It is a privilege to speak here today. But I do this with diffidence. That is because I am a physicist – trying to understand only the inanimate world. Much of this still baffles us. But it should be an easy task, compared to the complexities of living things and their ecologies. It is the biologists, ecologists and social scientists who face the most daunting intellectual challenges. Those are the disciplines represented at this meeting.

You may think that, as an astronomer, I worry about asteroid impacts. I do, but not very much. It was such an event 65 million years ago that many think did in the dinosaurs. But the probability of such a catastrophe is 1 in 100,000 each century – no bigger now than it was in the remote geological past.