Archeology and carbon dating bone dating techniques

Given relatively pristine circumstances, a radiocarbon lab can measure the amount of radiocarbon accurately in a dead organism for as long as 50,000 years ago; after that, there's not enough C14 left to measure. Carbon in the atmosphere fluctuates with the strength of earth's magnetic field and solar activity.You have to know what the atmospheric carbon level (the radiocarbon 'reservoir') was like at the time of an organism's death, in order to be able to calculate how much time has passed since the organism died.

Shells of known age collected prior to nuclear testing have also been dated ( to ascertain the effects of old carbon (i.e., local marine reservoir effects). However, the most common materials dated by archaeologists are wood charcoal, shell, and bone. In brief, radiocarbon dating measures the amount of radioactive carbon 14 (14C) in a sample.

Radiocarbon analyses are carried out at specialized laboratories around the world (see a list of labs at: When a biological organism dies, the radioactive carbon in its body begins to break down or decay.

What you need is a ruler, a reliable map to the reservoir: in other words, an organic set of objects that you can securely pin a date on, measure its C14 content and thus establish the baseline reservoir in a given year.

Fortunately, we do have an organic object that tracks carbon in the atmosphere on a yearly basis: tree rings.

Alone, or in concert, these factors can lead to inaccuracies and misinterpretations by archaeologists without proper investigation of the potential problems associated with sampling and dating.

To help resolve these issues, radiocarbon laboratories have conducted inter-laboratory comparison exercises (see for example, the August 2003 special issue of Radiocarbon), devised rigorous pretreatment procedures to remove any carbon-containing compounds unrelated to the actual sample being dated, and developed calibration methods for terrestrial and marine carbon. Radiocarbon dating can be used on either organic or inorganic carbonate materials.

This process of decay occurs at a regular rate and can be measured.

By comparing the amount of carbon 14 remaining in a sample with a modern standard, we can determine when the organism died, as for example, when a shellfish was collected or a tree cut down.

Trees maintain carbon 14 equilibrium in their growth rings—and trees produce a ring for every year they are alive.

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