1000 years squeezed into 30 centimetres! Precisely such rich historical archives have been drilled from the seabed in the Cariaco basin off the Venezuelan coast in the form of sediment samples as part of an ocean-drilling programme (1). This archive, however, it only useful if its content can be read. Now, ETH researchers working with the geologist, Gerald Haug, and the chemist, Detlef Günther (2) have found a key to open up the archives of climatological history with a resolution which makes it possible to date events to the exactitude of two months. The analysis of an extract from the years 700 to 1000 has led a great revelation, which has ripped through the world's scientific press. In the years 810, 860 and 910 the region suffered three great droughts, dates which exactly coincide with the times that archaeologists believe signalled the collapse of classical Mayan civilisation.

A scientific riposte

"It's clear to me that droughts were the decisive factor in the disappearance the Maya", says Günther. In his study, jointly published with colleagues in the scientific magazine "Science" (3), he shows that precipitation in the years between 550 and 760 were relatively high with seasonal variations. This time-span coincides with the classical period of the Maya when this civilisation was at its height. After 760 the climate became dryer with three great droughts following in 50-year cycles. This strongly suggests that the Maya population increased until 760, perhaps to the limit of what the environment could support. In the event, a sophisticated water supply system was insufficient to ensure survival in a climate that was becoming drier and drier.

The objection, raised in the "New Scientist" by an archaeologist, that Mayan civilisation reached its peak in the driest region of the empire does not disconcert Günther. On the contrary, it confirms his findings; "the drought in the drier regions was doubly fatal for the Mayan population." He received a lot of reactions to the article. The majority is relieved that scientific investigation has put an end to endless speculation. For Günther himself, coming from chemistry, and not accustomed to the plethora of theories which presents itself to archaeologists, it is clear that the defenders of other theories now have to find equally convincing or even better scientific evidence if they want to dismiss climate as the most determinant factor in explaining the disappearance of Mayan civilisation.

The X-ray fluorescence spectrometer (left) used to examine sediment samples in a sample chamber (right). This allows researchers to analyse one metre long drilled core sections (picture by Markus Küpfer). large

Micro X-ray fluorescence made it all possible. Already when deciding on his new X-ray fluorescence spectrometer, Günther was careful to choose an instrument that could deliver high resolution and non-destructive analyses. He turned his attention to archaeological questions and the examination of colour composition of paintings for an application. Why not use the machine to investigate climate? Günther worked out how long an entire analysis of sediment samples would take-and hesitated. It would mean that the machine would be in use, and thus unavailable for other work for days on end, examining sections that would provide certain testimony. In the end he decided to run a test-with success! Samples were examined using a 50-micrometer resolution, a resolution that corresponds to a time period of two months.

"Instrument will not need to be advertised"

For the test it did not matter to Günther what time period he examined but following the successful test the researchers involved chose a specific section drilled from the core, which corresponds to the period of decline of Mayan civilisation. In addition, and with the help of Markus Küpfer from the chemistry workshop, a new sample chamber was constructed for the Micro-Eagle II so that researchers could examine core pieces of up to 1.1 meter in length without breaking them. "The method and the machine will quickly catch on, even without advertising", prophesies Günther. For the first time climatologists have a reliable way to pinpoint time. Günther is not planning to become a climatologist himself. It is his job to further develop, improve and validate the method. He lets is be understood that he does not stand at the beginning of this endeavour. Listening to him, one cannot dismiss the suspicion that Günther has a further methodological surprise in the pipeline.