Crick and Orgel and molybdenum...

Crick and Orgel proposed their Directed Panspermia theory at a conference on Communication with Extraterrestrial Intelligence, organized by Carl Sagan and held at the Byuraka Observatory in Soviet Armenia in 1971. This theory which they described as an “highly unorthodox proposal” and “bold speculation” was presented as a plausible scientific hypothesis. Two years after the conference they published an article in Icarus on 1973.

Crick and Orgel were careful to point out that Directed Panspermia was not a certainty; but rather a plausible alternative that ought to be taken seriously. In thepaper Crick and Orgel recognised that they “do not have any strong arguments of this kind, but there are two weak facts that could be relevant”. The 1973 paper focuses on the universality of the genetic code and the role that molybdenum plays in living organisms (I am likewise working on a history of molybdenum and the origins of life) which is more than one would expected given the abundance of molybdenum on the earth’s crust.

Francis Crick and Leslie Orgel. (Circa 1993)

Crick and Orgel used the universality of the genetic code to support the theory of directed panspermia because if life had originated multiple times or evolved from a simpler genetic code one could expect living things to use a slew of genetic codes. Further, if there was only one code, Crick and Orgel reasoned that as organisms evolved they should evolve to use the same codons to code for different amino acids.

We can draw a parallel to language: while many human populations use the same symbols (letters), they combine them in different ways. These different languages use the same alphabets but different combinations of the same symbols to denote different objects (French, Italian, Spanish, Portuguese, Catalan) as opposed to different codes (languages which uses different alphabets like Spanish and Mandarin); however, what we find is analog to a single universal language.

Their most convincing argument was the importance of molybdenum in organic processes and its relative scarcity on Earth. They had argued that living organisms should bear the stamp of the environment in which they originated. Organisms, Crick and Orgel held, would be unlikely to develop a dependency on elements that were extremely rare as organisms that relied on elements which were more abundant would be favored by selection.  An organisms that was able to substitute the rare element for one which has similar biochemical properties but is more frequent would have a clear advantage.

http://blogs.scientificamerican.com/guest-blog/2013/01/09/the-origins-of-directed-panspermia/