Abstract
C-H stretching bands, nu (CH), in the infrared spectrum of single
crystals of nominally high purity, of laboratory-grown MgO, and of
natural upper mantle olivine, provide an örganic" signature that
closely resembles the symmetrical and asymmetrical C-H stretching
modes of aliphatic -CH2 units. The nu (CH) bands indicate that H2O
and CO2, dissolved in the matrix of these minerals, converted to
form H-2 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 nu (CH) hands to disappear,
but annealing at 70 degreesC causes them to reappear within a few
days or weeks. Modeling dislocations in MgO suggests that the segregation
of C can lead to C-x chains, x = 4, with the terminal C atoms anchored
to the MgO matrix by bonding to two O-. Allowing H-2 to react with
such C-x chains leads to O2C(CH2)(2)CO2 or similar precipitates.
It is suggested that such C-x-H-y-O-z entities represent protomolecules
from which derive the short-chain carboxylic and dicarboxylic and
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.
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