The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / (-0.693) ] x 5,700 years t = [ 3.323 ] x 5,700 years Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old.If this were so, the width of the annual growth rings would show changes in synchronism with the sunspot numbers.
His laboratory is still one of the leading centres in world dendrochronology.
It was not until 1939 that the science was taken seriously in Europe, mainly through the efforts of Professor Huber in Germany, and not until after World War II that such studies became established in the UK.
Upon encountering a new site, the archaeologist immediately requires information about its age in order to set it in context with other sites.
In research into our heritage the conservationist or architect may be able to date the general period of a building he is working with from either the situation, materials of construction, type of timber joints or other stylistic features.
Almost certainly the century or portion of a century when it was built may be assigned with some certainty.
However, as more and more work is done and increasing numbers of structures with complex constructional phases are encountered, the general features may not be sufficient to give the accuracy in dating that is currently required.
These are: dendrochronology (or 'tree-ring' dating), radiocarbon dating and thermoluminescence dating.
Each method has a distinct role in the investigation of historic buildings.
Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).
The use of various radioisotopes allows the dating of biological and geological samples with a high degree of accuracy.
Dendrochronology is the oldest method, having been introduced over a century ago by an American astronomer, Professor A E Douglass.