Photoelectrons from minerals and microbial world: A perspective on life evolution in the early Earth

• Semiconducting mineral photocatalysis to evaluate origin and evolution of life.
• New model on the use of solar energy by non-phototrophic microorganisms.
• New insights on energy yielding pathway for life on early Earth.

Fundamental to the origin and evolution of life are the sources of energy and mechanisms of various energy yielding pathways. Recent investigations revealed that the ternary system of microorganisms, minerals and solar light has played a critical role in the history of life on our planet. Solar energy utilization pathway by nonphototrophic microorganisms mediated by semiconducting mineral photocatalysis provides a new concept to evaluate the origin and evolution of life. Semiconducting minerals are ubiquitous on Earth's surface and widely participate in redox reactions following photoelectron–photohole pairs excited by solar light. As photoholes can be easily scavenged by environmental reductive substances and microorganisms possess multiple strategies to utilize extracellular electrons, the highly reductive photoelectrons serve as potential energy source for microbial life. The discovery of this pathway extends our knowledge on the use of solar energy by nonphototrophic microorganisms, and provides important clues to evaluate life on the early Earth.

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