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Radio Carbon Dating

By: Grahame Johnston - Updated: 19 Jan 2017 | comments*Discuss
 
Radiocarbon Dating Archaeological

The most important archaeological dating method is radiocarbon dating. It is a technique that can yield absolute dates with accuracy up to approximately 5000 years before present. However its application has caused extreme confusion and misunderstanding of the archaeological record. Knowing the limitations of this dating method can help avoid colossal archaeological misinterpretations that would otherwise distort history.

Carbon Everywhere

Radiocarbon or C14 dating employs complex systems of measuring the unstable isotopes in once living matter. There are three forms of carbon that naturally occur forming the building blocks of all plant and animal life. The stable C12 and C13, and the unstable or radioactive Carbon 14. C14 is found in very low quantities in nature. Only one C14 atom exists for every one trillion C12 atoms.

Creating C14 Atoms

Nitrogen atoms in the upper atmosphere are struck by cosmic radiation and create C14 atoms. These atoms rapidly decay into radiocarbon-dioxide and along with ordinary CO2 are absorbed by living plants. As plants enter the human and animal food chains the C14 dioxide enters their living tissue.

The Dying C14 Atom

As with any radioactive particle it decays over time. Experiments, first conducted by Dr Willard F. Libby in 1948 at the University of Chicago, showed that C14, tested in his laboratory, decayed at the rate that, projected out, would cause half of its weight to be lost in 5568 years. Hence, the term ‘half-life’ was given to radioactive substances.

The radiocarbon method measures the rate of decay in the C14 of organic matter therefore estimating how long ago death occurred. Archaeologists can use this method to date bone, teeth, plants, seeds, burned food remains, coprolites, wood, and any artefact that contains organic materials such as an iron axe head (iron cannot be tested using C14) with a wooden handle or a bronze spear with a wooden shaft.

Problems with C14 Dating

For radiocarbon dating to be reliable scientists need to make a number of vital assumptions. Firstly, Dr Libby assumed that C14 decays at a constant rate. However, experimental evidence indicates that C14 decay is slowing down and that millennia ago it decayed much faster than is observed today.

Secondly, the theory behind C14 dating demands that there is the same rate of cosmic production of radioactive isotopes throughout time. The industrial revolution has belched hundreds of thousands of tons of carbon gases into the atmosphere increasing the C12 ratio and atomic weapons testing have increased neutron levels.

Thirdly, the environment in which the artefact lies heavily impacts on the rate of decay. For example, C14 leaches at an accelerated rate from organic material saturated in water, especially saline water.

Fourthly, for C14 to test accurately the artefact must have been protected from contamination. Organic matter, being porous, can easily be contaminated by organic carbon in groundwater. This increases the C12 content and interferes with the carbon ratio.

Archaeologists are Concerned

The unreliability of carbon 14 date testing is a great concern to honest archaeologists. They get particularly concerned when C14 testing shows obviously inaccurate results and they are left in uncertainty about the reliability of the dates that they have previously never questioned.

New or Old?

Some examples of abnormal C14 results include testing of recently harvested, live mollusc shells from the Hawaiian coast that showed that they had died 2000 years ago and snail shells just killed in Nevada, USA, dated in at 27,000 years old. A freshly killed seal at McMurdo Sound, Antarctica, yielded a death age of 1300 years ago.

A petrified miner’s hat and wooden fence posts were unearthed from an abandoned 19th century gold hunter’s town in Australia’s outback. Results from radiocarbon dating said that they were 6000 years old.

More Evidence Needed

These anomalies have driven archaeologists to question their earlier conclusions about archaeological sites and their respective civilizations founded on artefact dating. Many theories about societies and their cultures have been based solely on C14 dating results. The honest archaeologist can no longer propose theories and ideas without bringing a wider plate of evidences to the history table.

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[Add a Comment]
Can we know the life ofgold or gold ornanamentsdy carbon dating ?
Honey - 19-Jan-17 @ 2:52 AM
Hi there, I was hoping you could answer a few questions. I've been looking around but I couldn't really find direct answers.. 1. Does artificial radiation affect the results of any absolute dating? 1a. When artificial radiation hits (or gets absorbed by) a dead organic material. 1b. When artificial radiation hits (or gets absorbed by) an inorganic material. 1c. When the organic being was still alive and it absorbed a large amount of radiation. 2. If any of the above is a yes, can artificial radiation still be absorbed below ground? Like for artefacts/fossils. Can they absorb radiation whilst still buried? 3. If #2 is a Yes, how deep can radiation pass through ground? Thank you very much for taking the time to answer my questions!
Mrs. Grey-Darcy - 29-Oct-16 @ 4:40 PM
Riaz - Your Question:
Any radio carbon testing labs in the uk?

Our Response:
A search on "radiocarbon dating labs" on a UK search engine brings up lots of places (mostly universities/research institutions).
ArchaeologyExpert - 18-May-16 @ 11:12 AM
Any radio carbon testing labs in the uk?
Riaz - 15-May-16 @ 6:30 PM
Hi Intrigued, What Science Is and How It Works p291 By Gregory N. Derry Or an peer reviewed university study of this subject. It is now almost universally accepted that C14 decay slows down like water leaking from a hole in a barrel. Conversely, C24 decayed FASTER when the subject host first died.
Expert - 1-Apr-16 @ 7:19 AM
"Dr Libby assumed that C14 decays at a constant rate. However, experimental evidence indicates that C14 decay is slowing down and that millennia ago it decayed much faster than is observed today." I would be very interested in examining this experimental evidence. Please supply the necessary link
Intrigued - 24-Mar-16 @ 12:03 PM
I have a quantity of bog oak from a peat hag in NE Scotland. Unfortunately the Dendrochronological data does not back very far and would like to know if it's possible to get a Radio Carbon Date for this material. If possible can you give me a price and time scale if it can be done.
Glenisla Ghillie - 16-Jul-15 @ 5:35 PM
The British hallmarking system has been around for hundreds of years and includes a date that will tell you how old a piece of gold jewellery is.
ArchaeologyExpert - 9-Jul-14 @ 2:25 PM
i have a friend that askme its is posible to test the date of a gold piece?
athor - 8-Jul-14 @ 4:19 PM
I have two pieces of timber, found in the wild on the west coast of Scotland I am interested to know when the trees lived, can you sample them for me and what cost might it be?
dv - 2-Dec-12 @ 3:54 PM
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