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Steady decline in the percentage of 235 U in terrestrial uranium made natural fission impossible after about 1.8Ga. Fission before 1.8Ga disturbed the lead isotope system at various places worldwide, such as Oklo, Gabon, and may have caused the first lead isotope paradox. Fission in areas of high uranium concentration may also have generated enough heat to localize sparse Archean and Paleoproterozoic...
Assembly of the supercontinent Columbia at about 1.85–1.90 Ga coincided with several events that affected the entire earth. The oldest worldwide network of orogenic belts formed at the same time. Although some granite–granodiorite (GG) suites had formed earlier, the GG suites became common in the 1.8–1.9 Ga orogenic belts. These suites succeeded the older tonalite–trondhjemite–granodiorite (TTG) suites,...
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