David Khan asked:
How does radio carbon dating work?
Preston - It works because you have carbon 14 which is a heavier form of carbon 12 formed in the upper atmosphere with the bombardment of the carbon by cosmic rays and other bits of radiation. We know how much of that is being formed today. Therefore by looking at the ratio of carbon 14 to the carbon 12 in anything that has taken carbon in: any plant or animal that was living in the past you can measure the level of the carbon 14 thatís left. That way you can infer how long it has been dead since that carbon 14 has decayed.
Chris - Because it stops taking the radioactive form in the minute it dies. Therefore the radioactive carbon in it must decline after death and therefore working out how much is in there tells you how it died: how long ago. Because we know how long the carbon takes to disappear.
Preston - Exactly