Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light-years, which is a great deal more than merely saying it makes it sound. “We may be only one of millions of advanced civilizations. It's a wonder that anything at all can survive in such a pummeled and unsettled environment. And throughout the whole, about three times every minute, somewhere on the planet there is a flash-bulb pop of light marking the impact of a Manson-sized meteor or one even larger. Mountains rise and melt away, ocean basins come and go, ice sheets advance and withdraw. Throughout this greatly speeded-up day continents slide about and bang together at a clip that seems positively reckless. The whole of our recorded history, on this scale, would be no more than a few seconds, a single human lifetime barely an instant.
Humans emerge one minute and seventeen seconds before midnight. At twenty-one minutes to midnight they vanish and the age of mammals begins. and hold sway for about three-quarters of an hour. Dinosaurs plod onto the scene just before 11 P.M. Thanks to ten minutes or so of balmy weather, by 10:24 the Earth is covered in the great carboniferous forests whose residues give us all our coal, and the first winged insects are evident.
Soon after, with less than two hours left in the day, the first land creatures follow. trilobites swim onto the scene, followed more or less immediately by the shapely creatures of the Burgess Shale. Then, finally, the first sea plants appear, followed twenty minutes later by the first jellyfish and the enigmatic Ediacaran fauna first seen by Reginald Sprigg in Australia. Not until almost 8:30 in the evening, with the day five-sixths over, has Earth anything to show the universe but a restless skin of microbes. “If you imagine the 4,500-bilion-odd years of Earth's history compressed into a normal earthly day, then life begins very early, about 4 A.M., with the rise of the first simple, single-celled organisms, but then advances no further for the next sixteen hours.
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