TL;DR: We poisoned ourselves for about half a century.
> The episode describes how science, in particular the work of Clair Patterson (voiced in animated sequences by Richard Gere) in the middle of the 20th century, has been able to determine the age of the Earth.
> Patterson found that his results were contaminated by lead from the ambient environment...
> Tyson goes on to explain that Patterson's work in performing lead-free experiments directed him to investigate the sources for lead. Tyson notes how lead does not naturally occur at Earth's surface but has been readily mined by humans (including the Roman Empire), and that lead is poisonous to humans. 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. Tyson ends by noting that similar work by scientists continues to be used to help alert mankind to other fateful issues that can be identified by the study of nature.
