Radioactivity was discovered in 1896 by French physicist Henri Becquerel.By 1907 study of the decay products of uranium (lead and intermediate radioactive elements that decay to lead) demonstrated to B. Boltwood that the lead/uranium ratio in uranium minerals increased with geologic age and might provide a geological dating tool.
But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.Yet few people know how radiometric dating works or bother to ask what assumptions drive the conclusions. This figure wasn’t established by radiometric dating of the earth itself. Radiohalos shouldn’t exist, according to conventional wisdom!Though they are very tiny, polonium radiohalos have a huge message that cannot be ignored.This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life.For example, about 1.5 percent of a quantity of Uranium 238 will decay to lead every 100 million years.