Earth primeval conditions

The results so far available, and the models derived from them, indicate the following a reducing atmosphere is more favourable for amino acid synthesis. If, however, the partial pressure of methane on the primeval Earth was either zero or very low, a relatively high H2/CO or H2/CO2 ratio still allowed good rates of amino acid synthesis. It is, however, still an open question as to whether these concepts are realistic, because of the possibility that hydrogen could have escaped into space. It is arguable that in certain areas on the young Earth (and under unknown conditions),... 

Conditions on primeval Earth which led to eutectic freezing, and thus to concentration of the HCN solutions... 

About 40 different sugars are formed. Those required for nucleic acid synthesis, ribose and deoxyribose, are obtained in yields of less than 1%. It is completely unclear whether these could have been separated from the others under primeval Earth conditions (Shapiro, 1988). 

A ray of hope appeared when a synthetic route was developed in the laboratory of Albert Eschenmoser in Zurich, leading in good yields to ribose-2,4-diphosphate (in racemic form). The starting material was glycol aldehyde, which was phospho-rylated in the 2-position and then incubated with formaldehyde. Unfortunately the synthetic conditions are only those of a modern laboratory, but could the reaction have taken place on the primeval Earth (Muller et al., 1990). 

The synthesis of dipeptides under the conditions found on primeval Earth appears highly likely. The discovery that these small molecules can act as catalysts makes it possible to discuss their being involved in basic synthetic reactions occurring in an (as yet hypothetical) RNA world (Weber and Pizzarello, 2006). 

Earlier studies showed that reactions of sugars with ammonia lead to small molecules such as amines or organic acids. A. L. Weber has reported important autocatalytic processes occurring when trioses are allowed to react with ammonia under anaerobic conditions, such reactions provide products which are autocatalyt-ically active. Their autocatalytic activity was determined directly by investigating their effect on an identical triose-ammonia reaction. Both an increase in the triose degradation rate and an increased rate of synthesis of pyruvate, the dehydration product of the triose, were observed. Such processes may have been of importance for prebiotic chemistry occurring on the primeval Earth (Weber, 2007). 

This reaction is catalysed by traces of bases. Matthews remained true to HCN chemistry, which is indeed an attractive research area. HCN can polymerize under certain conditions the process can be induced by heat or radiation, both of which were certainly present the on primeval Earth. 

This interpretation of the experimental results is not accepted by Clifford Matthews, who has for many years defended the following hypothesis the prebiotic proteins (or peptides) are formed from HCN by polymerisation reactions and not from single a-amino acids (see Chap. 5). The necessary preconditions for polycondensation of amino acids—high temperatures, acidic conditions and the absence of water—were not present on primeval Earth. 

The amino acid, activated by uptake of SO3, reacts with a second molecule of amino acid to form the dipeptide, which can in turn react further to form a tripeptide (and so on). This peptide synthesis model, which is supported by experimental evidence, appeals because of its simplicity it may well correspond much more closely to conditions on the primeval Earth than do some other models (Chen and Yang, 2007). 

A combination of SIPS with the stabilising and synthesis-favouring properties of clay minerals was studied by Rode et al. (1999) in experiments involving dry/wet cycles. The simultaneous use of both SIPS and clay minerals as catalytically active surfaces led to peptides up to and including the hexamer (Gly)6. The question as to whether this technique fulfils prebiotic conditions can (within certain limitations) be answered positively, since periodic evaporation phases in limited areas (lagoons, ponds) are conceivable. The container material could have consisted of clay minerals. Further progress in the area of peptide synthesis under conditions which could have been present on the primeval Earth can be expected. 

The thermal synthesis of nucleoside-5 -phosphite monoester using (NH HPCb was carried out under relatively mild conditions (60°C, reaction time about 24 h) by A. W. Schwartz s group in Nijmegen, Holland in the case of uridine, the yield was 20%. Ammonium phosphate, however, cannot be used it gave yields of only 0.15% after very long reaction times (46 days). This confirms earlier suggestions that nucleoside-H-phosphonates, and condensation products possibly derived from them, would have been formed more readily on the primeval Earth than nucleotides (de Graaf and Schwartz, 2005). 

However, the question must always be asked as to whether these processes could have taken place on the primordial Earth in its archaic state. The answer requires considerable fundamental consideration. Strictly speaking, most of the experiments carried out on prebiotic chemistry cannot be carried out under prebiotic conditions , since we do not know exactly what these were. In spite of the large amount of work done, physical parameters such as temperature, composition and pressure of the primeval atmosphere, extent and results of asteroid impacts, the nature of the Earth s surface, the state of the primeval ocean etc. have not so far been established or even extrapolated. It is not even sure that this will be possible in the future. In spite of these difficulties, attempts are being made to define and study the synthetic possibilities, on the basis of the assumed scenario on the primeval Earth. Thus, for example, in the case of the SPREAD process, we can assume that the surface at which the reactions occur could not have been an SH-containing thiosepharose, but a mineral structure of similar activity which could have carried out the necessary functions just as well. The separation of the copy of the matrix could have been driven by a periodic temperature change (e.g., diurnal variation). For his models, H. Kuhn has assumed that similar periodic processes are the driving force for some prebiotic reactions (see Sect. 8.3). 

The difficulties of implementing glycosidic bonds between the nucleotides under the conditions present on the primeval Earth The inability to achieve double-sided, non-enzymatic matrix polymerisation... 

In the same year, Miller and the biologist Antonio Lazcano (National Autonomous University of Mexico) spoke out against hypotheses that life could have originated at hydrothermal vents. They believe that the presence of thermophilic bacteria (the oldest life forms) does not prove that biogenesis occurred in the depths of the oceans. Stanley Miller sees a greater chance for successful pre-biotic chemistry under the conditions of a cold primeval Earth rather than at high temperatures in hydrothermal regions (Miller and Lazcano, 1995). 

A detailed theoretical study of the properties of the redox system FeS/FeS2 was carried out in the Department of Geosciences of SUNY Stony Brook (Schoonen et al., 1999). The authors conclude that the hypothetical reduction of CO2 (by the FeS/FeS2 redox pair) formulated in Wachtershauser s early work, and the carbon fixation cycle on the primeval Earth associated with it, probably could not have occurred. This judgement is made on the basis of a theoretical analysis of thermodynamic data other conditions would naturally have been involved if CO had reacted rather than C02. It is not known whether free CO existed in the hydrosphere, or if so, at what concentrations. 

How could this problem be solved Only traces of thioesters are formed from free carboxylic acid and thiols in aqueous solution, i.e., the equilibrium reaction 7.15 is shifted to the left. According to de Duve (1991), there are two possibilities for spontaneous thioester synthesis under conditions present on the primeval Earth ... 

Woese chose the name archaebacteria because these microorganisms grow best under conditions which were probably found on the primeval Earth between 3.5 and 4 billion years ago hot boiling water and thermal vents, highly acidic environment, oxygen-free atmosphere and high salt concentrations. 

The decision to write a book on the origin (or origins) of life presupposes a fascination with this great problem of science although my first involvement with the subject took place more than 30 years ago, the fascination is still there. Experimental work on protein model substances under simulated conditions, which may perhaps have been present on the primeval Earth, led to one of the first books in German on Chemical and Molecular Evolution Klaus Dose (Mainz) had the idea of writing the book and was my co-author. 

It is interesting that, when organic and inorganic tripolyphosphates were employed under the same conditions, only 0.2-0.6 % of the phosphate donor was utilized (Lowenstein, 1958, 1960 Tetas and Lowenstein, 1963 Le Port et al., 1971). Our experimental findings thus lead to the conclusion that, as the Earth cooled and a hydrosphere was formed on its surface, a variety of transphosphorylation reactions became possible in the primeval ocean, in particular, the phosphorylation of Pi by PolyP to give pyrophosphate. It should be noted that the non-enzymatic synthesis of PolyP and pyrophosphate on the primitive Earth could take place not only in solutions, but also on the surface of some minerals with anion-exchange properties (Arrhenius et al., 1993,1997). 

Whilst the potential for synthesis of cyclopropene under volcanic conditions on primeval earth is recognized , the extent to which the ring system occurs in nature is known for only four classes of compounds, one of which involves cyclopropenone derivatives. Plants of the order Malvales contain varying amounts of the biologically active and homologous cyclopropene fatty acids sterculic acid (2) and malvalic acid (3). The... 

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