Bill Bryson talks to Mariella Frostrup

The humorist, language expert and traveller launches his new book A Short History of Nearly Everything. How do we know what is in the centre of the Earth, or what a black hole is, or where the continents were 600 million yeras ago? How did anyone ever figure these things out? He also reports on his trip to Kenya, All the author's royalties from Bryson's African Diary and the publisher, Transworld's profits, will go to CARE International.