During the 1950s, geophysicists explored the use of other radioactive elements for similar purposes. The first method to yield successful results was the potassium-argon (K/Ar) technique, which can accurately date materials ranging from hundreds of thousands to millions of years old. There was still a gap, however, between the oldest radiocarbon dates and the youngest potassium-argon dates, and it was during just that period of time that some of the more crucial events in human evolution took place. Subsequently, the investigation of the proportions between the radioactive isotopes of elements such as protactinium, rubidium, strontium, thorium, and uranium and their stable end products helped provide a check for the K/Ar estimates and also helped fill in some of the remaining blanks.
At the time, it was reported that the feature would trace Kennedy’s ascent from a politician in the shadow of his president brother, John F. Kennedy, to a strong national leader in his own right. He ran JFK’s successful 1960 presidential campaign and served as both his top adviser and the . Attorney General between 1961 and 1963. He remained in the post for President Lyndon B. Johnson for several months after his brother’s assassination, then resigned to run for the . Senate, representing New York. He went on to campaign for the Democratic presidential nomination on the platform of ending . involvement in the Vietnam War, but was assassinated in June 1968.