Earth's history in 24 hours
If the whole 4.54 billion years of Earth's history were squeezed into one day, the first life would appear before 6 AM, dinosaurs at about 10:46 PM, and modern humans in the last 6 seconds before midnight. All of recorded history fits in the final tenth of a second. Switch to the universe to see Carl Sagan's famous cosmic calendar.
Earth's history as one day
| Event | When | Time on the clock |
|---|
Find any moment
Why squeeze time into a day?
Numbers like 4.54 billion are too big for anyone to feel. Mapping them onto a day or a year turns them into something familiar. On the one-day clock, one second stands for about 52,500 years, one minute for 3.2 million years and one hour for 189 million years. Dinosaurs ruled for about 167 million years, nearly an hour of the clock, while the whole of human civilization fits in the last tenth of a second.
The idea was made famous by the astronomer Carl Sagan's Cosmic Calendar in his 1977 book The Dragons of Eden and the TV series Cosmos, which squeezed the age of the universe into one calendar year. In that year, the Sun forms in early September, dinosaurs appear around Christmas, and every human who ever lived arrives in the last hours of New Year's Eve.
How the dates were chosen
The ages are standard figures from geology and astronomy: Earth's age of 4.54 billion years comes from radiometric dating of meteorites, and the universe's 13.787 billion years from the Planck satellite. Some early dates, like the first life and the first stars, are still debated and could move by a few hundred million years. That moves them only a few minutes on the clock.
For shorter spans, try the units of time converter, the history of timekeeping or time dilation.
Questions people ask
If Earth's history were 24 hours, when would humans appear?
Modern humans, Homo sapiens, about 300,000 years ago, would arrive about 6 seconds before midnight, at 23:59:54.
When would dinosaurs appear on the 24-hour clock?
The first dinosaurs, about 233 million years ago, appear at about 22:46, and they die out 66 million years ago, at about 23:39.
What is the cosmic calendar?
A way of picturing the 13.8-billion-year history of the universe as one calendar year, made famous by Carl Sagan. The Big Bang is on January 1 and the present is the final second of December 31.
How long is one second on the Earth clock?
About 52,500 years. One minute is about 3.2 million years.