Three women at risk of developing Alzheimer's join a groundbreaking study to prevent the disease while sharing their ups and downs, anxiously watching for symptoms, and hoping they can make a difference. Barb, Sigrid, and Karen all had mothers with Alzheimer's and witnessed firsthand the devastation wrought by the disease, not only on the mind and body but on patients' families. Now, they are all participating in a major study that tracks the health and memory of thousands of people over many years, as researchers hunt for lifestyle changes and medicines that could improve all our chances and ultimately protect the brain and body from one of the world's deadliest diseases.

In the second episode of this two-part series, the search continues for signs of what happened on the day the dinosaurs died. Scientists uncover extremely rare fossils and more evidence that could link the dig site in North Dakota to the asteroid that wiped out the dinosaurs 66 million years ago. Among the fossils are tiny spheres of glass locked in amber. Inside one of the spheres is a speck of rock that appears to be a chemical match to the killer asteroid itself. And scientists uncover one of the most spectacular finds of all: an almost perfectly preserved dinosaur leg. Sir David Attenborough guides us on a search for clues that could provide an unprecedented snapshot of what happened in the dinosaurs' final moments on Earth.