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 the idea violently for twenty years, and they were half right: the clock runs faster in some lineages and some genes than in others, and it 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 you read here that the genes and the rocks disagree, this is the method on one side of the argument, and its dependence on fossil calibration is why the two are never fully independent.
Dating & uncertainty
The idea was set out in these years; it was not accepted for two decades more. And because a clock must first be calibrated against fossils, every age it returns leans on the fossil record.
Sources
- Zuckerkandl & Pauling (1965), Journal of Theoretical Biology · Molecules as documents of evolutionary history
- Kumar (2005), Nature Reviews Genetics · Molecular clocks: four decades of evolution
- 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
See it on the timeline