Snails reveal human history

Fossils occupy the wet phase in western Egypt 130, 000 years ago

130, 000-year-old fossil snails David Kilper / WUSTL Photo
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Fossil snails have provided scientists with important clues to the climate of the past in northern Africa. The shells of the molluscs revealed that today's desert regions of Egypt must have been a lush savanna landscape with giraffes rhinos and early humans some 130, 000 years ago.

Jennifer R. Smith, assistant professor of geo- and planetary sciences at Washington University in St. Louis, and her colleague Johanna M. Kieniewicz examined fossils of freshwater snails Melanoides tuberculata and carbonate deposits from a small, now dry lake in the Kharga Oasis in western Egypt. Using isotope and elemental analyzes, they reconstruct climatic conditions during the water-rich period of this lake.

"We use the chemistry revealed by isotope analysis of the water stored in their shells by snails in the course of a year or two to obtain information about the climate of the time, " explains Kieniewicz. "The shell witnesses the life of the snail. The analyzes give us snapshots of what the living conditions in the lake basin were like. "

The results gave the surprising picture of fertile and humid Egypt 130, 000 years ago. The geochemical analyzes confirmed that the lake must have been a stable source of water for many years. Kieniewicz: "In the stratigraphy data from the deposits show no intense traces of evaporation, indicating that the lake remained stable and fresh." The scientists also found that the deposits in the lake were more than 4.5 meters thick and occupy that the wet phase must have lasted at least several thousand years.

Evidence of the presence of hominids was also found in the form of Stone Age artifacts such as stone scrapers and blades. They also allow conclusions about the migration behavior of humans during this time and the spread of modern humans from Africa to other continents. display

"The artifacts provide us with evidence that humans came to this lake. Genetic data suggest that 100, 000 to 400, 000 years ago was a critical time for the evolution and spread of African hominids, "explains Smith. "Our climate data from this humid phase 130, 000 years ago suggests that this could have been a particularly good time for a northward migration, always to the reliable watering holes. It was apparently the most stable and strongest humid phase in the region in the last 400, 000 years. "

(Washington University, 09.02.2005 - NPO)