Not entirely sure if this falls under the Biology or Chemistry tag but heigh ho!
I am a Viking Reenactor and our group is very education focused and as part of my stall on Viking Funerals I talk about how scientists can test bodies to find out where they’re from and what their diets were like but I don’t actually know “how” this works…
In: Biology
I read archaeology at university and did a whole module on this, hopefully I can spell it out clearly!
First up, quick terminology note! “Forensic” archaeology is archaeology done for court or legal proceedings. Forensic archaeology can use most techniques also used in mainstream archaeology, though radiocarbon dating doesn’t tend to be relevant because there’s usually more precise ways of dating things that recent.
Radiocarbon dating, sometimes shortened to carbon dating, is a form of isotope analysis. Elements are made up of protons and neutrons – the number of protons determines what element it is, while the number of neutrons determines the isotope. For example, ^(1)H (Hydrogen-1, or normal hydrogen) has one proton and no neutrons for an atomic weight of 1; ^(2)H (Hydrogen-2 or Deuterium) has one proton and one neutron for an atomic weight of 2. Most elements have one most stable isotope (eg ^(1)H) and all other isotopes will be unstable and will eventually turn into (decay into) that stable isotope. This decay happens by random chance, but like all things will end up with an average. The amount of time for half the unstable isotope to decay into the stable isotope is called its half-life.
The most common isotope of Carbon is ^(12)C, which is stable. ^(13)C, which is about 1% of all carbon, is also stable, then ^(14)C is extremely rare *but* has a very helpful half-life of around 5,700 years. Many isotopes either have super short half lives (fractions of a second) or very long ones (hundreds of thousands or even millions of years, which can be good for fossils or ancient rock but not so much for most archaeology). ^(14)C is formed in the atmosphere from cosmic rays hitting ^(12)C.
All living beings contain carbon, and that carbon eventually comes from the atmosphere via photosynthesis. So in living beings, the ^(14)C % is about the same as in the atmosphere. When the being dies, however, they can’t take any more in, and it slowly turns to ^(12)C. After 5,700 years, half of it will change, so if archaeologists find that something contains about half the level of ^(14)C in the atmosphere, they would know it’s about 5,700 years old. If something has about a quarter of the level, it’s about 11,400 years old. (Numbers approximate, there are some details.)
(Putting the stuff on diets into another comment.)
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