Abstract
In the terrestrial dipolar magnetic field, magnetic circular dichroism (MCD) of UV sunlight by paramagnetic O(2) in an Archean atmosphere (mostly CO(2) and N(2)) results in circular polarization anisotropy (~ 10(-10)). This is used to calculate enantiomeric excess (EE~10(-13)) of glyceraldehyde (3-carbon sugar) with a model that includes racemic production and asymmetric photolysis of its enantiomers. The sign and magnitude of enantiomeric excess (EE) vary with the Earth's latitude. Unlike random noise fluctuation in spontaneous mirror symmetry breaking (SMSB) models, the sign of EE is deterministic and constant over large areas of prebiotic Earth. The magnitude is several orders greater than the mean amplitude of stochastically fluctuating EE. MCD could provide the initial EE for growth of homochirality by asymmetric autocatalysis.