I would like to widen people's awareness of the tremendous timespan lying ahead - for our planet, and for life itself. Most educated people are aware that we are the outcome of nearly four billion years of Darwinian selection, but many tend to think that humans are somehow the culmination. Our Sun, however, is less than halfway through its lifespan.

It will not be humans who watch the Sun's demise, six billion years from now. Any creatures that exist then will be as different from us, as we are from bacteria or amoebae. Our concern with Earth's future is, understandably, focused upon the next 100 years at most - the lifetimes of our children and grandchildren. But awareness of this longer time horizon, and the immense potential that human actions in this century could foreclose, offers an extra motive for proper stewardship of this planet.

Martin Rees is author of books including Our Cosmic Habitat (buy this book from Amazon (UK) or Amazon (USA)), and Just Six Numbers: The Deep Forces That Shape the Universe (buy this book from Amazon (UK) or Amazon (USA)). See his website.