Mineral photoelectrons and their implications for the origin and early evolution of life on Earth

Energy is the key issue of all life activities. The energy source and energy yielding pathway are the key scientific issues of the origin and early evolution of life on Earth. Current researches indicate that the utilization of solar energy in large scale by life was an important breaking point of the early evolution of life on Earth and afterwards life gradually developed and flourished. However, in the widespread biochemical electron transfer of life activities, it is still not clear whether the electron source is sun or how electrons originated from sun. For billions of years, the ubiquitous semiconducting minerals in epigeosphere absorb solar energy, forming photoelectrons and photoholes. In reductive and weak acidic environment of early Earth, when photoholes were easily scavenged by reducing matters, photoelectrons were separated. Photoelectrons could effectively reduce carbon dioxide to organic matters, possibly providing organic matter foundation for the origin of life. Photoelectrons participated in photoelectron transfer chains driven by potential difference and transfer into primitive cells to maintain metabolisms. Semiconducting minerals, by absorbing ultraviolet, also protected primitive cells from being damaged by ultraviolet in the origin of life. Due to the continuous photoelectrons generation in semiconducting minerals and utilization by primitive cells, photoelectrons from semiconducting minerals' photocatalysis played multiple roles in the origin of life on early Earth, such as organic synthesis, cell protection, and energy supply. This mechanism still plays important roles in modern Earth surface systems.