5 MINERALS AND THE EMERGENCE OF LIFE

Abstract

Metal-bearing minerals are an integral part of almost all “metabolism-first”-type scenarios for the emergence of life which consider that life is better defined by what it does than what it is made from. Since metals are formidable catalysts, these scenarios stipulate that early metabolic reactions (and prominently the reduction of CO 2 to yield biomass) were performed by (mainly transition) metals contained in certain minerals. Metabolismfirst scenarios stand in opposition to primordial soup hypotheses which envisage prebiotic synthesis of organic molecules as building blocks for life to be the salient feature enabling life to come into being. A critical analysis of the historical roots of these emergence of life hypotheses highlights fundamental inconsistencies prompting us to appeal to basic thermodynamic principles to provide rigorous guidelines for developing contradiction-free models. Combining these guidelines with our present-day understanding of biological energy conversion, arguably the process most fundamental to all life, strongly suggests an expansion of previous mineral-based scenarios to include processes converting environmental redox tensions into phosphate-group-transfer disequilibria, i.e., the quintessential free energy converting mechanism of extant life. Based on their reported physicochemical and electrochemical properties, iron- (together with other transition metal-) based layered double oxyhydroxide (Fe-LDH) minerals such as fougerite are promising candidates to afford the required capacities and therefore may render previous mineral-based scenarios compliant with thermodynamic strictures.