Churchill's Iron Curtain speech about the Cold War, the Sharpeville massacre in South Africa which radicalised many anti-apartheid movements and we hear from a man whose relatives were killed when police bombed the home of African-American radicals in the US. Plus how Nauru became a Pacific island limbo for asylum seekers and the first man to dive to the deepest point on the planet - the bottom of the Mariana Trench. We'll also hear from a BBC science correspondent about why we know more about space than the deepest depths of the ocean.