American radiochemist Bertram Boltwood was the first scientist to establish that lead was the final decay product of uranium. He noted that the lead-uranium ratio was greater in older rocks and, acting on a suggestion by Ernest Rutherford, was the first to successfully measure the age of rocks by the decay of uranium to lead, in 1907. He got results of ages of 400 to 2200 million years, the first successful use of radioactive decay by Pb/U chemical dating. Recently, using his research and methods older mineral deposits have been dated to about 4.4 billion years old, close to the best estimate of the age of earth.
His work with the uranium decay series led to the discovery of the parent of radium, a new element that he named ionium. When he isolated it he believed it to be a new intermediate element in the decay chain between uranium and radium. Once the existence of isotopes was established researchers eventually determined that ionium was actually an isotope of thorium.. It was discovered that ionium and thorium-230 are chemically identical..
Ada Hitchins selectively extracted uranium from ore samples to create purified uranium preparations and established a half-life for ionium. Her research also showed that there was a steady rate of increase in the amount of radium in her uranium solutions, the first direct experimental evidence that radium was formed by the decay of uranium. Her results were published in 1915..