The stupendous time spans of the evolutionary past are not part of common culture–except among some creationists and fundamentalists. But most educated people, even if they are fully aware that our emergence took billions of years, somehow think we humans are the culmination of the evolutionary tree. That is not so. Our Sun is less than half way through its life. It is slowly brightening, but Earth will remain habitable for another billion years. However, even in that cosmic perspective—extending far into the future as well as into the past—the twenty-first century may be a defining moment. It is the first in our planet’s history where one species—ours—has Earth’s future in its hands and could jeopardise not only itself but also life’s immense potential.
Martin Rees, ‘Foreword’, in Nick Bostrom and Milan M. Ćirković (eds.), Global Catastrophic Risks, Oxford, 2008, p. xi