Imagine an alien spaceship lowering cameras to Earth. Each captures only a few square metres at a time. The first zooms in on the Kalahari desert. The second takes a snap of the Mongolian steppes. A third is lowered over Antarctica, and the fourth hovers over a city and films just a few square metres of grass and a dog peeing up against a tree. What impression would the aliens have? No sign of intelligent life, though primitive life-forms are sporadically present.’
