Geobiochemistry in 2019

Rocks and genomes hold complementary geologic records. Reading these records simultaneously will be enabled as we learn how biochemistry emerged from geochemistry. Results from the first two decades of the twenty-first century have revealed some consequences of this emergence. Evidence shows how metabolism moves toward geochemical opportunities, leaving temporal traces in the coevolution of life and Earth. Geobiochemical echoes persist in the shift of lipid compositions with changes in oxidation state, temperature, and composition, all reflecting the principle that biomolecular function is preserved at the cheapest energetic cost. Analogous thermodynamic consequences are predicted for proteins from metagenomic data. Treating microbes as the average of their protein composition allows calculation of relative stabilities and predictions of community structure from metastable Gibbs energy minimizations. Where might we be after a couple more decades? Here are some possibilities. The principle of preserving function while minimizing cost will yield a thermodynamic basis for microbial ecology. Genomes from cultures or predicted from metagenomes will make it possible to convert ribosomal RNA sequences into cellular compositions, enabling mass-transfer models to simultaneously predict community structure, fluid compositions and mineral assemblages. The possibility of predictive feedback among fluid, mineral, lipid and protein compositions is beguiling. Adopting a geochemical framework for experimental evolution will allow explicit tests of hypotheses linking branch points in the tree of life to events in Earth history. Understanding how life on Earth fits the Earth as a product of geologic history will hone capabilities to anticipate biochemistries of other worlds. At some point it will seem commonplace to combine geologic histories from rock and genomic records, especially if tool development is encouraged.