Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.
Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.
Your T-shirt could soon contain the same carbon-14 as William the Conqueror’s robe from 1066 AD, scientists warn.
An article in Phys Org claims that radiocarbon dating is becoming more unreliable as carbon emissions increase. Fossil fuel emissions could soon make it impossible for radiocarbon dating to distinguish new materials from artefacts that are hundreds of years old. Fossil fuels like coal and oil are so old that they contain no carbon-14.
These are also known as radiocarbon atoms, and they are unstable because they decay (which means they are radioactive) into a different type of atom–nitrogen.
There are many more stable carbon atoms in the atmosphere than unstable ones.
Incidentally, lab techs already have to correct for another historical contingency: The fraction of carbon-14 in the atmosphere decreased after the Industrial Revolution with the rise of fossil fuel combustion.
But in the 1950s and 60s, nuclear weapons testing caused a sharp increase.
It does not work on rock, for example, but does work on wood.
A question I am often asked at seminars relates to the radiocarbon method of dating old things.
People have been told that carbon-14 is a good indicator of an old earth and therefore supports the evolutionary idea. The assumption that carbon dating supports a very old earth is outdated.
Sometimes, archaeologists will date an object by carbon dating another object nearby.
This method of dating obviously relies on assumptions about the relationship between the object and the actual tested material.