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There are two techniques for dating in archaeological sites: relative and absolute dating.
Relative dating stems from the idea that something is younger or older relative to something else.
How It Works: Carbon has 3 isotopic forms: Carbon-12, Carbon-13, and Carbon-14.
The numbers refer to the atomic weight, so Carbon-12 has 6 protons and 6 neutrons, Carbon-13 has 6 protons and 7 neutrons, and Carbon-14 has 6 protons and 8 neutrons.
Limitations and calibration: When Libby was first determining radiocarbon dates, he found that before 1000 BC his dates were earlier than calendar dates.
He had assumed that amounts of Carbon-14 in the atmosphere had remained constant through time.
Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.
So every living thing has a certain amount of radiocarbon within them.
More recently is the radiocarbon date of 1950 AD or before present, BP.
In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
Although relative dating can work well in certain areas, several problems arise.
Long tree-ring sequences have been developed throughout the world and can be used to check and calibrate radiocarbon dates.
An extensive tree-ring sequence from the present to 6700 BC was developed in Arizona using California bristlecone pine (), some of which are 4900 years old, making them the oldest living things on earth.
When it comes to dating archaeological samples, several timescale problems arise.