Major dating methods used by archaeologists
The C-14 within an organism is continually decaying into stable carbon isotopes, but since the organism is absorbing more C-14 during its life, the ratio of C-14 to C-12 remains about the same as the ratio in the atmosphere.When the organism dies, the ratio of C-14 within its carcass begins to gradually decrease.Potassium-40 is an isotope with a half-life of 1.28 billion years that decays into argon-40.Traditionally scientists compared the ratio of argon and potassium but samples had to be split to measure each, increasing the chance of an error.Depending on the isotope, this can range from milliseconds to billions of years.
When the uranium decays it shoots off particles that punch a hole of sorts in the zircon and leave a small trail. Libby in 1949, and has become an indispensable part of the archaeologist's tool kit since.As the Earth's upper atmosphere is bombarded by cosmic radiation, atmospheric nitrogen is broken down into an unstable isotope of carbon - carbon 14 (C-14).Acheulean stone tools, named after the site of St Acheul in France where they were first found, became finer and more sophisticated over time.These tools range from 1.75 million years old (far left) to 0.85 million years old (far right).
Animals eating those plants in turn absorb Carbon-14 as well as the stable isotopes.