Brian Stableford 
Walking Shadow 

Paul Heisenberg is mysteriously endowed with the ability to jump through time. Together with thousands of eventual followers, he begins a journey that eventually takes him a billion years into the future. The Earth has been devastated by war with an alien race, and the changes that have resulted from the degradation of the world’s biosphere force him–and others–to rethink their own humanity. His pilgrim’s progress through the coming time is beset by doubts, distractions, and temptations as various voices attempt to distract him from his determination to follow the process through to its end. He eventually witnesses the complete transformation of the Earth, and the evolution of a single omnipotent but mindless Gaean organism. Is intelligence itself just a brief candle, forever doomed to burn out? Or can Paul find some other alternative for his race.