Mineral radioactivity in sands as a mechanism for fixation of organic carbon on the early Earth.

Irradiation of organic molecules by mineral radioactivity is a feasible alternative to cosmic irradiation to precipitate solid organic carbon-rich matter on the early Earth. Radioactive (uranium- and thorium-rich) minerals have been concentrated at the Earth's surface, and accumulated accretionary coatings of carbon due to irradiation, since early Archean times. The organic accretion process could have occurred at the surface or in the sub-surface, and is independent of a terrestrial or extraterrestrial source for the carbon.