As we approach the end of the human calendar year, it seems appropriate to revisit the calendar of life. Current scientific evidence indicates that life first evolved on Earth about 3.6 billion years ago, 10 billion years after the Big Bang and 1 billion years after the Earth, itself, formed. If we were to condense this history of life into one human calendar year, each day would represent 10 million years, each hour would equal 417,000 years, each minute would amount to 7000 years and each second would cover 117 years.
Using this calendar of life, the first bacteria (chemoautotrophic and cyanobacteria) appear in Earth's primordial oceans at 12 AM on January 1. By the beginning of June, eukaryotic cells (possessing intracellular nuclei and organelles) appear and, by October 15, shelled marine life and multicellular soft-bodied marine organisms (the Ediacaran fauna) inhabit the ancient seas. Near mid November, life crawls from the sea and, throughout the last 10 days of November, sharks, boney fish, ferns, primitive amphibians, web-spinning spiders and flying insects evolve. The first week of December brings horseshoe crabs, frogs, primitive reptiles and conifers to our planet.
Dinosaurs reign from December 8 until noon on December 25. Crocodilians, turtles ancestral monotremes, shrew-like mammals, archaeopteryx and flowering plants all appear by mid December, followed by snakes, ants, social bees, marsupials and broadleaf trees during the third week of the month. December 26-27 brings ancestral primates, ancestral elephants, cone snails, bats, canids, felines, rodents, early cetaceans (whales, dolphins) and ancestral horses, camels, mustelids, tapirs and sirenians (manatees and dugongs). From December 28 into December 29, grass, ancestral pigs, mastadons and North American megafauna appear and, on December 30, giraffes, okapis, hippos, true elephants and pronghorn evolve as pinnipeds diverge from the bear line. Cattle, bison, goats and sheep all turn up on December 31. At about 3AM on that last day, gorillas split from the hominid line and chimps do the same by 8 AM; Australopithecus appears just after noon. Homo habilis evolves around 6 PM and Homo erectus follows by 8 PM. During the last hour of the last day, Denisovans, Neanderthals, polar bears and arctic fox appear and humans finally grace the scene 18 minutes before midnight; no living human has been around for more than 1 second.