If you consider our place in the history of the Universe, it is easy to see humans as an insignificant temporal speck, flickering in an unspeakably vast cosmos.

One common analogy illustrates this by telling the story of our planet’s 4.7-billion-year history as if it were the 24 hours of a single day. If you assume that the Earth coalesced an instant after midnight, it took around four hours for the first life to appear: microscopic organisms clustered around hydrothermal vents beneath young oceans. It took five more hours for photosynthesis to begin—and until midday for the atmosphere to become rich in oxygen. By 18:00 we had sexual reproduction; at 22:00 the first ever footprints appeared on land, left by lobster-sized sort-of-centipedes; and by 23:00 the dinosaurs had arrived, only to exit 40 minutes later alongside three-quarters of Earth’s species in the planet’s fifth mass extinction.

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