Denis-Didier Rousseau
In search of the stone snails
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Denis-Didier Rousseau. Click here for a larger image.
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Yes, he really does still exist: the travelling researcher tracing the tracks of Humboldt around the world and feeling at home wherever he happens to pitch his tent. French palaeontologist Denis-Didier Rousseau gives an account of his work.
A Europe growing together is asking itself how scientists can be given a helping hand. Mobility is a hot issue nowadays. And yet a glance at the lives of Alexander von Humboldt and many other leading lights in sciences in the past shows that researchers have in fact always been mobile. Indeed, the work of a natural researcher would be inconceivable without mobility. A palaeontologist in particular has hardly any other option but to seek his object of research on location. This is also the case because, often enough, fossils can only be properly classified and will only reveal their secrets to their discoverer in their immediate environment.
So since I completed my doctorate, I have constantly been travelling around in several regions and countries. My speciality is fossil communities of terrestrial molluscs. Or to put things in simpler terms, snails that lived 2.5 million years ago. Admittedly, these aren't especially spectacular creatures. And of course they attract far less media attention than the famous dinosaurs or fossil hominids. However, they enable the development of a very true-to-live replica of the fossil environments which reflect climate change on Earth. They occur in large numbers in loess, a sediment transported by wind that serves as a palaeontological and palaeoclimatical archive. Today, there are only a handful of experts in this area throughout the world, which makes exchanging information among colleagues rather difficult. On the other hand, one is free to seek one's location of assignment without having to worry about any rivals. Whether it is Europe, China or the USA - you go wherever the snails happen to be.
Hanging from a rope to work
Usually, the regions are easily accessible, whereas the fossils are not. Intensive preparations are required to gain 15 kilogrammes of material from a sediment with a thickness of ten centimetres. In an outcrop area of about ten square metres, the sediment is removed by hand down to a depth of half a metre. Machines would destroy the image of the geological layers. This is why we use spatulas or tools we have made ourselves. Often, the walls we examine are dead vertical, and we work with ropes just like mountaineers.
Thus, the cuts of the spatula eventually add up to tons of sediments. But all this still hasn't exposed a single snail's shell. In the wide expanses of the American prairies or Chinese gullies, this results in a big problem. For often, there are no water sources near the research location to clean the sediment samples. But they have to be cleaned on site, for bringing all the samples to a laboratory in order to prepare them there would cost a fortune. So all what is needed is a fine sieve and - lots of water. In the USA,my colleague and I were lucky enough for the owner of the land we were working on to regularly fill up a pool that had served as a water trough for cows many years ago. Thus it took us a whole week bending over a cattle trough to wash our samples in a few cubic metres of water somewhere in deepest Nebraska. The locals were asking themselves what these two Frenchmen were doing in such a remote place!
Five tons on our backs
In China, however, we had to build our own little basin that really did hold several cubic metres of water but had to be emptied each night to prevent the plastic cover on it from being stolen.Here, we are examining deposits of sediment that is 132 metres deep in total. So far, we have managed a mere 35 metres from the top yielding the younger mollusc assemblages from the last 470,000 years.We have probably carried about 5.25 tons of sediment on our backs up to the place where we collect it. The physical effort is accompanied by other inconveniencies such as snakes, poisonous plants, the danger of dehydration and landslides. You have to put up with a lot, but nobody will notice this when reading about the results published in an international specialist journal.
However, working in a natural environment makes up for almost everything else. Each time I arrive at Luochuan in Central China, I feel like the master of my own garden. As a research wanderer, I get to know other people, cultures and landscapes. This is a personal enrichment I would not like to miss for anything in the world and that teaches me to stay humble in my work and put the little problems at the laboratory or in everyday life into perspective. And what could be more pleasant than to link up the beauty of the landscapes with the work on site and encounters with other societies - and, with all due modesty, to wander in the tracks of researchers like Alexander von Humboldt.
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