What it does
Earth is about 4.54 billion years old. Numbers that big are hard to picture, so geologists split the time into named pieces and teachers often squeeze the whole story into something familiar, like one calendar year.
- Time scale. The drawing shows the four eons (Hadean, Archean, Proterozoic, Phanerozoic), the three eras of the Phanerozoic (Paleozoic, Mesozoic, Cenozoic) and its twelve periods, from the Cambrian to the Quaternary. Earth forms at the top and today is at the bottom.
- Events. Labels mark when major forms of life first appeared: the first microbes, oxygen in the air, cells with a nucleus, the Cambrian burst of animals, fish, land plants, reptiles, dinosaurs, mammals, birds, flowering plants and finally humans. Tap one to jump to it.
- Even scale or zoom to recent. On the even scale every million years gets the same height, so the whole of animal life squeezes into the bottom eighth. Zoom to recent uses a log scale so the last few million years get room too.
- One year or one day. The sentence under the age says where that moment would fall if Earth’s history were one 365-day year from 1 January to midnight on 31 December, or one 24-hour day.
This fits Class 12 Biology: evolution (origin of life, the history of life, geological time). See how one population changes over generations in natural selection, how rock ages are measured in the radiometric age calculator, and how layers of rock pile up over time in the stratigraphic column maker.
How to use it
- Move the Age slider, or tap an event label on the drawing.
- Read the eon, era and period the age falls in, and how much of Earth’s history had passed.
- Switch As one year or As one day to change the comparison.
- Switch Zoom to recent to see the last few million years clearly.
- Try the Check yourself questions.
Worked example
The first dinosaurs appeared about 233 million years ago. 233 ÷ 4540 × 365 = 18.7 days before the end of the year, which is 13 December at about 06:25. That is in the Triassic period of the Mesozoic era, with 94.9 % of Earth’s history already passed.
The dinosaurs (apart from birds) died out 66 million years ago: 26 December at 16:39, 5.3 days before the year ends. Modern humans, about 300 000 years ago (0.3 Ma), arrive on 31 December at 23:25, only 35 minutes before midnight. On a one-day clock, modern humans turn up at 23:59:54, under 6 seconds before midnight, and the first dinosaurs at 22:46.
Tips
- The Cambrian burst of animal life is not until 18 November. For most of the year, life is only microbes.
- A boundary age belongs to the older span: 66 Ma is counted as the last moment of the Cretaceous.
- The Hadean and Archean have no eras or periods in this simple scale, and the Proterozoic’s eras are left out to keep the drawing readable.
FAQ
Why are the ages rounded? Boundaries are dated from rocks and fossils and are revised as dating improves. Rounded figures are what school books use and are close enough to compare events.
Is the “one year” a real calendar? It is an ordinary 365-day year with no leap day. Each day stands for about 12.4 million years, each hour for about 518 000 years.
Why does the calendar date for an event differ slightly between books? Books use different ages for Earth (4.5 or 4.6 billion years) and for the events, so the dates shift by a day or so.
Where the numbers come from
- Eon, era and period boundaries are rounded from the International Commission on Stratigraphy's chronostratigraphic chart (public scientific dates, rounded to whole millions of years, 2.6 Ma for the Quaternary).
- Event ages are widely quoted round figures from general biology and geology teaching; scientists' estimates vary, especially for the oldest events. The calendar and clock comparisons are fibub's own arithmetic (age ÷ 4540 Ma × 365 days or 86 400 s). Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.