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uni'wissen 02-2015_ENG

primarily from Northern France and Southern Germany: from the medieval towns, the remains of ancient and prehistoric settlements, trenches from the First World War, gravel pits, or sawmills. His most important tool besides the computer is a microscope. He uses the instrument to count growth rings and measure their width. Damp and mild years lead to wide rings, because favorable weather conditions stimulate tree growth. Dry years, on the other hand, manifest themselves in narrow rings. Other features that provide valuable information include the anatomy and the chemical composition of the wood. Along with climatological data garnered from ice core drilling, growth rings are the richest data source for modern paleo- climatological research. Dendrochronology works with reference chro- nologies compiled over the course of thousands of analyses: taking the present as a starting point, researchers initially study younger wood and then move on to older wood from trees with overlapping life spans. The longest of these growth ring calendars is being done at the University of Hohenheim and currently goes back 12,500 years into the past – to the end of the last ice age, long before humans began to adopt a sedentary lifestyle. “The growth rings of trees are as precise and individual as a barcode,” says Tegel. When was the tree used for the roof beams of a medieval house in the northeastern French town of Troyes chopped down? How many days of sunshine did the oak built into a well pit 7000 years ago near modern-day Leipzig see? How extensive were the climactic fluctuations in the area, and how sudden were these changes? It is essential for climate research to find answers to such ques- tions, because they provide precise information on prehistoric times, of which we have no written records whatsoever. Our body of reliable data from meteorological instruments only covers the past 150 years. Wood built into above-ground structures is decomposed by microorganisms and therefore does not usually last longer than a thousand years. However, much older constructions made of wood have been preserved because they were embedded in a damp environment, such as A map for each year: Willy Tegel has created maps showing climactic conditions over the past 2500 years. In 1315, for instance, large parts of Europe were rainy (green), while 1540 was a dry year (brown). Source: Willy Tegel uni wissen 02 2015 “We are at the interface between the social and natural sciences.” 18 uni wissen 022015