Measurement of 14 CO 2 Assimilation in Soils: an Experiment for the Biological Exploration of Mars

Abstract

A method is described for the measurement of 14 CO 2 assimilation by microorganisms in soils. A determination involves exposing soil to 14 CO 2 , pyrolyzing the exposed soil, trapping the organic pyrolysis products on a column of firebrick coated with CuO, combusting the trapped organics by heating, and measuring the radioactivity in the CO 2 produced in the combustion. The detection of significant levels of 14 C in the trapped organic fraction appears to be an unambiguous indication of biological activity. The 14 CO 2 which is adsorbed or exchanged into soils by nonbiological processes does not interfere. The method easily detects the 14 CO 2 fixed by 10 2 to 10 3 algae after light exposure for 3 to 24 hr. Assimilation of 14 C is also demonstrable in dark-exposed soils containing 10 5 to 10 6 heterotrophic bacteria. Possible applications of the method in the biological exploration of Mars are discussed.