A growing number of scientists are discovering that removing top predators from the wild has thrown ecosystems off-kilter, triggering domino effects that scientists are just beginning to understand. NOVA follows scientists who are trying out a simple but controversial solution: returning apex predators — like coyotes, bears and panthers — to their natural environments.
The dome that crowns Florence's great cathedral of Santa Maria del Fiore -- the Duomo -- is a masterpiece of Renaissance ingenuity and an enduring source of mystery. Still the largest masonry dome on earth, it is taller than the Statue of Liberty and weighs as much as an average cruise ship. More than four million bricks could collapse at any moment -- and we still don't understand how its architect, Filippo Brunelleschi prevented it. To test the latest theories, a team of U.S. bricklayers will help build an experimental "mini-Duomo" using period tools and techniques.