Environments primitive Earth

Once chirality is induced and amplified by some mechanism, the excess must first persist and then propagate in order to survive. A distinctive characteristic of homo-chiral protein and nucleic acid biopolymers is that they function within the enclosed environment of cells, which provide a membranous boundary structure that separates the intracellular components from the external environment. It has accordingly been postulated frequently that analogous but simpler enclosed environments must have been available and operative on the primitive Earth. 

The question as to the potential availability of the requisite amphiphilic precursors in the prebiotic environment has been addressed experimentally by Deamer and coworkers, [143,145] who looked into the uncontaminated Murchison chondrite for the presence of such amphiphilic constituents. Samples of the meteorite were extracted with chloroform-methanol and the extracts were fractionated by thin-layer chromatography, with the finding that some of the fractions afforded components that formed monomolecular films at air-water interfaces, and that were also able to self-assemble into membranous vesicles able to encapsulate polar solutes. These observations dearly demonstrated that amphiphiles plausibly available on the primitive Earth by meteoritic infall have the ability to self-assemble into the membranous vesides of minimum protocells. ... 

This unexpected consequence of the efficient reaction of carbon dioxide can be expressed in an other way NCAs can be considered as the most activated amino acid species achievable in water in the environment of the primitive Earth. The only exception would be species bearing a chemical protection of the a-amino groups that are unlikely because peptide elongation would have been complicated by the necessity of an additional deprotection step. From a prebiotic perspective, there is consequently no need to search for activated amino acid derivatives with a degree of activation higher than NCAs (thermodynamic limit in Fig. 3). 

Although the discovery of amino acid formation was of tremendous significance in establishing that the raw materials of proteins were easy to obtain in a primitive Earth environment, there remained a larger question as to the nature of the origin of genetic materials—in particular the origin of DNA and RNA molecules. 

A more complex system is favored by those who propose that the first life must be able to generate the compounds essential for life (metabolism) and this life is protected from the environment inside a container , a structure similar to a cell membrane, so the integrity of the life can be protected from a changing environment. The spontaneous formation of a metabolic system appears to have been too complicated to occur on the primitive Earth, so we favor the life on the rocks scenario. 

All of these results demonstrate that 7k-REC is highly functional both in vivo and in vitro. Archaea in general, and hyperthermophilic archaea in particular, are thought to evolve from and still live in environments very similar to that of primitive earth. Cells at that time might have been exposed to harsh conditions including fairly strong UV light. Under this stress it would be essential to maintain effective DNA repair systems. 

It is now well known that this chemical theory on the origin of life was first published more than 50 years ago by A. I. Oparin. The essence of this theory is based not on the spontaneous generation of life proposed by earlier authors, but on the progressive chemical evolution and self-organization of organic matter on a reducing, or non-oxidizing, primitive earth environment. 

The point of merit is that it was required that POP linkages come from some source before life could propagate on Earth. Once life was functional, polyphosphates are a byproduct of life, but before there was life some chemical source was required. Several demonstration models have been proposed, but there are many more possible ways that small quantities could have been available at isolated spots on primitive Earth. It is reasonably certain that condensed phosphates were not generally distributed and that they had a relatively short life in any environments where life could exist. °... 

The steady state concentrations of HCN would have depended on the pH and temperature of the early oceans and the input rate of HCN from atmospheric synthesis. Assuming favorable production rates, Miyakawa et al (30) estimated steady state concentrations of HCN of 2 x 10 M at pH 8 and 0°C in the primitive oceans. At 100° C and pH 8 the steady state concentration was estimated as 7 x 10 M. HCN hydrolyzes to formamide which then hydrolyzes to formic acid and ammonia. It has been estimated that oligomerization and hydrolysis compete at approximately 10 M concentrations of HCN at pH 9 (31), although it has been shown that adenine is still produced from solutions as dilute as 10 M (32). If the concentration of HCN were as low as estimated, it is possible that HCN tetramer formation may have occurred on the primitive Earth in eutectic solutions of HCN-H2O, which may have existed in the polar regions of an Earth of the present average temperature. High yields of the HCN tetramer have been reported by cooling dilute cyanide solutions to temperatures between -10° C and -30° C for a few months (31). Production of adenine by HCN polymerization is accelerated by the presence of formaldehyde and other aldehydes, which could have also been available in the prebiotic environment (29). 

In the 1950s it was assumed that the primitive Earth atmosphere consisted of methane CH4, ammonia NH3, hydrogen H2 and water H2O and S.L. Miller and H.C. Urey carried out a famous experiment at the University of Chicago. They simulated the primitive Earth atmosphere and ran continuous electric currents simulating lightning storms, which were very common on the early Earth, to this environment. After one week, 10-15 amino acids were found in this primordial soup. 

The authors suggest that it was the structural diversity of the environment which made biogenesis possible in other words, there was an enormous selection of regions with different properties and states on the young Earth which acted as stimuli for the increasing complexity of the evolving systems. As complexity increased, those regions of the primeval Earth which were not available for earlier, more primitive systems could be colonized . 

In addition to the transition phenomena mentioned so far in the present section, a variety of even larger scale processes might have operated during chemical evolution, namely, instabilities and bifurcations in the very atmospheric environment within which life emerged. As shown in the paper by Marcel Nicolet, the earth s atmosphere is the theater of a variety of complex chemical and transport phenomena. Moreover, as explained by Stanley L. Miller, the composition of the primordial atmosphere has certainly affected deeply the chemistry in the primitive oceans. Conversely, once life emerged the properties of the atmosphere changed radically, and this must have affected the further course of evolution. We refer to Prather et al.41 and North et al.42 for an account of present views on large scale transitions in the earth-atmosphere system. 

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