"I 'd like to know how a fission reaction was supposedly possible in the first place . This would be hard to achieve using only light water and ( today 's ) natural uranium ( at about 0.7 % U-235 ) ."
"Well , since the composition of the uranium body when it was a natural reactor was n't the same as today 's natural uranium , it does n't matter . What is important was the composition of the ore back then . Since U-238 has a half-life of 4.468E+9 years and U-235 has a half-life of 7.038E+8 years , it is apparent that the U-235 decays much more rapidly . It stands to reason that the The relative percentage of U-235 to U-238 was higher in the past . It also stands to reason that thee was more uranimum present at the time that the natural reactors were active . About 2 billion years ago the U-235 was about 3 % or more of the composition of the uranium ."
"I 'd like to know how a fission reaction was supposedly possible in the first place ."
"Well , since the composition of the uranium body when it was a natural reactor was n't the same as today 's natural uranium , it does n't matter"