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PubMed1979

The Martian atmosphere: some unanswered questions.

The study of the Martian atmosphere and its significance for the possible origin of life on Mars is still very incomplete. Further investigations are needed to define the total volatile inventory, the early history of the atmosphere, and the relationship of the atmosphere to the question of indigenous life. In addition, studies of Venus, comets, and the Jupiter system will add significantly to our abilities to understand the early history of Mars.

Carbon↗

PubMed1985

Soluble minerals in chemical evolution. I. Adsorption of 5'-AMP on CaSO4--a model system.

The adsorption of 5'-AMP onto solid CaSO4 2H2O was studied in a saturated suspension as a function of pH and electrolyte concentration. The adsorption is pH-dependent and is directly correlated with the charge on the 5'-AMP molecule which is determined by the state of protonation of the N-1 nitrogen of the purine ring and the phosphate oxygens. It is proposed that the binding occurs between the nucleotide and the salt is electrostatic in nature. The adsorption decreases with increasing ionic strength of the solution which means that in a fluctuating environment of wetting and drying cycles, a biomolecule similar to 5'-AMP could be expected to desorb during the drying phase. The results indicate that CaSO4 2H2O can serve as a concentrating surface for biomolecules. The significance of this is discussed with regard to the possible role of soluble minerals and their surfaces in a geochemical model consistent with the evolution of the Earth and the origin of life.

Adenosine Monophosphate↗

PubMed1992

Comet Halley as an aggregate of interstellar dust and further evidence for the photochemical formation of organics in the interstellar medium.

Photolysis of mixtures of CO:NH3:H2O at 12 K results in the formation of an organic residue which is not volatile in high vacuum at room temperature. Analysis of this fraction by GC-MS resulted in the detection of C2-C3 hydroxy acids and hydroxy amides, glycerol, urea, glycine, hexamethylene tetramine, formamidine and ethanolamine. Use of isotopically labeled gases made it possible to establish that the observed products were not contaminants. The reaction pathways for the formation of these products were determined from the position of the isotopic labels in the mass spectral fragments. The significance of these findings to the composition of comets and the origins of life is discussed.

Dust↗

PubMed2003

Testing fundamental evolutionary hypotheses.

Sober and Steel (J. Theor. Biol. 218, 395-408) give important limits on the use of current models with sequence data for studying ancient aspects of evolution; but they go too far in suggesting that several fundamental aspects of evolutionary theory cannot be tested in a normal scientific manner. To the contrary, we show examples of how some alternatives to the theory of descent can be formulated in such a way that they lead to predictions that can be evaluated (and rejected). The critical factor is a logical formulation of the alternatives, even though not all possible alternatives can be tested simultaneously. Similarly, some of the limits using DNA sequence data can be overcome by other types of sequence derived characters. The uniqueness (or not) of the origin of life, though still difficult, is similarly amenable to the testing of alternative hypotheses.

Animals↗

PubMed1999

On the origin of metabolic pathways.

The heterotrophic theory of the origin of life is the only proposal available with experimental support. This comes from the ease of prebiotic synthesis under strongly reducing conditions. The prebiotic synthesis of organic compounds by reduction of CO(2) to monomers used by the first organisms would also be considered an heterotrophic origin. Autotrophy means that the first organisms biosynthesized their cell constituents as well as assembling them. Prebiotic synthetic pathways are all different from the biosynthetic pathways of the last common ancestor (LCA). The steps leading to the origin of the metabolic pathways are closer to prebiotic chemistry than to those in the LCA. There may have been different biosynthetic routes between the prebiotic and the LCAs that played an early role in metabolism but have disappeared from extant organisms. The semienzymatic theory of the origin of metabolism proposed here is similar to the Horowitz hypothesis but includes the use of compounds leaking from preexisting pathways as well as prebiotic compounds from the environment.

Amino Acids↗

PubMed2006

Historical contingency and the purported uniqueness of evolutionary innovations.

Many events in the history of life are thought to be singular, that is, without parallels, analogs, or homologs in time and space. These claims imply that history is profoundly contingent in that independent origins of life in the universe will spawn radically different histories. If, however, most innovations arose more than once on Earth, histories would be predictable and replicable at the scale of functional roles and directions of adaptive change. Times of origin of 23 purportedly unique evolutionary innovations are significantly more ancient than the times of first instantiation of 55 innovations that evolved more than once, implying that the early phases of life's history were less replicable than later phases or that the appearance of singularity results from information loss through time. Indirect support for information loss comes from the distribution of sizes of clades in which the same minor, geologically recent innovation has arisen multiple times. For three repeated molluscan innovations, 28-71% of instantiations are represented by clades of five or fewer species. Such small clades would be undetectable in the early history of life. Purportedly unique innovations either arose from the union and integration of previously independent components or belong to classes of functionally similar innovations. Claims of singularity are therefore not well supported by the available evidence. Details of initial conditions, evolutionary pathways, phenotypes, and timing are contingent, but important ecological, functional, and directional aspects of the history of life are replicable and predictable.

Animals↗

PubMed1976

Scavenging of soluble organic matter from the prebiotic oceans.

The existence of hot or cold "nutrient broth" or "primeval soup" is challenged on the basis of the recent geochemistry of soluble organic carbon in the oceans. Most of the dissolved organic carbon is recycled quickly by organisms, but the residual, biologically refractive, organic matter is efficiently scavenged from the oceans (residence time of 1000 to 3500 years) by nonbiologically mediated chemical and physical processes, such as adsorption on sinking minerals, polymerization and aggregation to humic type polymers or by aggregation to particulate matter through bubbling and sinking of this material to the ocean bottom. Since there is no reason to believe that such nonbiological scavenging was not operative in the prebiotic oceans as well, then the prolonged existence of "organic soup" is very doubtful. The question of the origin of life is thus assumed to be related to solid-liquid interfacial activity, and the answer may be associated with sediment-water interaction rather than with solution chemistry.

Carbon↗

PubMed1978

Biotin. Its place in evolution.

In the previous article we try to give an explanation for the success of models of enzymatic reactions in which coenzymes play a role. However, one vital cofactor that has thus far not yielded appreciably to this approach is biotin. We attempt to show that biotin presents a fundamentally new sort of problem to bioorganic chemistry; this problem requires consideration both of the origin of life and subsequent evolution in any attempt to understand the anomalies offered by this cofactor.

Acetyl-CoA Carboxylase↗

PubMed1986

Exobiology and future Mars missions: the search for Mars' earliest biosphere.

The primordial Mars may have possessed a thick carbon dioxide atmosphere, with liquid water common on the surface, similar in many ways to the primordial Earth. During this epoch, billions of years ago, the surface of Mars could have been conducive to the origin of life. It is possible that life evolved on Mars to be later eliminated as the atmospheric pressure dropped. Analysis of the surface of Mars for the traces of this early martian biota could provide many insights into the phenomenon of life and its coupling to planetary evolution.

Aluminum Silicates↗

PubMed2003

Antithrombotic properties of a direct thrombin inhibitor with a prolonged half-life and AT-mediated factor Xa inhibitory activity.

Rebound thrombin generation after successful thrombolysis might be related to (i) too short-term anticoagulant therapy and to (ii) the inability of heparin derivatives to inhibit clot-bound thrombin. To meet these shortcomings, a compound was synthesized, which consists of a pentasaccharide conjugated to a direct thrombin inhibitor. This compound (Org 42675) has a 10 times longer half-life compared with the original half-life of the direct thrombin inhibitor, while the thrombin inhibitory activity is maintained. An extra advantage of this product is the inhibitory activity on thrombin generation via antithrombin III (AT)-mediated factor (F)Xa inhibition. Org 42675 inhibited in vitro clot-bound thrombin with similar activity to the direct thrombin inhibitor argatroban. In experimental models in rats, Org 42675 showed on a molar base similar antithrombotic activity to unfractionated heparin, was more active than argatroban and was more active than fondaparinux sodium (AT-mediated FXa inhibitor) in arterial thrombosis. Finally, Org 42675 was far more active than the three reference compounds in an experimental thrombolysis model in rabbits. These properties of Org 42675, with its FXa and (clot-bound) thrombin inhibitory activity in combination with its long half-life, make this compound a powerful drug that is likely to be effective in the prevention of re-occlusion after successful thrombolysis in man.

Animals↗

PubMed2004

Introns: mighty elements from the RNA world.

The discovery of RNA-based enzymatic activity by Thomas Cech's and Sidney Altman's laboratories was a momentous event that led Walter Gilbert to the concept of an "RNA world"--a primitive ancient stage of life that existed before the appearance of DNA and protein molecules. A year later, Gilbert formulated "the exon theory of genes," which hypothesized that introns are very ancient genetic elements present at the earliest stages of life in the RNA world. This theory has been fiercely debated and still has vigorous supporters and opponents. In this communication, we explore peculiarities in the RNA-protein world and their effect on intron-exon structures. We demonstrate that these peculiarities, which exist in the absence of DNA, could shed light on introns' original functions as well as the important role they might have played in the origin of life. For ancient DNA-lacking cells, a crucial problem existed in distinguishing two distinct subsets of RNAs: those messenger molecules coding for proteins and those heritable genetic molecules complementary to messenger RNAs that propagate the genetic information through generations. We propose that ancient introns could act as markers of RNA subsets, directing them to different functions.

Animals↗

PubMed1968

Ammonium ion concentration in the primitive ocean.

If ion exchange on clay minerals regulated the cationts in the primitive ocean as it does in the present ocean, the pH would have been 8 and the K(+) concentration 0.01M. Since NH(4)(+) and K(+) are similar in their claymineral equilibria, the maximum NH(4) (+) concentration in the primitive ocean would also have been 0.01M. An estimate of the minimum NH(4)(+) concentratin is 1 x 10(-3)M, based on the reversible deamination of aspartic acid and the assumption that aspartic acid is necessary for the origin of life. The rate of this nonenzymic deamnination is rapid on the geological time scale.

Ammonia↗

PubMed2003

A case for the extreme antiquity of recombination.

Recombination is usually assumed to be a mode of reproduction that evolved long after asexual reproduction in response to specific genetic and environmental circumstances. Here the argument is made that recombination was an evolutionary development as ancient as the origins of life. To support this proposition four lines of evidence are given, in particular, the need for primordial genomes to acquire substantial length and to escape from Muller's Ratchet.

Genome↗

PubMed1987

The triose model: glyceraldehyde as a source of energy and monomers for prebiotic condensation reactions.

Glyceraldehyde acts as a source of energy and monomers in a new model of the origin of life. The simplest form of the model functions by converting formaldehyde from the environment into glyceraldehyde which spontaneously forms hemiacetal adducts that are oxidized to polyglyceric acid. Polyglyceric acid, in turn, acts as an autocatalyst with a rudimentary replicating ability. A unique property of the model is its ability to unite the origin of metabolism and the origin of polymer synthesis into a single process. Furthermore, the chemical resemblance of the model to glycolysis gives it the potential to develop a biological metabolism in a straightforward manner.

Calorimetry↗

PubMed1989

Pre-biotic organic matter from comets and asteroids.

Several authors have suggested that comets or carbonaceous asteroids contributed large amounts of organic matter to the primitive Earth, and thus possibly played a vital role in the origin of life. But organic matter cannot survive the extremely high temperatures (>10(4) K) reached on impact, which atomize the projectile and break all chemical bonds. Only fragments small enough to be gently decelerated by the atmosphere--principally meteors of 10(-12)-10(-6) g--can deliver their organic matter intact. The amount of such 'soft-landed' organic carbon can be estimated from data for the infall rate of meteoritic matter. At present rates, only approximately 0.006 g cm-2 intact organic carbon would accumulate in 10(8) yr, but at the higher rates of approximately 4 x 10(9) yr ago, about 20 g cm-2 may have accumulated in the few hundred million years between the last cataclysmic impact and the beginning of life. It may have included some biologically important compounds that did not form by abiotic synthesis on Earth.

Atmosphere↗

PubMed2005

A hydrogen-rich early Earth atmosphere.

We show that the escape of hydrogen from early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on early Earth would have been a more favorable place for the origin of life than previously thought.

Amino Acids↗

PubMed1997

Detection of organic matter in interstellar grains.

Star formation and the subsequent evolution of planetary systems occurs in dense molecular clouds, which are comprised, in part, of interstellar dust grains gathered from the diffuse interstellar medium (DISM). Radio observations of the interstellar medium reveal the presence of organic molecules in the gas phase and infrared observational studies provide details concerning the solid-state features in dust grains. In particular, a series of absorption bands have been observed near 3.4 microns (approximately 2940 cm-1) towards bright infrared objects which are seen through large column densities of interstellar dust. Comparisons of organic residues, produced under a variety of laboratory conditions, to the diffuse interstellar medium observations have shown that aliphatic hydrocarbon grains are responsible for the spectral absorption features observed near 3.4 microns (approximately 2940 cm-1). These hydrocarbons appear to carry the -CH2- and -CH3 functional groups in the abundance ratio CH2/CH3 approximately 2.5, and the amount of carbon tied up in this component is greater than 4% of the cosmic carbon available. On a galactic scale, the strength of the 3.4 microns band does not scale linearly with visual extinction, but instead increases more rapidly for objects near the Galactic Center. A similar trend is noted in the strength of the Si-O absorption band near 9.7 microns. The similar behavior of the C-H and Si-O stretching bands suggests that these two components may be coupled, perhaps in the form of grains with silicate cores and refractory organic mantles. The ubiquity of the hydrocarbon features seen in the near infrared near 3.4 microns throughout out Galaxy and in other galaxies demonstrates the widespread availability of such material for incorporation into the many newly forming planetary systems. The similarity of the 3.4 microns features in any organic material with aliphatic hydrocarbons underscores the need for complete astronomical observational coverage in the 2-30 microns region, of lines of sight which sample dust in both dense and diffuse interstellar clouds, in order to uniquely specify the composition of interstellar organics. This paper reviews the information available from ground-based observations, although currently the Infrared Satellite Observatory is adding to our body of knowledge on this subject by providing more extensive wavelength coverage. The Murchison carbonaceous meteorite has also been used as an analog to the interstellar observations and has revealed a striking similarity between the light hydrocarbons in the meteorite and the ISM; therefore this review includes comparisons with the meteoritic analog as well as with relevant laboratory residues. Fundamental to the evolution of the biogenic molecules, to the process of planetary system formation, and perhaps to the origin of life, is the connection between the organic material found in the interstellar medium and that incorporated in the most primitive solar system bodies.

Astronomy↗

PubMed1993

[A mathematical model for the dynamics of primitive biological macromolecules and its evolutionary implications].

A mathematical model, adopted from the logistic equations for population growth and interspecific competition in ecology, was proposed for the dynamics of primitive biological macromolecules: [formula: see text] where Nm is the copy number of a kind of biological macromolecule in primitive environment at time t. rm is the intrinsic replicating capacity (rate) of the macromolecule. Km is the carrying capacity (resource limit) of the primitive environment. dNm/dt is the instantaneous rate of increase of copy number of the primitive biological macromolecule beta 12 and beta 21 are competition coefficients concerning the inhibition of macromolecule 2 on macromolecule 1 (beta 12), and macromolecule 1 on macromolecule 2 (beta 21) other lower indexes in the equations refer to macromolecule 1 or 2. By analysing the possible competition outcomes deduced from the model, a conclusion with evolutionary implications could be drawn that the biological diversity would be very low shortly after the origin of life in the primitive biosphere. In other words, the abundant biological macromolecules capable of replicating in the primitive biosphere would be quite unique in kinds, and this uniqueness would therefore be the initial basis of biological evolution which would then go from low biological diversity to high biological diversity. The model is also helpful for the understanding of the origin of repeated sequences which are widely present in the genomes of modern organisms.

Animals↗