From the plane, Hiroshima looked like a roiling, bubbling sea of black smoke and fire. A small amount of fissile material was responsible for the devastation; 98.62 percent of the uranium in Little Boy was blown apart before it could become supercritical. Only 1.38 percent actually fissioned, and most of that uranium was transformed into dozens of lighter elements. About eighty thousand people were killed in Hiroshima and more than two thirds of the buildings were destroyed because 0.7 gram of uranium-235 was turned into pure energy. A dollar bill weighs more than that.
