The hard part, evolutionarily, was getting from prokaryotic cells to eukaryotic ones, and then getting from single-celled organisms to multicellular ones. Earth is around 4.5 billion years old, a timescale I simply cannot get my head around. Instead, let’s imagine Earth’s history as a calendar year, with the formation of Earth being January 1, and today being December 31 at 11:59 PM. The first life on Earth emerges around February 25. Photosynthetic organisms first appear in late March. Multicellular life doesn’t appear until August or September. The first dinosaurs like eoraptor show up about
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