( this region over the past 400000 year...)Scientists find fossil proof of Egypt's ancient climate

The researchers noted that the silt thickness at the lake exceeds five yards, an indication that the humid phase lasted at least several thousand years. Normal rainfall in the area they study is a minuscule 0.7 of a millimeter per year, but there is evidence that the rainfall amounts in the region have gotten up to as much as 600 millimeters per year, "not enough to make it a paradise," Smith said, "but enough to turn a barren environment into a classic savannah."

Kieniewicz performed isotopic analyses of about 20 snails, all of them dating to the humid phase, which occurred approximately 130,000 years ago. These particular snails have a life span of between one and two years, and build their shells in a classic spiral with whatever water is available that day. The snails were preserved in calcium carbonate deposits throughout the lake.

"We're using the chemistry of the water over the course of a year or two, as revealed by isotopic analyses and minor element analyses of the snail shells to determine information about the climate then," Kieniewicz said. "The shell is an archive of the snail's life. The analyses give us snapshots of what the conditions were like in that lake basin."

The geochemical analyses confirmed that the water was a stable standing body for many years. "Strong evaporation of the lake, enough to shrink it substantially in volume and make it more saline would have been expected to result in large excursions in d18O and minor element concentrations," Kieniewicz said. "However, throughout the stratigraphy, the d18O values of the silts remain isotopically light and the minor elements do not show intense evaporative trends, suggesting that the lake remained stable and fresh."

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Source:Washington University in St. Louis