Ninety-three million years ago, Earth was a reshuffled jigsaw of continents, a hothouse where the average temperature was nearly twice that of today.

Palm trees grew in what would be Alaska, large reptiles roamed in northern Canada and the ice-free Arctic Ocean warmed to the equivalent of a tepid swimming pool.

So our planet was balmy -- but hardly a biological paradise, for it was whacked by a mass die-out. The depths of the ocean suddenly became starved of oxygen, wiping out swathes of marine life.