Thanks to fossil fuel emissions, though, the method used to date these famous artifacts may be in for a change.
The burning of fossil fuels is altering the ratio of carbon in the atmosphere, which may cause objects tested in the coming decades to seem hundreds or thousands of years older than they actually are, according a study published in the Proceedings of the National Academy of Sciences.
But Heather Graven, a lecturer in climate physics and Earth observation at Imperial College London, reports in the US journal Proceedings of the National Academy of Sciences that by 2020, as the fossil fuel emissions mount up, the fraction of carbon-14 in the atmosphere could drop to such a level that carbon-dating could become increasingly uncertain.
Fossil fuels are reservoirs of carbon from plants and algae that died so long ago that all the carbon-14 has decayed.
Radiocarbon dating is a 70-year-old technique now used with increasing precision to date anything once alive from the last 50,000 years.
It exploits the natural ratio of two isotopes of carbon in the atmosphere.
That is because the swelling volume of carbon pumped into the atmosphere from factory and power station chimneys and motor and airline exhausts is beginning to artificially “age” the planet’s atmosphere and bedevil attempts to use the technology known as carbon dating.
If emissions continue under the now-notorious “business as usual” scenario, then by 2050 a brand-new cotton shirt will have the same radiocarbon-dating age as the cloak worn by William the Conqueror when he invaded Britain in 1066.
Plants, and the animals that eat them, absorb radioactive carbon-14 and stable carbon-12 from the atmosphere in proportions which – except during the atmospheric nuclear weapons tests in the 1950s and 1960s − have not changed much from the Ice Ages to the beginning of the Industrial Revolution.
When the tree dies or the animal becomes old bones, the carbon-14 decays at a predictable rate, and the ratio that remains in the laboratory sample is a measure of the specimen’s age.
In short, future human emissions may alter one of the most reliable methods for learning about the past.