Half a billion years from now, the Earth has become a very harsh and unforgiving place. Carbon dioxide has disappeared from the atmosphere, photosynthesis has become impossible and plants are extinct. Oxygen, too, is now absent from the air. Average temperatures are approaching 60°C and noon-day equatorial temperatures now exceed boiling point. In the high Arctic a new mountain chain has grown that rivals the Himalayas of our own time, and towards the tops of its north-facing slopes, drizzle reluctantly condenses out of the humid atmosphere to collect in muddy, tepid pools that are the Earth’s only remaining standing water. A few particularly tough Loricifera cling to life here by grazing on bacterial mats and absorbing hydrogen sulphide in place of oxygen. Their time too is drawing to a close as temperatures soar to levels unknown for 5 billion years. Liquid water has become a scarce commodity that will vanish completely in a few more million years, taking the last of Earth’s living things with it.
For almost 5 billion years the Earth maintained a fairly stable temperature because, as the Sun gradually warmed through time, our atmosphere slowly lost its greenhouse gases. However, even a zero level of greenhouse warming is now not low enough to keep our planet cool under the gaze of an ever-warming Sun. To make matters worse, water vapour and methane are now building up rapidly in the atmosphere and a runaway greenhouse is beginning. The long history of good weather on our world is about to come to an end. Life of any kind will soon become impossible and the unique 5 billion-year story of life on Earth will reach its sad conclusion.
Our complex biosphere has outlived that of our sister planet, Nemesis, by less than a billion years. Life on Earth will not even last long enough to suffer the same fate as our sibling. All our water will evaporate into space a billion years before the Moon moves far enough away for our axis to become unstable. The goddess of undeserved good fortune exacts her price from all inhabited worlds but she deploys many different agents of destruction.
I will not finish on such a negative note. Earth and countless other inhabited worlds scattered thinly throughout an unimaginably immense multiverse have given rise to the fragile wonder of life. On Earth we have laughed, loved and wondered at the beauty of the world and the Universe around us. We are part of an extraordinary miracle and I, for one, feel very lucky.