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The Emergence of Life on Prebiotic Earth: The Origin of Life, Self Replicating Metabolic Pathways & The RNA World

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Introduction

The Emergence of Life on Prebiotic Earth: The Origin of Life, Self Replicating Metabolic Pathways & The RNA World With even just a single cell as a starting point, Darwinian evolution offers an elegant and powerful algorithm for bringing about the vast diversity, and ranging complexity of the living world. It is not difficult to imagine how, by acting on ?surplus populations? of replicating organisms; evolutionary forces such as natural selection would eventually lead to adaptations, niches and diversification. However, as true Darwinian evolution requires genetic replication, with heredity information being passed on to ?progeny? in order to enact its divergent processes; it is powerless to account for the emergence of the first life (Darwin, 1859). The first serious scientific research into how life emerged from the prebiotic environment of the early Earth began in 1953; with the now famous Miller-Urey prebiotic or ?primordial? soup experiments, at the University of Chicago. In these experiments, Miller passed sparks, as a substitute for lighting, through a gaseous mix of ammonia, hydrogen, methane and water, which were believed at the time to be the major constituents of the early earth?s atmosphere. The results of the experiments predicted that over time, the young oceans would have become a rich soup of organic monomers such as amino acids, laying the foundations for abiogenesis (Miller and Schlesinge, 1983). ...read more.

Middle

However the discovery of micro-compartments, formed in aggregates deposited at alkali hydrothermal vents, revived the theory; as they provided an environment which overcome the problem of reaction products diffusing into the ocean. These micro-compartments also helped solve a problem faced by both the soup and RNA world theories. Namely, how a disorganised solution of organic chemical components could ever make the transition to a self-contained, co-ordinated chemical system, capable of concentrating reaction products and other vital molecules within its self. (Dawkins, 1986) (Lane, 2010). Along with solving the problems of ‘compartment & concentration’ the alkali vent environment has become the central focus of present day research into biopoiesis. The hydrothermal reactor hypothesis, built around the vents, proposes a ‘metabolism first’ approach, involving much smaller molecules at much higher concentrations. The hydrothermal reactor hypothesis is not intended to be an alternative to RNA based life, but instead shows how geology at the vents could have provided the structure and conditions which led to free living RNA and eventually DNA based cells (McKay, 2004) Primarily developed by William Martin from the institute of botany at the University of Düsseldorf, and Michael Russell from the Scottish Universities Environmental Research Centre; the alkali vent reactor hypothesis offer’s a thermodynamically favourable solution to the problem of how complex organic molecules, such as RNA could be arrived at. ...read more.

Conclusion

(Russell and Martin, 2004) The field of origins research is still in its infancy, and both the vent reactor, and RNA world theory are far from conclusive. The best evidence comes not from the vent environment its self, but from corroborating researcher?s findings with evidence from the fields of evolutionary biology and biochemistry. Many of the metabolic pathways used by present day organisms are believed to be very ancient, diverging only slightly between different taxonomic classes. What has emerged from abiogenesis research is reliable and reproducible evidence, which shows that these metabolic pathways are strongly self organising in a range of environments, including that of the vents. Furthermore, the products of these simple reactions have been shown to ?piggy back? there way upward to increasing levels of complexity. A paper, published in the journal chemistry in August 2005, showed that iron sulphide and amino acids were capable of catalysing the formation of other small organic molecules, such as nucleic acids. These original reaction products began to catalyze new reactions, eventually setting-up feedback loops, and developing into metabolic networks which gradually increased in complexity. While this does not conclusively prove that life emerged at the vents, it shows that issues, such as RNA synthesis are overcome by the energy rich and selectively concentrative micro compartments. In which organic ?precursor? compounds arise almost immediately, leading to formation of complete nucleotides. ...read more.

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