British Academy Prizes and Medals announced

It has long puzzled scientists why, after 3 billion years of nothing more complex than algae, complex animals suddenly started to appear on Earth. Now, a team of researchers has put forward some of the strongest evidence yet to support the hypothesis that high levels of oxygen in the oceans were crucial for the emergence of skeletal animals 550 million years ago. The new study is the first to distinguish between bodies of water with low and high levels of oxygen. It shows that poorly oxygenated waters did not support the complex life that evolved immediately prior to the Cambrian period, suggesting the presence of oxygen was a key factor in the appearance of these animals. Dr Rosalie Tostevin, a postdoctoral researcher in the Department of Earth Sciences at Oxford University and lead author of the study, said: 'The question of why it took so long for complex animal life to appear on Earth has puzzled scientists for a long time. One argument has been that evolution simply doesn't happen very quickly, but another popular hypothesis suggests that a rise in the level of oxygen in the oceans gave simple life-forms the fuel they needed to evolve skeletons, mobility and other typical features of modern animals. 'Although there is geochemical evidence for a rise in oxygen in the oceans around the time of the appearance of more complex animals, it has been really difficult to prove a causal link.