How did this continuous chemical reaction that we call "life" first begin? And why did the hellish conditions of the early Earth provide the perfect birthplace? Justin Rowlatt speaks to two scientists with rival theories about the origin of life, both trying to recreate it in their labs - John Sutherland of Cambridge University, and Nick Lane of University College London. Plus the Natural History Museum's Sara Russell shows Justin a rock that is older than the Earth itself - the Winchcombe meteorite.