Creating several amino acids is easy. The hard part is coercing the amino acids to link
together in a chain to form a protein. RNA proves much more difficult because even the
building blocks are hard to synthesize. Furthermore, once they are created, they do not
last long. This makes it difficult to understand how the necessary building blocks
achieved a suitable concentration for further reactions and seriously brings into
question the current RNA world hypothesis and other origin of life theories that depend on it.
Several key building blocks will now be considered.
Adenine and Cytosine
Adenine has been synthesized in the lab from concentrated solutions of hydrogen cyanide
and ammonia. While this process works in the lab, it is not clear how the necessary
conditions to create adenine would arise in nature.
To synthesize significant quantities of adenine, a concentrated solution of
hydrogen cyanide and ammonia is required. Concentrating hydrogen cyanide and ammonia under
plausible conditions is problematic. Hydrogen cyanide is a very reactive chemical. In low
concentrations, it reacts with water to form many products that are not adenine. These
side reactions use up the hydrogen cyanide and lower its concentration. To make the
process more difficult, one of the most abundant chemicals produced in the early
atmosphere was undoubtably formaldehyde and “Formaldehyde reacts spontaneously with
hydrogen cyanide to form cyanohydrin, a well known reaction that has vexed workers in the
field of prebiotic chemistry relying on the unencumbered availability of HCN in high
concentration to form a plethora of evolved molecules.”21Ammonia is
equally problematic because it decays rapidly when exposed to sunlight,15 and
it boils at sub-freezing temperatures. So while some adenine might be formed under
plausible conditions, very little is produced. The high concentration of ammonia and
hydrogen cyanide required to make adenine does not represent plausible prebiotic
conditions.3
Because adenine has been found in meteorites, there is evidence that it is
produced by nature in space.3 Nevertheless, based on the above discussion,
adenine was certainly a very rare chemical 4 billion years ago.
Cytosine is much more problematic than adenine. It has never been produced
under any plausible prebiotic conditions, even in minute quantities. It is not found in
meteorites, so it is not easily synthesized in space. Cytosine is not stable in water. Its
lifetime depends on the temperature. At 100 degrees Celsius, cytosine decomposes in 19
days. At room temperature, the decomposition is 340 years. These observations have led
Miller and several other researchers to suggest that Cytosine was not found in the first
self replicating molecule. 5,6
Next: Prebiotic Synthesis of Ribose
Previous: RNA Prebiotic Synthesis
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