Radiocarbon dating the iceman

The carbon exchange between atmospheric CO2 and carbonate at the ocean surface is also subject to fractionation. Reservoir Effects Libby’s original exchange reservoir hypothesis assumed that the exchange reservoir is constant all over the world, but it has since been discovered that there are several causes of variation in the 14C/12C ratio across the reservoir. Marine Effect The CO2 in the atmosphere transfers to the ocean by dissolving in the surface water as carbonate and bicarbonate ions; at the same time the carbonate ions in the water are returning to the air as CO2.This exchange process brings14C from the atmosphere into the surface waters of the ocean, but the 14C thus introduced takes a long time to percolate through the entire volume of the ocean. Hard Water Effect If the carbon in freshwater is partly acquired from aged carbon, such as rocks, then the result will be a reduction in the 14C/12C ratio in the water. Volcanoes Volcanic eruptions eject large amounts of carbon into the air.For example, if 1% of the benzene in a modern reference sample is allowed to evaporate, the resulting radiocarbon age will be too young by about 80 years. Limit of Measurability The limit of measurability is approximately eight half-lives, or about 45,000 years.

Since different materials have different δ13C values, it is possible for two samples of different materials, of the same age, to have different levels of radioactivity and different 14C/12C ratios.

To compensate for this, the measurements are converted to the activity, or isotope ratio, that would have been measured if the sample had been made of wood. Systematic Errors It is also possible for laboratories to have systematic errors, caused by weaknesses in their methodologies.

These include the main stable isotope (12C) and an unstable isotope (14C).

Through photosynthesis, plants absorb both forms from carbon dioxide in the atmosphere.

Although Libby had pointed out as early as 1955 the possibility that this assumption was incorrect, it was not until discrepancies began to accumulate between measured ages and known historical dates for artefacts that it became clear that a correction would need to be applied to radiocarbon ages to obtain calendar dates. The uncalibrated, raw BP date underestimates the actual age by 3,000 years at 15000 BP.

The underestimation generally runs about 10% to 20%, with 3% of that underestimation attributable to the use of 5,568 years as the half-life of 14C instead of the more accurate 5,730 years.

Two days after the first discovery, Hans Kammerlander and Reinhold Messner, two famous mountain climbers from South Tyrol happened to arrive at the site, and the photo of figure 1 shows them watching the Iceman.

Messner made a first guess at the age of the man and thought he might have died some 500 years ago.

These records allow fine-tuning, or “calibration”, of the raw radiocarbon age, to give a more accurate estimate of the calendar date of the material.

One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites. Carbon has two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C), and a radioactive isotope, carbon-14 (14C), also known as radiocarbon.

When an organism dies, it contains the standard ratio of 14C to 12C, but as the 14C decays with no possibility of replenishment, the proportion of carbon 14 decreases at a known constant rate.