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Abstract
It is generally accepted within the natural sciences that life emerged on Earth by a kind of proto-Darwinian evolution from molecular assemblies that were predominantly formed from the various constituents of the primitive atmosphere and hydrosphere. Evolutionary stages under discussion are: the self-organization of spontaneously formed biomolecules into early precursors of life (protobionts), their stepwise evolution via (postulated) protocells to (postulated) progenotes and the Darwinian evolution from progenotes to the three kingdoms of contemporary organisms (archaebacteria, eubacteria and eukaryotes). Considerable discrepancies between scientists have arisen because all evolutionary stages from prebiotic molecules to progenotes are entirely hypothetical and so are the postulated environmental conditions. We can only theorize that all those environmental conditions that allow the existence of the various forms of contemporary life might have allowed also the development of their precursors. Because of all these difficulties the hypothesis that life came to our planet from a remote place of our universe (panspermia) has been revived. But experimental evidence only supports the view that spores can--under favorable circumstances--survive a relatively short journey within our solar system (interplanetary transfer of life). It is extremely unlikely that spores can survive a journey of hundreds or thousands of years through interstellar space.
... Speculation on the interplanetary transfer of life predates human spaceflight (e.g., Conan- Doyle, 1912; Dose, 1986). Life on Earth may have evolved from a universal ancestor (Woese, 1998), but there are several theories of origin (Dose, 1986). ...
... Speculation on the interplanetary transfer of life predates human spaceflight (e.g., Conan- Doyle, 1912; Dose, 1986). Life on Earth may have evolved from a universal ancestor (Woese, 1998), but there are several theories of origin (Dose, 1986). Life may have originated on another planet and survived escape, space travel, atmospheric entry, and impact on Earth, where it successfully reproduced (Mileikowsky et al., 2000; Nicholson et al., 2000). ...
The nematode Caenorhabditis elegans, a popular organism for biological studies, is being developed as a model system for space biology. The chemically defined liquid medium, C. elegans Maintenance Medium (CeMM), allows axenic cultivation and automation of experiments that are critical for spaceflight research. To validate CeMM for use during spaceflight, we grew animals using CeMM and standard laboratory conditions onboard STS-107, space shuttle Columbia. Tragically, the Columbia was destroyed while reentering the Earth's atmosphere. During the massive recovery effort, hardware that contained our experiment was found. Live animals were observed in four of the five recovered canisters, which had survived on both types of media. These data demonstrate that CeMM is capable of supporting C. elegans during spaceflight. They also demonstrate that animals can survive a relatively unprotected reentry into the Earth's atmosphere, which has implications with regard to the packaging of living material during space flight, planetary protection, and the interplanetary transfer of life.
... When science progressed, it became clear that creativity is insufficient to deal with the origin of life in a scientifically adequate way, and that rather both (paleontological) field evidence and biological expertise should be used as the most fundamental building stones for theories about this topic. Even this insight left ample space for a variety of theories (Dose, 1986), three of which are still being seriously considered: (1) the dprimordial-soup theoryT (also known as the deprimordial-soup theoryT) hypothesising that life formed by incidental combination of dorganicT molecules formed under the then conditions in the oceans; (2) the dpizza theoryT,Fig. 1 . Primaevifilium amoenum, interpreted as a cellular filamentous prokaryotic microorganism from the Apex Chert (approx. ...
The search for extraterrestrial life was recently intensified because of new space missions. As long as life has not been found elsewhere in the universe, the best chances to discover extraterrestrial life are considered to be in the study of meteorites. The finding of traces of life on meteorites has been claimed several times, but all claims so far have appeared unjustified. One of the problems is that it is not known how possible extraterrestrial life developed, nor on the basis of which chemical, biochemical and energetic basis this may have taken place. It is argued that possible traces of life that differ fundamentally from life on Earth will not be recognized with the knowledge we have nowadays; traces of life that do not differ fundamentally from those on earth will not be recognized as extraterrestrial, either because such life may have originated on Earth (and have made a space trip afterwards), or because life on Earth may have come from the same source from where the life forms on the meteorite were derived. D 2004 Elsevier B.V. All rights reserved.
... Life may have arisen on another planet or moon. But some regard it extremely unlikely that spores could have survived prolonged space travel and rapid entry into our atmosphere (Dose, 1986;Weber and Mayo Greenberg, 1985). Others disagree (Davies, 2001;Secker et al., 1996), citing spore coatings of silicon or carbon (lithopanspermia) as a mechanism of shielding even interstellar organisms from UV radiation, excessive speed, shock, and heat (Melosh, 1993;Weiss et al., 2000). ...
Where and how did the complex genetic instruction set programmed into DNA come into existence? The genetic set may have arisen elsewhere and was transported to the Earth. If not, it arose on the Earth, and became the genetic code in a previous lifeless, physical-chemical world. Even if RNA or DNA were inserted into a lifeless world, they would not contain any genetic instructions unless each nucleotide selection in the sequence was programmed for function. Even then, a predetermined communication system would have had to be in place for any message to be understood at the destination. Transcription and translation would not necessarily have been needed in an RNA world. Ribozymes could have accomplished some of the simpler functions of current protein enzymes. Templating of single RNA strands followed by retemplating back to a sense strand could have occurred. But this process does not explain the derivation of "sense" in any strand. "Sense" means algorithmic function achieved through sequences of certain decision-node switch-settings. These particular primary structures determine secondary and tertiary structures. Each sequence determines minimum-free-energy folding propensities, binding site specificity, and function. Minimal metabolism would be needed for cells to be capable of growth and division. All known metabolism is cybernetic--that is, it is programmatically and algorithmically organized and controlled.
With the development of space technology, exobiology has been established as a scientific discipline. The term ‘exobiology’ was introduced by Lederberg (1960), who recognised the emerging capabilities of space exploration for giving new impetus to biology much as the development of astronomy has broadened our understanding of the physical world and the spectral analysis of the stars has proven the universality of the concepts of chemistry. Classical biological research has concentrated on the only example of life so far known, i.e. life on Earth. In contrast, exobiology extends the boundaries of biological investigations beyond the Earth, to other planets, comets, meteorites, and space at large. To date, the over-riding objective of exobiological research has been to attain a better understanding of the principles leading to the emergence of life from inanimate matter, its evolution, and its distribution on Earth and throughout the Universe (Klein 1986). To reach this goal, exobiological research has focused on the different steps of the evolutionary pathways through cosmic history that may be related to the origin, evolution and distribution of life.
Biological materials and processes inspire many engineered materials and devices because of their specialized nature and oftentimes high efficiency. Although optimized in vivo through hereditary evolution, primordial versions of biological materials must have evolved via chemical routes, and therefore it stands to reason that biomimetic chemistry is complementary to research in chemical evolution. The types of reactions described by Miller-Urey, for example, represent synthetic routes from inorganic gas mixtures to organic molecules that, in turn, serve as a pool of precursors in combinatorial polymerization reactions. On a primordial Earth, these reactions would presumably be subject to a geochemical form of molecular imprinting, which may justify an origin of peptide motifs and enzyme archetypes that preexisted hereditary mechanisms of optimization.
Astronomically, there are viable mechanisms for distributing organic material throughout the Milky Way. Biologically, the
destructive effects of ultraviolet light and cosmic rays means that the majority of organisms arrive broken and dead on a
new world. The likelihood of conventional forms of panspermia must therefore be considered low. However, the information content of damaged biological molecules might serve to seed new life (necropanspermia).
KeywordsRadiation pressure–Cosmic rays–Micro-organisms–Viruses–Information
On board of the NASA Long Duration Exposure Facility (LDEF), spores of Bacillus subtilis in monolayers (106/sample) or multilayers (108/sample) were exposed to the space environment for nearly six years and their survival was analyzed after retrieval. The response to space parameters, such as vacuum (10-6 Pa), solar electromagnetic radiation up to the highly energetic vacuum-ultraviolet range (109 J/m2) and/or cosmic radiation (4.8 Gy), was studied and compared to the results of a simultaneously running ground control experiment. If shielded against solar ultraviolet (UV)-radiation, up to 80 % of spores in multilayers survive in space. Solar UV-radiation, being the most deleterious parameter of space, reduces survival by 4 orders of magnitude or more. However, up to 104 viable spores were still recovered, even in completely unprotected samples. Substances, such as glucose or buffer salts serve as chemical protectants. With this 6 year study in space, experimental data are provided to the discussion on the likelihood of ``Panspermia''.
Experiments are reviewed which were carried out on a number of balloon, rocket, and spacecraft missions and which have shown that inactivation of bare bacterial spores by solar ultraviolet radiation (UV) is, at most, a matter of a few minutes only. In addition, laboratory experiments have indicated that a temperature close to that of Space together with a protective coating by ice of simple molecules reduces sensitivity considerably. Extrapolation of these data to Space conditions allows the speculation that under these circumstances spores may survive for hundreds of thousands to millions of years; this time is sufficient for spores to travel from one solar system to another. Together with the enormous number of “protected” spores deposited from spacecrafts into Space these numbers allow for “modern panspermia” to work and point to a serious problem in “planetary quarantine”. In addition, they reveal constraints for panspermia in its classical sense. Here, however, UV irradiation may not be the limiting factor; but, HZE-particles of the cosmic galactic radiation may well be so.
This chapter presents an overview of those aspects of exobiology that can be investigated by experiments in earth orbit. The chapter focuses on the processes of organic chemical evolution in different bodies of solar system and beyond, and discusses the relevance of the organic compounds to the emergence of life on Earth. The possibility of interplanetary distribution of life is reviewed, and the experimental data testing this hypothesis is presented. In the chain of evolutionary steps towards the emergence of life, prebiotic chemical evolution is crucial. For the supply of organic molecules on the primitive earth, two plausible pathways are considered: terrestrial production of organics and import of extraterrestrial organic matter. In experiments simulating the putative conditions existing on the early earth, nearly all building blocks of life are synthesized, such as amino acids, purines, pyrimidines, and lipid-like compounds. However, in a non-reducing atmosphere, nitrogen containing compounds are unstable. Therefore, incoming extraterrestrial material may be considered as an essential source of organics on the primitive earth.
Onboard of several spacecrafts (Apollo 16, Spacelab 1, LDEF), spores of Bacillus subtilis were exposed to selected parameters of space, such as space vacuum, different spectral ranges of solar UV-radiation and cosmic rays, applied separately or in combination, and we have studied their survival and genetic changes after retrieval. The spores survive extended periods of time in space--up to several years--, if protected against the high influx of solar UV-radiation. Water desorption caused by the space vacuum leads to structural changes of the DNA; the consequences are an increased mutation frequency and altered photobiological properties of the spores. UV-effects, such as killing and mutagenesis, are augmented, if the spores are in space vacuum during irradiation. Vacuum-specific photoproducts which are different from the 'spore photoproduct' may cause the synergistic response of spores to the simultaneous action of UV and vacuum. The experiments provide an experimental test of certain steps of the panspermia hypothesis.
During the 19th and early 20th centuries, ideas related to the possible origin in space of bioorganic molecules, or seeds, or even germs and organisms (and how they reached the Earth) included the Panspermia theory. Based on the idea of the eternity of life proposed by eminent physicists - such as Arrhenius and Kelvin - 'Panspermia' is mainly divided into two branches: lithopanspermia (transport of germs inside stones traveling in space) and radiopanspermia (transport of spores by radiative pressure of stellar light). We point out some arguments to help to understand whether 'Panspermia' could exist nowadays as the same theory defined one century ago. And we wonder about the kind of evolution 'Panspermia' could have undergone during only a few decades. This possible evolution of the 'Panspermia' concept takes place in the framework of the emergence of a new field, Bioastronomy. We present how this discipline has emerged during a few decades and how it has evolved. We consider its relationship with the progression of other scientific fields, and finally we examine how it is now included in different projects of space agencies. Bioastronomy researches having become more and more robust during the last few years, we emphasize several questions about new ideas and their consequences for the current hypothesis of 'Panspermia' and of universal life.
The primary goal of exobiological research is to reach a better understanding of the processes leading to the origin, evolution and distribution of life on Earth or elsewhere in the universe. In this endeavour, scientists from a wide variety of disciplines are involved, such as astronomy, planetary research, organic chemistry, palaeontology and the various subdisciplines of biology including microbial ecology and molecular biology. Space technology plays an important part by offering the opportunity for exploring our solar system, for collecting extraterrestrial samples, and for utilizing the peculiar environment of space as a tool. Exobiological activities include comparison of the overall pattern of chemical evolution of potential precursors of life, in the interstellar medium, and on the planets and small bodies of our solar system; tracing the history of life on Earth back to its roots; deciphering the environments of the planets in our solar system and of their satellites, throughout their history, with regard to their habitability; searching for other planetary systems in our Galaxy and for signals of extraterrestrial civilizations; testing the impact of space environment on survivability of resistant life forms. This evolutionary approach towards understanding the phenomenon of life in the context of cosmic evolution may eventually contribute to a better understanding of the processes regulating the interactions of life with its environment on Earth.
On board of the NASA Long Duration Exposure Facility (LDEF), spores of Bacillus subtilis in monolayers (10(6)/sample) or multilayers (10(8)/sample) were exposed to the space environment for nearly six years and their survival was analyzed after retrieval. The response to space parameters, such as vacuum (10(-6) Pa), solar electromagnetic radiation up to the highly energetic vacuum-ultraviolet range (10(9) J/m2) and/or cosmic radiation (4.8 Gy), was studied and compared to the results of a simultaneously running ground control experiment. If shielded against solar ultraviolet (UV)-radiation, up to 80 % of spores in multilayers survive in space. Solar UV-radiation, being the most deleterious parameter of space, reduces survival by 4 orders of magnitude or more. However, up to 10(4) viable spores were still recovered, even in completely unprotected samples. Substances, such as glucose or buffer salts serve as chemical protectants. With this 6 year study in space, experimental data are provided to the discussion on the likelihood of "Panspermia".
Various mutagenic effects by heavy ions were studied in bacteria, irradiated at accelerators in Dubna, Prague, Berkeley or Darmstadt. Endpoints investigated are histidine reversion (B. subtilis, S. typhimurium), azide resistance (B. subtilis), mutation in the lactose operon (E. coli), SOS chromotest (E. coli) and lambda-prophage induction (E. coli). It was found that the cross sections of the different endpoints show a similar dependence on energy. For light ions (Z < or = 4) the cross section decreases with increasing energy. For ions of Z = 10, it is nearly independent of energy. For heavier ions (Z > or = 26) it increases with energy up to a maximum or saturation. The increment becomes steeper with increasing Z. This dependence on energy suggests a "mutagenic belt" inside the track that is restricted to an area where the density of departed energy is low enough not to kill the cell, but high enough to induce mutations.
The search for extraterrestrial intelligence (SETI) has been heavily influenced by solutions to the Drake Equation, which returns an integer value for the number of communicating civilisations resident in the Milky Way, and by the Fermi Paradox, glibly stated as: "If they are there, where are they?". Both rely on using average values of key parameters, such as the mean signal lifetime of a communicating civilisation. A more accurate answer must take into account the distribution of stellar, planetary and biological attributes in the galaxy, as well as the stochastic nature of evolution itself. This paper outlines a method of Monte Carlo realisation which does this, and hence allows an estimation of the distribution of key parameters in SETI, as well as allowing a quantification of their errors (and the level of ignorance therein). Furthermore, it provides a means for competing theories of life and intelligence to be compared quantitatively.
Es wird eine Folge aus vielen physikalisch und chemisch plausiblen Modellschritten betrachtet, die zur Selbstorganisation der Materie führt. Sie wird durch eine periodische Temperaturänderung und durch eine vielgestaltige räumliche Umgebung angetrieben, also durch eine Umgebungsstruktur, wie sie auf einem präbiotischen Planeten an manchen Stellen vorliegt. Ein solches spezielles Denkmodell zeigt den Rahmen im Prozeß der Selbstorganisation der Materie, zeigt, wo grundsätzliche Schwierigkeiten vorhanden und wie sie zu überwinden sind. Man findet, daß in dem Prozeß mehrere Barrieren überwunden werden müssen, die zum Teil durch Anhäufung von Kopierfehlern bedingt sind. Eine frühe Barriere wird dadurch überwunden, daß durch Aggregatbildung Kopierfehler ausgefiltert werden, eine andere dadurch, daß ein Apparat zur Synthese einer zellularen Hülle evolviert, die die Bauteile beisammenhält. Es entwickelt sich ein System, das eine primitive Replikase produziert, durch die ein rudimentärer Code stabilisiert wird. Eine spätere Barriere wird durch Unterteilung des Funktionssystems in getrennte Apparate für Replikation und Übersetzung der genetischen Information überwunden. – Mit dieser Betrachtung möchte man Experimente stimulieren und dazu anregen, diesen speziellen Denkansatz zu verwenden, um zu verbesserten und erweiterten Modellvorstellungen zu gelangen. Der Ansatz führt zu Aussagen über Vorbedingung, logisches Gerüst und Organisationsstruktur evolutiver Prozesse.
edited by his son, Francis Darwin. "In three volumes."
In the absence of extraneously added template, standard preparations of Q beta replicase spontaneously synthesize RNA in vitro, possibly as a result of RNA contamination. Using special enzyme purifications, Sumper and Luce presented evidence that self-replicating RNA not present ab initio can grow out of 'template-free' incorporation mixtures. In contrast to DNA polymerase I and RNA polymerase, which also show de novo synthesis, the products synthesized 'de novo' by Q beta replicase are RNA species containing nonrepetitive sequences of defined lengths which differ between experiments, even when synthesized under identical conditions, in fingerprints, chain lengths and kinetic parameters. Kinetic analysis of the de novo processes distinguished it from template-instructed synthesis and excluded an assumption of self-replicating RNA contamination. These conclusions were questioned recently by Hill and Blumenthal, who claimed to show that highly purified Q beta replicase preparations cannot produce RNA de novo. We now present evidence that, under the conditions required for de novo synthesis, Q beta replicase prepared according to their method is also capable of de novo synthesis. Furthermore, we show that Q beta replicase condenses nucleoside triphosphates to more or less random oligonucleotides.
In 1865/66 E. Haeckel for the first time suggested an evolutionary sequence in order to explain the origin of the first living cell. Haeckel's concept is compared with modern theories of the origin of life. It is evident that Haeckel has not as yet received the credit that he deserves for his evolutionary concept.
In contemporary cells biological information is largely stored in nucleic acids. Therefore, a prerequisite in many theories on the origin of cellular life is the pre-existence of self-replicating polynucleotides that had to be formed by abiotic processes on the prebiotic Earth. It is usually assumed that the spontaneous synthesis of a self-replicating polynucleotide could take place readily. However, serious stereochemical obstacles exist which make Such a synthesis extremely improbable. Amino acids on the other hand, which are abundantly formed in prebiotic simulation experiments, are relatively easily polymerized to macromolecules (protoproteins) that share with modern proteins many properties: e.g., definable non-random structure, selected amino acid sequences, enzyme-like activities and self-assembly into supramolecular structures. Prebiotic polyamino acids are therefore regarded by some scientists, including the present author, as the first informational macromolecules. The origin of this information is the chemical reactivity of the various prebiotic amino acids and their chemical response to their environment. The first informational polynucleotides were likely formed by a polynucleotide polymerase activity of prebiotic protoproteins. A contemporary model for this process is seen, e.g., in the activity of template-free Q beta-replicase.
Molecular Evolution and the Origin of Life
- S W Fox
- K Dose
S.W. Fox and K. Dose, Molecular Evolution and the Origin of Life, 2nd edition, Marcel Dekker, New York, 1977.