TECHNOLOGY

Counting Atoms to Tell Time

1949 CE

Phanerozoic · Cenozoic · Quaternary · Holocene · Meghalayan

Living things take in a radioactive form of carbon while they breathe and stop at death, after which it decays at a fixed rate. What is left measures the time since. The method was first tried on wood whose age was already known from written history, including Egyptian pieces, because a clock is only worth having once it has been checked against something.

Why it matters

Archaeology stopped arguing about which site came before which and started giving dates. Every age on this timeline under fifty thousand years rests on it, and the fifty thousand is the method's own limit: past that, too little of the carbon is left to count, which is why everything older here is dated by other clocks.

Dating & uncertainty

The method was validated against objects of known age, including Egyptian wood, before being trusted on unknowns. It reaches back about fifty thousand years, which is why everything older on this timeline is dated by other clocks.

Sources

1. Arnold & Libby (1949), Science · Age determinations by radiocarbon content: checks with samples of known age
2. Currie (2004), Journal of Research of the National Institute of Standards and Technology · The remarkable metrological history of radiocarbon dating

Earth history as one day

23:59:59.99851.5 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day