How old is the Earth? What is the scale of natural history?

Like many people, I find the numbers involved hard to visualize. The Earth formed about 4.6 billion years ago. That's a big number. Dinosaurs died out 65 million years ago. That's a big number too. Humans left Africa 70 thousand years ago. Smaller, but still a pretty big number.

Let's visualize Earth's history in a time scale that we all have an intuitive grasp of, from our own experience: one year. What follows is an extremely brief history of Earth, condensed into one year.

• January 1st: The Earth forms
• Feb/March: First life appears somewhere in here
• Late March: Photosynthesis evolves
• Late June: Atmosphere is starting to oxygenate
• Mid August: Eukaryotic cells
• Late September: Multicellular life
• Mid November: The Cambrian Explosion - many species evolve
• Late November: Some species begin to move onto land

December

• 3rd: Carboniferous period - there are trees, tetrapods, insects, sharks.
• 8th: The supercontinent Pangaea forms.
• 14th: Dinosaurs! And mammals too.
• 17th: Pangaea breaks up.
• 26th (evening): Dinosaurs go extinct.

December 31st

• Noon(ish): Last common ancestor of humans and chimpanzees.
• 7pm: Use of stone tools by Australopithecus.
• 11:37pm: Homo sapiens.
• 11:52pm: Humans migrate out of Africa.
• 11:57pm: Neanderthals die out.
• 11:58pm: Humans have reached South America, and now inhabit all continents.

Final Minutes (measured in seconds before midnight)

• 70 seconds: Agriculture develops in the middle east.
• 52-45 seconds: Sumerian civilization. Writing invented.
• 32 seconds: Pyramids built at Giza.
• 14 seconds: Roman empire under Julius Caesar.
• 5 seconds: The Renaissance.
• 4 seconds: Europeans colonize North America.
• 3 seconds: Newton, the Elizabethan era.
• 2 seconds: The Industrial Revolution.
• 1 second: Telephone, light bulb.

At last, we arrive at midnight - the present day. Homo sapiens have existed for less than half an hour. All of recorded human civilization has happened in the last minute. You, and everyone now alive, was born within the last second. You very likely have less than half a second left to live. Make the most of it.