EAS Spring 2018 Seminar Series Presents: Dr. Nita Sahai, University of Akron

The focus of our work is to determine the constraints placed by atmosphere-water-rock interactions on the environmental conditions for self-assembly of the molecular building blocks of the earliest like-like entities, “protocells.” 

We have addressed the problem that modern geochemical concentrations of total dissolved phosphate (PT) and Mg2+ are much lower than those are required for non-enzyamtic (prebiotic) RNA synthesis, while Mg2 and Ca2+ concentrations are too high for membrane stability, so how did life emerge on early Earth? 

We used a geochemical thermodynamic modeling approach, to show that a single, globally-occurring geological process of komatiite rock weathering and evaporation of the resulting solutions under specific partial pressures of atmospheric CO2 (PCO2) can quantitatively provide the PT, Mg2+ and Ca2+ concentrations required for nucleotide synthesis, RNA polymerization and protocell-membrane stability. 

Conversely, the biologically-required concentrations of PT, Mg2+ and Ca2+ place constraints on the PCO2 levels on early Earth compared to previous estimates ranging over five orders of magnitude. Using these environmental constraints on Mg2+ and Ca2+ concentrations, we examined the stability and evolution of simple protocell membranes from pure single chain amphiphile (SCA) compositions through mixed SCA-phospholipid (PL) to pure PL compositions found in modern cells. 

We showed that, rather than acting being toxic, the divalent cations promoted evolution of the membranes towards more modern compositions. We also found that RNA oligomer synthesis is possible even at much lower concentrations of Mg2+ than previously reported, well within the concentration range constrained by the atmosphere-water-rock interactions. 

Thus, we have used a geochemical modeling approach to create the components of a simple protocell under geochemically plausible conditions.