Relative dating techniques archaeology

There are two techniques for dating in archaeological sites: relative and absolute dating.

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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.

After an organism dies, the radiocarbon decreases through a regular pattern of decay. The time taken for half of the atoms of a radioactive isotope to decay in Carbon-14’s case is about 5730 years.

Half-lives vary according to the isotope, for example, Uranium-238 has a half-life of 4500 million years where as Nitrogen-17 has a half-life of 4.173 seconds!

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.

The extra neutrons in Carbon-14’s case make it radioactive (thus the term, radiocarbon).

Radiocarbon is produced in the upper atmosphere after Nitrogen-14 isotopes have been impacted by cosmic radiation.

Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.

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