Each year, a ring forms under the bark of trees which testifies to their growth during the favorable season, between spring and the end of summer. These rings are so clear – especially in temperate regions of the world where the seasons are well marked – that archaeologists use trunks to date events with unmatched precision, down to the year. Better still, the physico-chemical analysis of the content of each of the rings makes it possible to discover the average climatic conditions which prevailed during its formation.
A team did this on 21 live oaks and 126 old tree samples from an area in the Czech Republic and another nearby area in south-eastern Bavaria. Each tree provided data – year by year – over an average period of about a century (between 80 and 120 years). And because the life spans of these trees overlap, the researchers obtained data from an average of seven different trees in a given year, reducing uncertainties. Their results appeared on March 15 in the journal Geoscience of nature.