2020 Volume 129 Issue 6 Pages Cover06_01-Cover06_02
A large quantity of external energy is required to synthesize various building blocks of life (BBLs) in order for life to emerge. Solar energy is too weak to drive prebiotic chemical evolution and no energy is supplied at night. Therefore, other sources of energy are needed. Among those external energy sources are natural nuclear reactors, which are thought to have existed ubiquitously in the surface environment of the Hadean Earth. The decay heat of uranium and ionizing radiation from natural nuclear reactors played an important role in promoting prebiotic chemical evolution. Such chemical evolutional reactions are difficult to achieve with solar energy or heat from magma alone. In other words, the initial process towards the emergence of life on the Hadean Earth was probably driven by ionizing radiation. After a natural nuclear reactor and a geyser combined to form a material-energy circulation system, abundant energy allowed various processes of trial and error to proceed toward achieving the emergence of early life. In this way, the functions of metabolism and self-replication were created. The geyser eruptions produced micron-sized droplets, which were released into the atmosphere to form the most primitive cells. Repeated material circulations and geyser eruptions created various combinations of BBLs, including more complex membranes. The wide variety of primitive cells released to the ground eventually led to a new evolutionary path on the Earth's surface. The proto cells, away from the powerful and abundant energy supplying natural nuclear reactors, would eventually have acquired new capabilities to utilize solar energy for life to survive. The cover, depicting a natural nuclear reactor in contrast to the Sun, is a scene from the CG movie series “The Whole History of the Earth and Life,” which presents the emergence, coevolution, and future of the Earth and life1).
1) YouTube; https://www.youtube.com/c/冥王代生命学の創成 (in Japanese) or https://www.youtube.com/c/HadeanBioscience (in English) [Cited 2020/10/27].