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
Carbon dating works by measuring the difference in carbon-12 and carbon-14. When something dies it stops taking in carbon-14.
We know how long carbon-14 takes to break down; so by measuring the difference we know how long ago something died
Carbon dating can’t help us determine diet*; but jaw and tooth remains can. Primarily carnivores will have different observable differences than primarily herbivores in the build of the jaw and wear patterns of the teeth…..we can then study other artifacts like books/songs/paintings/animal bones to see what the likely diet was at the time
*other analysis of isotopes in the bones can help narrow down diet; certain grains will leave markers and seafood vs land protein also have different markers
For carbon dating they use radiation. Us living things have a special form of carbon (the element) know as carbon-14 it will decay over time. By measuring how much of the carbon-14 there is and how much of the normal carbon (carbon-12) there is we can find how long ago it was alive.
To add a bit more precision to what other said. Radiation from space hit the atmosphere of earth and create Carbon 14, while most of the carbon in the atmosphere is carbon 12. Plants use that CO2 to build their body (herbivore eat plant and carnivore eat herbivore) and so you find the same ratio of Carbon 14 to Carbon 12 in the atoms of the body of any living being as you would find in the atmosphere.
Over long period of time, the Carbon 14 in the atmosphere keep getting replenish (that said the exact amount will vary throughout history), but once a living being die it no longer add new carbon to their body. The amount of carbon 12 remain the same because it is stable, but carbon 14 slowly decrease in number as it radiate away.
Knowing how fast carbon 14 decay and by measuring the current ratio of carbon 14 to carbon 12, we can calculate how long it took since the decay started, aka how long since that living being died.
This only work for organic material up to about 50-60,000 years. The reason is that carbon 14 have an half life of 5,730 years. Meaning that after 50-60 thousand years, the amount of carbon 14 decrease by half 8 to 10 times. The amount left is so small by that point that the measurement become meaningless and can’t be relied upon.
Another important aspect is that the amount of Carbon 14 in the atmosphere wasn’t always the same throughout history. A calibration need to be done to adjust the amount of time to represent more accurately the real number. Usually when people publish that kind of data, they give both the uncalibrated and calibrated data, that way as we improve our calibration methods we can go back and improve the data from past work.
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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