Organic Protomolecule Assembly in Igneous Minerals
C-H stretching bands in the infrared spectrum of single crystals of nominally high purity, laboratory-grown MgO and of natural upper mantle olivine provide an "organic" signature that closely resembles the symmetrical and asymmetrical C-H stretching modes of aliphatic -CH2- units. The C-H stretching bands indicate that H20 and CO2, dissolved in the matrix of these minerals, converted to form H2 and chemically reduced C, which in turn formed C-H entities, probably through segregation into defects such as dislocations. Heating causes the C-H bonds to pyrolyze and the C-H stretching bands to disappear, but annealing at 70 C causes them to reappear within a few days or weeks. Modeling dislocations in MgO suggests that the segregation of C can lead to Cx chains, x less than or equal to 4, with the terminal C atoms anchored to the MgO matrix by bonding to two U. Allowing H2 to react with such Cx chains leads to [O2C(CH2)2CO2] or similar precipitates. It is suggested that such Cx-Hy-Oz entities represent protomolecules from which derive the short-chain carboxylic and dicarboxylic and of the medium-chain fatty acids that have been solvent-extracted from crushed MgO and olivine single crystals, respectively. Thus it appears that the hard, dense matrix of igneous minerals represents a medium in which protomolecular units can be assembled. During weathering of rocks the protomolecular units turn into complex organic molecules. These processes may have provided stereochemically constrained organics to the early Earth that were crucial to the emergence of Life.