Abiogenesis

Early Earth & abiotic ‘axiom’: There are plenty of reasons to assume that abiotic generation of life is a reasonable assumption to make. First of all, is the clear trend in the fossil record of organisms going from simple to complex in our earliest to latest layers respectively[1]. Moreover is the organism predicted by the universal common ancestor hypothesis from evolution .Which depicts a single celled organism with an encapsulated genome and metabolic pathway, from comparison of the genes that all life shares. Moreover the planet is well suited for complex chemistry, with multiple environments where high concentrations of reactive molecules can enter in an liquid environment at temperatures suitable for synthesis, namely in geo-active areas on the Earth’s crust, which we know that from the accretion models, and from the known rate of radioactive decay of Uranium & Thorium within the Earth, that there was more internal heat within the Earth, which equates to a greater internal heat and hence greater geological activity The conditions of the early Earth and the length of time the Earth had to generate life is of great important to the feasibility of abiogenesis. Our oldest measurements of the Earth’s age from radiometric dating of our oldest zircon crystals (via Uranium-Lead dating) yields ages of ~4.3 billion years[2],which is pretty much in line with the ages found from our oldest asteroids (4500 Mya) [3].Our best scientific explanation for this is the formation of the solar system is from an accretion event, well studied computationally and is backed up by direct observations within the milky way [4]. RNA Synthesis: My arguments regarding the atmospheric composition at the time stand on the solar system accretion models, as well as analysis of the atmospheric composition of other planets within our own solar system. We find largely reduced environments on the coldest (and therefore best preserved) planets such as Pluto & Neptune, which have high concentrations of Hydrogen & Methane. Furthermore, given that Hydrogen is so abundant, any molecular oxygen present would have rapidly reacted with this hydrogen to produce water before the Earth had even finished accreting. Pro drops the points regarding the direct abiotic synthesis of RNA, what was interesting from the Urey-Miller experiments and other alike are the production of some of these reactive precursors, such as hydrogen cyanide and formamide in situ, therefore we know with great confidence that the ingredients I have listed before for RNA synthesis were likely present on the early Earth and were accessable by a number of pathways. It is true that the RNA world hypothesis is ‘unproven’, I never contended it was, but I do contend it is a very plausible hypothesis for the origin of life on Earth . Essentially every step towards autocatalysis, and therefore life has been performed experimentally [5]. There are multiple paths available within the RNA world hypothesis, and while it is is unlikely we will find the most likely one, just showing there are plausible pathways demonstrates abiogenesis is a likely hypothesis for the OOL. Encapsulation & UV Radiation: Pro is quite right in asserting there could be no O3 (Ozone) in a reducing atmosphere, which would increase the amount of UV Radiation reaching the Earth’s surface, however Pro gives no evidence that increased UV radiation would lead to much increased cleavage of RNA. Moreover, ironically, it may well be the case that the increased UV levels would actually drive the formation of nucleotides (!) [6]. One other important factor is encapsulation, which I did not get to discussing the in the last round. For encapsulation you need lipid-like molecules around on the early Earth. These were likely much more abundant than the RNA around at the time, as there are so many sources of these. For example, molecules found in meteorites, were found to self-assemble into vesicles (lipid capsules), and hydrothermal synthesis of lipid-type molecules is possible using carbon monoxide, carbon dioxide & water at high temperature/pressures such as those found at deep hydrothermal vents or geysers catalysed by various transition metals [7-10] The importance of encapsulation are several: 1. It solves any potential problem with UC radiation (as the vesicles absorb UV radiation) 2. It ‘traps’ inside long RNA chains (such as the ‘proto-genome’, or ribozymes) 3. It filters out large impurities and is permeable to small monomeric reactive molecules 4. It protects the RNA chain from degradation from other environmental factors My opponent asserts there is no evidence of self-replicating ribozymes, but this is demonstrably false, as this is exactly what has been reported numerous times in the literature, one example was just 196 nucleotides in length. Of course we have not addressed the search-space of all possible configurations of RNA that would be active in self-replication, but only a minor rate of activity is required to drive reproduction to self-sustaining levels [11-13]. What is most striking is we have already demonstrated that RNA oligomers of >120 bases have already been synthesised abiotically in water in the absence of any catalysis using just concentrated solutions of cGMP and cAMP. There are a number of other reports for shorter length oligomers also being formed [14-15] Conclusion: I have pretty much well-stated my case for the plausibility of abiogenesis, and the conditions that allow for the complex and rich chemistry involved in the process. Back to Con! References: 1. (http://news.illinois.edu...). 2. http://www.amnh.org... 3. http://elements.geoscienceworld.org... 4. http://www.dailygalaxy.com... 5. http://www.biologydirect.com... 6. http://arstechnica.com... 7. http://www.pnas.org... 8. http://www.ncbi.nlm.nih.gov... 9. http://www.ncbi.nlm.nih.gov... 10. http://www.ncbi.nlm.nih.gov... 11. http://www.pnas.org... 12. http://www.ncbi.nlm.nih.gov... 13. http://adsabs.harvard.edu... 14. http://pubs.rsc.org... 15. http://www.jbc.org...