We map Earth's history into a 12-hour imaginary clock. 4.567 billion years ago, when the Earth first formed, happens at 0:00:00. The first prokaryotic organisms, very simple cells lacking a nucleus, appear rather early, at around 1:49:33. They dominate the planet until the eukaryotic cells, those unicellular organisms containing membrane-bound complex structures, appear between 2.1 and 1.8 billion years ago, or at 6:31:18 in our clock. Complex creatures arrive at 10:35, amphibians and reptiles at 11:04:44, and dinosaurs at 11:24:46, staying for only 25 minutes. It is fascinating to realize that on such a scale, humans have been on the planet merely the last 2 seconds: since 11:59:58.