GENETICS × EVOLUTION

Reading Time in Proteins

1962 to 1965 CE

Phanerozoic · Cenozoic · Quaternary · Holocene · Meghalayan

If mutations accumulate at a roughly steady rate, then the number of differences between two species measures the time since they parted. Molecules became documents of history, readable without a single fossil. Palaeontologists resisted it violently for twenty years, and they were half right: the clock runs at different speeds in different lineages and different genes, and has to be calibrated against fossils to say anything in years.

Why it matters

Half the dates on this timeline before the Cambrian come from clocks like this one. Wherever the fiche you are reading says that the genes and the rocks disagree, this is the method on one side of the disagreement, and its dependence on fossil calibration is why the two are never fully independent.

Dating & uncertainty

The idea was proposed in the early 1960s and violently contested by palaeontologists for two decades. It is now standard, with the important correction that the clock ticks at different rates in different lineages and genes.

Sources

1. Zuckerkandl & Pauling (1965), Journal of Theoretical Biology · Molecules as documents of evolutionary history
2. Kumar (2005), Nature Reviews Genetics · Molecular clocks: four decades of evolution
3. Morgan (1998), Journal of the History of Biology · Emile Zuckerkandl, Linus Pauling, and the molecular evolutionary clock

Earth history as one day

23:59:59.99881.2 ms before midnight

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