This episode is centered the work of Clair Patterson in the middle of the 20th century, who was able to determine the age of the Earth.
Patterson determined an accurate count of lead in zircon particles from meteor craters. With the established half-life of uranium’s radioactive decay to lead, this would be used to estimate the age of the Earth.
Patterson found that his results were contaminated by lead from the ambient environment, required the construction of the first ultra-high clean-room to remove all traces of environmental lead. With these clean results, Patterson was able to estimate the age of the Earth to 4.5 billion years.
Patterson examined the levels of lead in the common environment and in deeper parts of the oceans and Antarctic ice, showing that lead had only been brought to the surface in recent times.
He would discover that the higher levels of lead were from the use of tetraethyllead in leaded gasoline, despite long-established claims by Robert A. Kehoe and others that this chemical was safe. Patterson would continue to campaign against the use of lead, ultimately resulting in government-mandated restrictions on the use of lead.