For archaeologists, the C-14 method, is a fascinating thing. Although there are now other methods to determine the age of finds. But still, the radiocarbon method, for the development of the inventor, Willard Libby, in 1960, was awarded the Nobel prize for chemistry, the standard procedure in determining the age of organic substances.

Two speleothems from a cave in China is expected to the radiocarbon-help Dating now to more precision. An international team of researchers, certain with the help of the stalagmites in particular detail, such as the concentration of the carbon isotope C-14 in the atmosphere in the past of 54,000 years.

This is a prerequisite to determine the C14 Dating method the age of organic Material such as bone or plant debris correctly. The researchers present their work in the journal “Science”.

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Christian Hamann from the Leibniz laboratory for age determination and isotope research in Kiel, which was not involved in the study, is impressed by the extensive record, the Chinese researchers to Hai-Cheng from the stalagmites have won. Particularly, the age of objects Dating back to the period of 30,000 to 50,000 years ago could be determined more precisely.

The basis of the radiocarbon Dating the radioactive decay of the carbon isotope C-14 is. It is produced in the atmosphere by cosmic radiation and enters in plants, animals and people. A living being dies, it takes in no new C-14. Over the years, the amount of C-14 decreases then more and more, and in 5730 years half. You know the amount of C-14 in a piece, so conclusions as to his age.

It is not a challenge in the case of radiocarbon Dating, the C-14 concentration in the atmosphere over the past thousands of years was constant. To Not have In other words: at any time in the past 50,000 years of the living being stored in the same C-14. A reliable age determination on the basis of the C-14 decay must, therefore, be the temporal Changes of the C-14 concentration in the atmosphere.

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so Far, researchers have managed, for example with old trees. On their rings it is possible to accurately determine how old a certain layer of wood. The C-14 concentration in the different layers of wood is known, we can conclude that the C-14 has changed in concentration over the millennia in the atmosphere. With trees, the time to be up in front of almost 14,000 years ago in bits and pieces to understand.

With the drip-stones, the researchers go to Hai-Cheng from the Institute of global climate change at the Chinese Xi’an Jiatong University in a different way. The stalagmites were grown in a cave in the Chinese province of Jiangsu over the millennia, from bottom to top, by from the ceiling, water dripped and minerals was deposited. The lower part of the drip-stone is older and contains less C-14 Isotope, the tip of the drip-stone is younger and contains more C-14.

The scientists Hai Cheng could set the course of the C-14 concentration within the drip stone in a temporal context, because they are made at the same time so-called uranium-Thorium Dating of the stalagmites. This kind of Dating has the advantage that it is changes in the atmosphere regardless. In the case of plants and animals, however, it is not applicable, because they do not contain uranium isotopes.

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Hamann from the Leibniz-laboratory stresses in particular that there is now for the first time, a coherent data set for the C-14 concentration for the last of 54,000 years. He assumes that the data are incorporated in the new calibration curve Intcal19, whose establishment is expected in the coming year. Calibration curves are used to take account of the fluctuations in atmospheric C-14 concentration over the millennia, in the case of the C-14 Dating.

The results of Hai and his colleagues are not only of importance for the radiocarbon method, but also for the study of the carbon cycle of the earth. Thus, variations of the C-14 concentration in the atmosphere to draw conclusions on Changes in the magnetic field of the earth and also climate-related Changes in the carbon cycle of the oceans.

joe/dpa

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