Searching for Life in the Solar System ... And Beyond
A Research Discussion Meeting
London, UK - 31 October 1996

Can Metasediments record the existence of amino acids?

Stuart R. Boyd, CNRS, France

Ecosystems exhibit long-term stability. The reasons for this are many-fold. Since the ultimate energy source is the sun, the long-term stability of the solar system is of prime importance. Biodiversity is equally important since the richness of species ensures that the demise of one will be replaced by another. However, there is another aspect which is unseen and largely unknown: atmospheric chemistry has evolved over billions of years and, despite recent concerns, there are aspects which are very stable. Biogeochemistry is a branch of the Earth Sciences which studies the effects of life on certain aspects of the planet. The term means different things to different people, and the precise definition, in this context, will be given at conference.

The radiation of species at the Precambrian/Cambrian boundary was possible because the labour of simple organisms, such as bacteria, had so changed the composition of the external envelope of the planet, that the new species had an environment to evolve into.

The precise details of how and when these changes occurred remain unknown. One aspect of environmental evolution involves the biological splitting of inorganic molecules, followed by burial of one fragment in sediments with the partner(s) remaining free, somewhere in the crust,atmosphere or oceans. The buried fragment can be considered as forensic evidence of the 'crime' of a former biochemical cycle. We can measure the age of rocks and also look for biochemical tracers, and thus begin to build up a pattern (in detail) of past events.

As we go back in time, the probability of finding pristine sediments diminishes. Often they have been highly metamorphosed which can result in the 'forensic evidence' becoming ambiguous. In the seminar, the author will provide data which suggest that the ammonium trapped in potassic minerals provides evidence of the former presence of organic matter (amino acids) in highly altered sediments. Similar data have been used to identify rocks which have produced hydrocarbons. Results obtained from the Proterozoic of Scotland (Moine), a sequence of sediments which were heated to the point of melting, will be presented. If there were once, warm little ponds on other planets, where 'biochemical' cycles were operating, then the techniques involved, or others waiting to be discovered, would help in their unveiling.