Interesting read. But he contradicts himself in the final paragraph:
But these will be flimsy souvenirs, almost pathetic reminders of a civilisation that once thought itself the pinnacle of achievement. Within a few million years, erosion and possibly another ice age or two will have obliterated most of even these faint traces. If another intelligent species ever evolves on the Earth - and that is by no means certain, given how long life flourished before we came along - it may well have no inkling that we were ever here save for a few peculiar fossils and ossified relics.
So, given how long life has indeed flourished on Earth, how does he know there has not been an intelligent species here before, millions of years ago? By his own theory, all traces of them would now be gone. The dinosaurs ruled for millions of years and died out 65,000,000 years ago. Thats plenty of time for an intelligent species to evolve, peak, and then disappear without trace, several times over.