RNa world
A key idea which could explain the origin of life is the idea that, before there were any complex cells, there was simply a world containing self-replicating RNA. This idea was triggered by the discovery that it was thermodynamically feasible for RNA to replicate spontaneously. In this model, as the RNA continued to replicate, the parts which carried the information crucial to life would become more prevalent. This means that this theory would represent a very early version of evolution by Darwinian selection.
However, there are problems facing this hypothesis. It would require the initial assumed presence of the basic nucleotides of RNA: Adenine, Guanine, Cytosine and Uracil. In particular, scientists have yet to come up with an abiotic method of synthesizing Cytosine and Uracil.
Furthermore, although it is a thermodynamically plausible reaction, many other factors could influence it. For example, it depends heavily on the primordial soup theory which states that there were free nucleotides, suspended in a solution in which they could react.
A further hypothesis is that, preceding this RNA world, there was a world which contained only a completely different type of nucleic acid, perhaps TNA, PNA, GNA or another type, which may still be undiscovered. This is based on research which suggests that in an
extracellular environment Ribose sugars are prone to hydrolysis, and are therefore too unstable. Although these hypotheses have yet to be disproven, the evidence substantiating them is currently not much more than circumstantial and speculative.
However, there are problems facing this hypothesis. It would require the initial assumed presence of the basic nucleotides of RNA: Adenine, Guanine, Cytosine and Uracil. In particular, scientists have yet to come up with an abiotic method of synthesizing Cytosine and Uracil.
Furthermore, although it is a thermodynamically plausible reaction, many other factors could influence it. For example, it depends heavily on the primordial soup theory which states that there were free nucleotides, suspended in a solution in which they could react.
A further hypothesis is that, preceding this RNA world, there was a world which contained only a completely different type of nucleic acid, perhaps TNA, PNA, GNA or another type, which may still be undiscovered. This is based on research which suggests that in an
extracellular environment Ribose sugars are prone to hydrolysis, and are therefore too unstable. Although these hypotheses have yet to be disproven, the evidence substantiating them is currently not much more than circumstantial and speculative.
Primordial Soup
The early earth had a reducing atmosphere, containing high quantities of hydrogen, which when exposed to energy formed simple organic monomers such as nucleotides. In some locations e.g. shorelines these monomers were in higher concentrations forming a 'soup' allowing the formation of more complex molecules.
In 1953 Miller and Urey performed an experiment to discover whether or not life can come from these 'chemical odds and ends'. They reacted a mixture of methane, hydrogen, ammonia and water in a spark discharge (energy) to spontaneously form amino acids and small organic molecules.
In 1953 Miller and Urey performed an experiment to discover whether or not life can come from these 'chemical odds and ends'. They reacted a mixture of methane, hydrogen, ammonia and water in a spark discharge (energy) to spontaneously form amino acids and small organic molecules.
For more information on the RNA world visit; http://exploringorigins.org/rnaworld.html