Five centuries ago, the Age of Exploration and Europe's imperial colonization of far-off lands was launched by a revolution in ship design that made long-distance ocean voyages practical. But exactly how this momentous innovation happened eludes historians. Now, the excavation of a rare intact wreck discovered off the coast of Sweden offers vital new clues to a maritime mystery. 

Along with other clues gleaned from the wreckage, the figurehead and gun carriages suggest that this could be the flagship of a Danish king named Hans. The monarch was famous for building a large naval fleet, led by a massive warship known as the Gribshunden, the Griffen Dog.

NOVA investigates the story of cannabis from the criminalization that has disproportionately harmed communities of color to the latest medical understanding of the plant. What risks does cannabis pose to the developing brain? How much do we know about its potential medical benefits? As cannabis becomes socially accepted and state-legalized, scientists are exploring its long-term health consequences.