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

► Natural fission of 235U was a significant source of heat in the earth before about 2 Ga. ► Fission developed depleted Archean lower crust that now has a low heat generation. ► The lower crust is an inaccessible depleted reservoir that accounts for the first lead isotope paradox. ► The earth was cool enough by 2.0-1.8 Ga that widespread networks of orogenic belts could develop. ► Networks of orogenic belts at 1.8 Ga partly generated the supercontinent Columbia.