Carl Sagan proposed this: take the 13.8 billion years since the Big Bang and map it onto a single year. January 1, 00:00:00 is the beginning of everything. December 31, 23:59:59 is right now.
On this scale, 1 cosmic second ≈ 438 years. A cosmic minute is 26,000 years. One cosmic day is 38 million years.
Modern humans showed up roughly 8 minutes before midnight. All of recorded history fits in the last 14 seconds.
Jan 1 · 00:00:00 · The Big Bang. Space, time, energy all at once. In the first fraction of a cosmic second: inflation, matter forming, quarks, protons.
Jan 14 · First stars ignite, pushing hydrogen into helium, into carbon, into everything heavier.
Early galaxies form and grow. Billions of stars live and die, seeding interstellar gas with heavier elements. The elements that will eventually be in your body are being forged.
Mar 16 · The Milky Way begins to take shape.
Aug 31 · The Sun forms from a collapsing cloud of gas in an ordinary corner of the Milky Way.
Sep 1 · Earth forms from the surrounding debris — still molten.
Sep 14 · Life appears on Earth. Single cells. Probably near deep-sea vents.
Sep 30 · Photosynthesis invented. Cyanobacteria start releasing oxygen as a waste product.
Nov 9 · The first eukaryotes. Cells with a nucleus. Much later: mitochondria, sex.
For almost two cosmic months, Earth is just single cells doing their business.
Dec 5 · The Cambrian explosion. Most major animal body plans appear in a geological blink.
Dec 14 · First land plants.
Dec 17 · Amphibians crawl onto land.
Dec 20 · Dinosaurs rise.
Dec 26 · Asteroid. Non-avian dinosaurs go extinct. Mammals get their turn.
Dec 30 · Whales return to the sea. Primates diversify.
Dec 31 · 08:02 · our lineage splits from chimpanzees.
Dec 31 · 23:52 · Homo sapiens appears in Africa (~300,000 years ago).
Dec 31 · 23:58:30 · Humans leave Africa.
Dec 31 · 23:59:32 · cave paintings at Lascaux.