The true scale of time

How to read Earth history in one year

Earth forms on January 1. The end of December 31 is the present. Every selected event lies between these points in the same proportion. A familiar calendar makes the difference between a billion, a million and a thousand years easier to grasp.

One proportion for every event

The model uses an Earth age of about 4.54 billion years and a standard year of 365 days. To place an event, we divide its age by the planet's age. The result tells us what fraction of the model year remains between that event and the present. We subtract that fraction from the end of December 31. The rule is the same for a glaciation, a fossil and an invention.

One day represents about 12.4 million years; one second corresponds to about 144 years. This is why most of what we learn as the history of civilization clusters at the very end of the year. The roughly 300,000-year history of Homo sapiens occupies approximately the final 35 minutes.

A long year of microscopic life

Early evidence of life in the Dresser Formation is about 3.48 billion years old. In Earth's calendar it falls in northern spring. This records the presence of life at a particular time and place, not the birth of the first cell. Older candidates and their interpretation remain active subjects of research. A precisely placed dot does not remove the limitations of the fossil record.

For an enormous part of the planet's history, life was predominantly microscopic. Atmospheric changes, the development of cells with nuclei and the emergence of multicellularity span long intervals. The Great Oxidation Event describes rising atmospheric oxygen rather than one instant of change. We show such processes as intervals, with separately dated beginnings and endings.

Why zoom into the end of the timeline?

On a phone, hundreds of thousands of years would occupy far less than one pixel if the whole history of Earth fitted on a single screen. The journey therefore moves from the entire year to December, the last day and the final moments. Each zoom states its range. Equal distances within a scene still represent equal durations.

A date in the model is not an anniversary. A card that says December does not mean that the actual event happened in December. It marks the event's position relative to Earth's age. Likewise, a time calculated from an approximate age is not a measurement accurate to the second. We show the real date or age, an explanation and a source alongside the calendar, and describe significant uncertainty separately.

Find these events in Earth's year

These dates come from the same records as the interactive timeline. Open an event to explore its position and explanation.

Explore the whole Earth year Test your intuition in the quiz

Questions about the scale of time

Does Earth's year have 365 or 366 days?+

The model uses a standard year of 365 days. A fixed length keeps all events in the same proportions, regardless of the actual calendar year.

Does a December date mean an event really happened in December?+

No. A date in Earth's year marks an event's position on the scale from the planet's formation to the present. Its actual date or approximate age appears alongside it.

Sources and further reading

Earth in motionContinental driftTurn back time on a map. Explore Pangaea, Rodinia and the earlier history of land.TimeEarth history in one yearPlace life, climate and humans in a calendar spanning 4.54 billion years.QuizTest your sense of timeWhen did it happen if Earth's entire history lasts one year?WaterWater in true scaleCompare oceans, drainage basins, and lakes. Estimate the scale, then check the data.