Natural nuclear fission reactors: time constraints for occurrence, and their relation to uranium and manganese deposits and to the evolution of the atmosphere

Gauthier-Lafaye, F.; Weber, F.

doi:10.1016/s0301-9268(02)00163-8

Cited by 109 publications

(112 citation statements)

References 38 publications

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“…Thus, our organic carbon isotope analyses ( Fig. 1; see Table S2 for full list of data), similar to previous determinations from the Francevillian of Gabon (34), show the beginning of a decrease in δ 13 C at the base of the FB1c unit, with a further decrease through the FC unit with quite depleted values (down to −46 per mil) in the FD unit. These data can be compared with the coupled inorganic and organic carbon isotope record from the contemporaneous Fennoscandia of Arctic Russia (33), showing that the Lomagundi event began before the deposition of the Francevillian sequence.…”

Section: Resultssupporting

confidence: 88%

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Canfield

Ngombi-Pemba

Hammarlund

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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123

139

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The oxygen content of Earth's atmosphere has varied greatly through time, progressing from exceptionally low levels before about 2.3 billion years ago, to much higher levels afterward. In the absence of better information, we usually view the progress in Earth's oxygenation as a series of steps followed by periods of relative stasis. In contrast to this view, and as reported here, a dynamic evolution of Earth's oxygenation is recorded in ancient sediments from the Republic of Gabon from between about 2,150 and 2,080 million years ago. The oldest sediments in this sequence were deposited in well-oxygenated deep waters whereas the youngest were deposited in euxinic waters, which were globally extensive. These fluctuations in oxygenation were likely driven by the comings and goings of the Lomagundi carbon isotope excursion, the longest-lived positive δ 13 C excursion in Earth history, generating a huge oxygen source to the atmosphere. As the Lomagundi event waned, the oxygen source became a net oxygen sink as Lomagundi organic matter became oxidized, driving oxygen to low levels; this state may have persisted for 200 million years.GOE | Paleoproterozoic | marine chemistry | Mo isotope | trace metal

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Section: Resultssupporting

confidence: 88%

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Canfield

Ngombi-Pemba

Hammarlund

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

123

139

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“…Observation at the Oklo natural reactors [23] indicates that the highest grade uranium ore in sandstone always coexists with hematite and illite [24]. Thus, ironrich minerals in the rock play crucial roles in both transport and neutronics aspects.…”

Section: Compositions Of Rock and Groundwatermentioning

confidence: 99%

Conditions for criticality by uranium deposition in water-saturated geological formations

Liu

Ahn

Hirano

2014

Journal of Nuclear Science and Technology

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This study focuses on neutronic analysis to examine the criticality conditions for uranium depositions in geological formations resulting from geological disposal of damaged fuels from Fukushima Daiichi reactors. MCNP models are used to evaluate the neutron multiplication factor (k eff ) and critical mass for various combinations of host rock and geometries. It has been observed that the k eff for the deposition become greater with (1) smaller concentrations of neutron-absorbing materials in the host rock, (2) larger porosity of the host rock, (3) heterogeneous geometry of the deposition, and (4) greater mass of uranium in the deposition. This study has revealed that the planar fracture geometry applied in the previous criticality safety assessment for geological disposal would not necessarily yield conservative results against the homogeneous uranium deposition.

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“…Indeed, the conditions that favor the formation of concentrated deposits of uranite necessary to achieve criticality are thought to have been created by a redox boundary produced by biology (Gauthier-Lafaye and Weber, 2003). Uranium is soluble under slightly oxic conditions and when reduced it precipitates, usually as uranite.…”

Section: Natural Fission Reactorsmentioning

confidence: 99%

Ionizing Radiation and Life

2011

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Ionizing radiation is a ubiquitous feature of the Cosmos, from exogenous cosmic rays (CR) to the intrinsic mineral radioactivity of a habitable world, and its influences on the emergence and persistence of life are wideranging and profound. Much attention has already been focused on the deleterious effects of ionizing radiation on organisms and the complex molecules of life, but ionizing radiation also performs many crucial functions in the generation of habitable planetary environments and the origins of life. This review surveys the role of CR and mineral radioactivity in star formation, generation of biogenic elements, and the synthesis of organic molecules and driving of prebiotic chemistry. Another major theme is the multiple layers of shielding of planetary surfaces from the flux of cosmic radiation and the various effects on a biosphere of violent but rare astrophysical events such as supernovae and gamma-ray bursts. The influences of CR can also be duplicitous, such as limiting the survival of surface life on Mars while potentially supporting a subsurface biosphere in the ocean of Europa. This review highlights the common thread that ionizing radiation forms between the disparate component disciplines of astrobiology.

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Natural nuclear fission reactors: time constraints for occurrence, and their relation to uranium and manganese deposits and to the evolution of the atmosphere

Cited by 109 publications

References 38 publications

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Conditions for criticality by uranium deposition in water-saturated geological formations

Ionizing Radiation and Life

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