The oldest accepted fossil traces of life are 3.45 billion years old.
• Mars harboured large oceans in the past and was, therefore, hospitable to life.
• Life may be present within the Europa's ocean.
• Organic chemistry is universal. Life may, therefore, arise on appropriate extrasolar planets.
The aim of this essay is to analyze the role of quantum mechanics as an inherent characteristic of life. During the last ten years the problem of the origin of life has become an innovative research subject approached by many authors. The essay is divided in to three parts: the first deals with the problem of life from a philosophical and biological perspective. The second presents the conceptual and methodological basis of the essay which is founded on the Information Theory and the Quantum Theory. This basis is then used, in the third part, to discuss the different arguments and conjectures of a quantum origin of life. There are many philosophical views on the problem of life, two of which are especially important at the moment: reductive physicalism and biosystemic emergentism. From a scientific perspective, all the theories and experimental evidences put forward by Biology can be summed up in to two main research themes: the RNA world and the vesicular theory. The RNA world, from a physicalist point of view, maintains that replication is the essence of life while the vesicular theory, founded on biosystemic grounds, believes the essence of life can be found in cellular metabolism. This essay uses the Information Theory to discard the idea of a spontaneous emergency of life through replication. Understanding the nature and basis of quantum mechanics is fundamental in order to be able to comprehend the advantages of using quantum computation to be able increase the probabilities of existence of auto replicative structures. Different arguments are set forth such as the inherence of quantum mechanics to the origin of life. Finally, in order to try to resolve the question of auto replication, three scientific propositions are put forward: Q-life, the quantum combinatory library and the role of algorithms in the origin of genetic language.
For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.
Science fiction is created by and for human beings. By definition it sets characters in times, places, and situations that subtly or overtly involve scientific principles. A science fiction work might take place in Earth’s future, such as with the Star Trek universe. It may occur on worlds other than our own, as near as the Mars of Ray Bradbury’s The Martian Chronicles stories or as remote as the intergalactic regions of E. E. “Doc” Smith’s classic “Lensman” series. Or it could present science-based ideas and challenges in a contemporary (at least for a particular time) setting, like in early television series such as Science Fiction Theatre (1955–1957) or The Outer Limits (1963–1965). As a genre science fiction helps expands our conception of what reality is and humanity’s place in the universe.
Based on the history of astrobiology and astrobiological literature, we explore the possibility and necessity of a Philosophy of Astrobiology, and propose a tentative definition of "Philosophy of Astrobiology" for being considered as a possible sub-discipline of Philosophy of Science, different from Philosophy of Biology. We include a Bibliography for a Philosophy of Astrobiology.
RESUMEN: Tomando como fundamento la historia y literatura astrobiológicas, exploramos la posibilidad y necesidad de una Filosofía de la Astrobiología, proponemos una definición de "Filosofía de la Astrobiología" y su consideración como subdisciplina de la Filosofía de la Ciencia, distinta de la Filoso-fía de la Biología. Incluimos una bibliografía para una Filosofía de la Astrobiología.
The construction of giant telescopes at the beginning of the twentieth century combined with the advent of digital computers and rocket science in the last part of the twentieth century totally changed mankind’s thoughts about how common life, and especially intelligent life, may be in the universe. Our knowledge of the physical size of our universe suddenly exploded in 1925 when the astronomer Edwin Hubble looked through what was then the largest and most powerful telescope (Mt. Wilson Observatory in California) in the world and discovered the existence of galaxies located outside our own Milky Way galaxy (Fig. 1.1a, b). Up to that point in time, most astronomers believed our Milky Way galaxy was itself the whole universe, with nothing existing beyond the most distant stars we could see with our best telescopes.
Primitive life – defined as a chemical system capable of transfering its molecular information via self‐replication and also capable of evolving – probably originated about 4 billion years ago from the processing of organic molecules by liquid water. Organic matter might have been formed in the primitive atmosphere from methane or carbon dioxide but also in submarine hydrothermal vents. A large fraction of prebiotic organic material might have been brought by meteoritic and cometary dust grains decelerated by the atmosphere. Strategies to understand the origin of life include the reconstitution in the laboratory of an artificial life capable of self‐reproduction and evolution, the search for fossil traces of life in Archeaen sediments and the search for another example of natural life beyond the Earth, on Mars, Europa, Titan, Enceladus and exoplanets.
Key Concepts
Life emerged about 4 billion years ago with organic molecules capable of self‐reproduction and of evolving in liquid water.
A large fraction of the prebiotic organic material came from space.
The reconstruction of life in a test tube lacks a simple synthesis of RNA.
The very early fossil traces of life have been erased.
The oldest accepted fossil traces of life are 3.45 billion years old.
Mars harboured large oceans in the past and was therefore hospitable to life.
Life may be present within the Europa's ocean.
Organic chemistry is universal. Life may therefore arise on appropriate extrasolar planets.
Astrobiology is used as an explicit example to illustrate some of the social, political and philosophical problems that have arisen as a result of the current institutionalization of science. The associated funding mechanisms and policies that suffer from overbearing systems of management, bureaucracy and administration and frequently come into direct conflict with the aims and objectives of innovative and bold science initiatives are discussed. The profound changes that are required in science-policy structures to foster and defend both creative freedom and transparency are outlined. Biologically rooted, as well as sociological and political factors are identified that can impede the healthy practice of any multidisciplinary science, and of astrobiology in particular. Solutions and guidelines are offered based on a set of proven operating principles practised by successful multidisciplinary research centres.
Die Trockenresistenz verschiedener hitzeliebender Mikroorganismen zeigte unterschiedliche Ausprägungen
und unterschritt unter den getesteten Bedingungen nach maximal drei Monaten ein
nachweisbares Niveau. Je nach Organismus ergaben sich positive oder negative Abweichungen der
Überlebensraten verglichen mit Beblo et al. (2009), worin sich die Komplexität des Phänomens Trockentoleranz
zeigt. Weiterhin konnte ein positiver Einfluss von genau definierter Trockenlagerung bei
geringer Luftfeuchte auf die Überlebensraten der Testorganismen ermittelt werden, gegenüber einer
Lagerung bei mäßiger Luftfeuchte unter weniger stringent kontrollierten Bedingungen. Die Anwesenheit
von O₂ während Trocknungsvorgang und Lagerung hatte verglichen mit anoxischen Bedingungen
artspezifisch einen absolut tödlichen bis nicht nachweisbaren Effekt. Wurde der Trockenheitsstress
nach Beginn der Lagerung durch osmotischen Stress ersetzt, führte dies zu einem beschleunigten
Abfall der Überlebensrate. Überdies wirkte O₂ unter diesen Bedingungen schädlicher
(bei H. marinus). Eine Erhöhung der Lagertemperatur im Anschluss an den Trocknungsvorgang hatte
einen zunehmend negativen Effekt auf die Überlebensrate, eine Erniedrigung der Lagertemperatur
einen positiven Effekt (bei H. marinus). Ebenso hatte die Wachstumsphase der Zellen eine Auswirkung
auf die Überlebensrate (bei A. fulgidus). Im Gegensatz dazu konnte nach einer bis zu vierwöchigen
Exposition gegenüber Ultrahochvakuum kein negativerer Einfluss auf die Testorganismen festgestellt
werden, als für Trockenheit bei Normaldruck.
Von neun im Vorfeld mit ionisierender Strahlung behandelten Anreicherungen aus marinen Hydrothermalsystemen
erwiesen sich sechs als reproduzierbar strahlungstolerant (in Reinkultur). Weiterhin
gelang es in einem Vorversuch zwei mikrobielle Kulturen aus einer mit ionisierender Strahlung
behandelten Umweltprobe aus dem Umfeld eines schwarzen Rauchers zu gewinnen. Eine dieser
Kulturen erwies sich als reproduzierbar strahlungstolerant. Vergleiche zur Phylogenie anhand der
Sequenz des 16Sr-RNA Gens ergaben, dass es sich bei den erstgenannten sechs Reinkulturen um
Stämme von M. jannaschii, Thermococcus barophilus und Thermococcus gammatolerans handelte.
Bei den letzten beiden handelte es sich in Übereinstimmung mit morphologischen Beobachtungen
um eine der Gattung Staphylothermus nahestehende, aber vermutlich taxonomisch davon zu trennende
Gruppe innerhalb der Desulfurococcaceae und in jedem Fall um Stämme einer neuen Art. Die
Ausprägung der Resistenz nach Exposition gegenüber Gammastrahlung (Co-60) war für alle Isolate mit
oben erwähnter Ausnahme hoch. Die Nachweisgrenze detektierbaren Überlebens (etwa 99,99999 %
Inaktivierung) wurde im Bereich zwischen 10 kGy und mehr als 15 kGy erreicht.
Abschließend konnte ein erster Vorversuch eine Korrelation zwischen auf die Zellen applizierter
Strahlungsdosis und Amplifikationseffizienz von deren DNA herstellen. Dazu wurde das 16SrRNAGen
über qPCR vervielfältigt.
Das zu Staphylothermus verwandte Isolat MEX_P besaß den mikroskopischen Befunden nach einige
morphologische Besonderheiten. Im Lichtmikroskop wiesen die Zellen gelegentlich im Inneren sowie
an ihrer Oberfläche Granula auf und neigten unter suboptimalen Wachstumsbedingungen zur Bildung
von Riesenzellen. In elektronenmikroskopischen Präparaten fanden sich neben archaeentypischen
Flagellen auch Fibern, deren Aussehen zu keinem bekannten archaeellen Zellanhang verwandt
ist, und überdies von Membran und S-layer umschlossene Vesikel. Beide können präparationsbedingte
Artefakte darstellen, bei letzteren ist aber eine viral oder zellulär gesteuerte Produktion
glaubhaft. Daneben besitzt das Isolat einen in Anbetracht seiner phylogenetischen Stellung ungewöhnlich
geordneten S-layer.
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