Insights gained through cultivation and genomics have revealed that energy harvesting is accomplished by diverse, yet modular arrangements of enzymes. However, a number of possible energy sources and pathways are not yet observed in extant metabolisms. In addition, outside of energy metabolism, a substantial number of possible molecular interconversions are also not observed in biology. Given that life may have been on Earth for just over 4 billion years, how can we explain the lack of energy and metabolic pathway utilization?
We seek to enumerate energetically feasible, but unknown metabolisms. Further, we seek to contextualize and interpret this enumeration in an evolutionary context. Finally, we seek to use this knowledge as a basis for conjecture on what may have been, or may not have been, the energy sources and metabolic foundation for the origin of life.