Episode 7 of Fox's Cosmos, entitled "The Clean Room", covered the search behind the age of the Universe. Meteorites found on the Earth surface contain a certain amount of lead, which is actually a decayed form of Uranium. Thus, by measuring the amount of lead, one can determine the age of the rock, and this can be extended to the age of the Earth. Clair Patterson had to build a "Clean Room", a lab that was free of lead contamination so that he could accurately measure the amount of lead in a meteorite.
Lead was a popular ingredient in many products in the middle of the 20th century, from paint to gasoline. Patterson's work help to show that the amount of lead in the environment has been increasing over time, and this helped many industries (such as oil and petroleum) to stop using lead in their products, since it was known to be poisonous. Of course, these industries did not go down without a fight, and hired their own scientists to push their agenda.
Check out Outkast's video for "So Fresh, Co Clean" below, as well as the Storify of the live tweet of the episode.