The Geologist's Dream

A back-of-the-envelope number for what "deep time" actually means.

The earth is, on the standard reading, about \(4.54 \times 10^9\) years old. That’s the number, but the number doesn’t help — your eye sees “\(10^9\)“ and slides off it, the way the eye slides off “billion” in a newspaper. The arithmetic doesn’t take.

Here is one way to make it take.

A second per year

Suppose you sat down and counted aloud, one number per second, no sleep, no breaks. You started at one, and you counted toward the age of the earth.

A minute would take you to 60.

An hour would take you to 3,600 — well before the founding of any city.

A day would take you to 86,400 — past every dynasty that has ever written its name in ink, but only barely.

A year would take you to roughly \(3.15 \times 10^7\) — about thirty million. Around the date when the first apes appear in the fossil record.

Counting one number per second, day and night, you would have to keep counting for about 144 years to reach the age of the earth.

\[\frac{4.54 \times 10^9 \;\text{seconds}}{3.15 \times 10^7 \;\text{seconds per year}} \approx 144 \;\text{years}.\]

What that means

It means that the age of the earth is not large in the way “a million” is large. It is large in the way that if every human born since the American Revolution had spent their entire life doing nothing but counting, we still wouldn’t have finished.

It is large in a way that does not fit in a sentence.

You can sit with this for a while before it gets uncomfortable.

The discomfort is part of the point. Deep time is not a fact about the world that you are supposed to absorb into your everyday life — it is a frame that, briefly, holds you. Then you go back to the day.