Did natural reactors form as a consequence of the emergence of oxygenic photosynthesis during the Archean?

Abstract

The advent of oxygenic photosynthesis changed Earth's surface environment in numerous ways, perhaps most notably by making possible the evolution of large and complex life-forms. Current models suggest that organisms that can perform oxygenic photosynthesis first took hold in isolated marine and freshwater basins, producing local oxygen oases. Here we present calculations that suggest that uranium deposits could have formed at the margins of these basins due to the strong local reductionoxidation gradients. Because of the high abundance of 235 U at this time, these uranium deposits could have formed widespread, near-surface, critical natural fission reactors. These natural reactors would have represented point sources of heat, ionizing radiation, and free radicals. Additionally, they would have far-field effects through the production of mobile short-and long-lived radioactive daughter isotopes and toxic byproducts. It is possible that these fission products provided a negative feedback, helping to limit the proliferation of the cyanobacteria in the Archean environment. Secular decreases in the abundance of 235 U in turn decreased the probability of such deposits forming critical fission reactors during the early Proterozoic.

Radiolytic Synthesis of Cyanogen Chloride, Cyanamide and Simple Sugar Precursors

“…Organic accretion layers accumulated on the surfaces of radioactive mineral grains that have been found in the geological record serve as evidence that organic radiolysis reactions can occur in nature in microenvironments found in close proximity to radioactive mineral grain surfaces. Under the primordial conditions of the Hadean eon when the 235 U isotope was much more abundant, so‐called natural nuclear reactors that can promote self‐sustaining nuclear fission chain reactions may have been relatively commonplace . Over a dozen individual fission zones are known from the Oklo locality in Gabon ,.…”

“…Under the primordial conditions of the Hadean eon when the 235 U isotope was much more abundant, so‐called natural nuclear reactors that can promote self‐sustaining nuclear fission chain reactions may have been relatively commonplace . Over a dozen individual fission zones are known from the Oklo locality in Gabon ,. In contrast to the uranium deposits formed by oxygen‐driven precipitation like those found at Oklo, Hadean radioactive seams would have been formed via hydrodynamic sorting of uranium‐rich source rocks, such as uraninite, without need of intermediate precipitation steps ,.…”

Did natural fission of 235U in the earth lead to formation of the supercontinent Columbia?

“…Adam (2007) described possible effects of radiation from various sources on the origin of life on the early earth. Coogan and Cullen (2009) discussed the possibility of fission in pitchblende trapped in the sticky mats of stromatolites.…”

Prebiotic Geochemical Automata at the Intersection of Radiolytic Chemistry, Physical Complexity, and Systems Biology

“…There are differing opinions about the likelihood that the early Earth crust was highly differentiated or closer in composition to the primitive mantle [97][98][99]. The only requirement seems to be that there were at least some areas of the Earth's surface, even relatively small areas, with felsic rock types such as granites that concentrated uranium minerals within a few hundred million years of Earth's formation [100][101][102]. These rocks would then have been weathered and reworked just as they have been throughout most of Earth's geologic history.…”