The bottom of Turkey’s Lake Van is covered by a layer of mud several hundreds of metres deep. For climatologists this unprepossessing slime is worth its weight in gold: summer by summer pollen has been deposited from times long past. From it they can detect right down to a specific year what climatic conditions prevailed at the time of the Neanderthals, for example. These archives may go back as much as half a million years. An international team of researchers headed by the University of Bonn now wants to tap this treasure. Preliminary investigations have been a complete success: the researchers were able to prove that the climate has occasionally changed quite suddenly – sometimes within ten or twenty years.