Bertram Boltwood

Bertram Borden Boltwood was an American pioneer of radiochemistry who became a professor at Yale University and in 1910 was appointed chair of the first academic department of radiochemistry. He established that lead was the final decay product of uranium, noted that the lead-uranium ratio was greater in older rocks, and in 1907, acting on a suggestion from Ernest Rutherford, became the first to measure the age of rocks from the decay of uranium to lead, obtaining results of 400 to 2200 million years. His work on the uranium decay series also led to his discovery of a new element he named ionium, later shown to be an isotope of thorium.