Magnetic Circular Dichroism in Archean Stratospheric Oxygen: Enantiomeric Excess of Amino Acids Produced in Volcanic Plumes

While there is consensus that Archean atmosphere was anoxic with O-2 pressure, p(O-2) <10(-6) PAL (present atmospheric level) at sea-level, evidence suggests that p(O-2) at stratospheric altitudes of 10-50 km was orders of magnitude higher, a result of photodissociation of CO2 by UVC sunlight and incomplete mixing of O-2 with other gases. Molecular O-2 is paramagnetic due to triplet ground state. Magnetic circular dichroism (MCD) by stratospheric O-2 is examined in earth's magnetic field and shows maximum circular polarization (I+ - I-) at altitude of 15-30 km (I+/I- is intensity of left/right circularly polarized light). While (I+ - I-)/(I+ + I-) is small (similar to 10(-10)), it is an unexplored source of enantiomeric excess (EE) by asymmetric photolysis of amino acid precursors produced in volcanic eruptions. The precursors reside in stratosphere for periods of over a year due to relative absence of vertical transport. Due to negligible thermal gradient across equator, they are trapped in the hemisphere where they are produced, with interhemispheric exchange time of over a year. The precursors diffuse through altitudes of maximum circular polarization before getting hydrolyzed on ground to amino acids. Enantiomeric excess of similar to 10(-12) is calculated for precursors and amino acids. While small, this EE is orders of magnitude higher than predicted (similar to 10(-18)) by parity violating energy differences (PVED) and could be the seed for growth of biological homochirality. Preferential crystallization (PC) is described as a plausible mechanism for amplification of solution EE of some amino acids from 10(-12) to 10(-2), for period of several days.