Radioactivity OTL was discovered by Madame Curie and by Becquerel in the early 20th century. Given that it is a famous example of a serendipitous discovery in Becquerel's case, could a similar discovery have happened years before? The Joachimsthal mines in what was Austria have been producing uraninite along with their eponymous currency-grade silver since the 16th century, so the original source of the discovery had been present long before the actual discovery. What would it take to have an eighteenth-century or earlier scientist formulate a comprehensive theory of radioactivity?