Are fission tracks in enantiomorphic minerals a key to the emergence of homochirality?
published: Jan 1, 2017
With regard to the origin of life in general and to the emergence of biomolecular homochirality in particular, any putative role of naturally etched nuclear particle tracks, as for example fission tracks under early Precambrian weathering conditions, has not yet been addressed. Especially capillary tubes formed by chemical etching of fission tracks in enantiomorphic minerals, are worth to be considered as a source of chiral enrichment of amino acids and other biomolecules. However, of the more than 40 crystalline materials tested for fission-track dating only quartz belongs to an enantiomorphic crystallographic class. The present article reviews published etching conditions for fission tracks in quartz, and presents new experimental tests of these etching conditions, as well as a first attempt to reveal fission tracks in nepheline which is also enantiomorphic. For this purpose, thin slices of quartz cut perpendicular to the crystallographic c-axis, and randomly orientated crystals of nepheline were mounted in epoxy resin, ground and polished. Uranium bearing Durango apatite and pieces of uranium doped glass IRMM-540 were attached to the polished quartz slices and nepheline mounts, and irradiated together with thermal neutrons in the FRM II Reactor (Forschungs-neutronenquelle Heinz Maier-Leibnitz II, TU Munich, Garching, Germany) to produce latent fission-tracks on external mineral surfaces. The measured thermal neutron fluence was 2 × 1015 cm–2. Subsequent etching experiments partly confirm published etching results for quartz – at least with regard to the mixture of 7 g KOH +5 g NaOH +5 g H2 O at 145 °C –, but it was not possible to reveal fission tracks in nepheline with diluted hydrofluoric acid at ambient temperature. This might be due to a low thermal stability of latent fission tracks in nepheline that causes fast and complete track fading at low temperatures (< 60 °C). Many other minerals with enantiomorphic crystal symmetry have not yet been evaluated with regard to their ability to produce chiral capillary tubes by chemical etching of fission tracks. In view of the importance of molecular chirogenesis for the origin of life, such investigations could open a new field of stimulating research.