Fig. 4.

Schematic model showing the topmost layer of Earth’s semiconducting mineral coating together with PS II for harvesting and transforming solar energy. This coating lies parallel to the core, mantle, and crust, but clearly represents a vanishingly small amount of mass compared with these major Earth components/layers. Nevertheless, the average abundances of Mn in the core, mantle, and crust have low values, as indicated in this figure, while Mn is extraordinarily concentrated in the ultrathin layer of mineral coatings. These coatings, together with the PS II protein complex in oxygenic photosynthetic organisms, are believed to be responsible for harvesting and transforming solar energy in the geosphere and biosphere, respectively, which broadens the pathways for utilizing solar energy from the well-known organic world to the newly discovered mineral semiconductor world.