"Somewhere, something incredible is waiting to be known" Carl Sagan
sábado, 17 de diciembre de 2011
Ancient Environment - A Dry Dead Sea before Biblical Times
The Dead Sea nearly disappeared about 120,000 years ago, say researchers who drilled more than 1,500 feet below one of the deepest parts of the politically contentious body of water.
View of the Dead Sea [David Shankbone.Wikipedia]
The discovery looms large at a time when the Dead Sea is shrinking rapidly, Middle Eastern nations are battling over water rights, and experts hotly debate whether the salt lake could ever dry up completely in the years to come.
New data from drilled deposits are also helping piece together geological history that slices through Biblical times. Further research may offer opportunities to verify whether earthquakes destroyed the cities of Sodom and Gomorrah or if Joseph stockpiled grains in Egypt to weather a real famine.
"We see a lot of these different stories in the Bible about fat years and lean years," said Steven Goldstein, a geochemist at Columbia University in New York. "And we can see in the record that there were these intervals where it looks like it was a land of milk and honey, and there were intervals where there was no water, no rain and I'm sure, famine. Climate validates that there were these rhythms."
The new research started, not as an attempt to investigate Biblical events, but to understand the history of the Dead Sea, which has been drying up at dramatic rates in recent decades. As a result of both evaporation and intensive human demands for water from inflowing rivers, the surface of the lake dropped 23 meters (75 feet) from 1930 to 2000, said Emi Ito, a geochemist at the University of Minnesota, Twin Cities.
And the lake's rate of shrinking seems to be accelerating. From 2000 to 2008, levels dropped 8 m (26 feet), with another 1.5 m (5 feet) lost in 2010 alone.
Even as the lake's salty shores recede, though, scientists have long debated whether it could ever totally dry up. Because the water is so salty and because salt and water molecules attract each other, many modeling studies have suggested that some amount of water will always remain there.
To see if history could help settle that debate and others, an international team of researchers drilled down about 460 m (more than 1,500 feet) into sediments of the Dead Sea in Israeli territory at a spot that was just slightly shallower than the lake's deepest point, which lay on the other side of the border in Jordan. The cores they pulled up stretched back 200,000 years.
At a level corresponding with 120,000 years ago, during a warm period between ice ages, the researchers found a layer of small round pebbles sitting on top of 45 meters (nearly 150 feet) of thick salt deposits. Those pebbles, they announced this week at a meeting of the American Geophysical Union in San Francisco, look just like the rocks that normally appear on the lake's beaches -- suggesting that one of the deepest parts of the lake was once dry.
"It seems as though the lake may have dried out or got very close to drying out without human intervention," Ito said. "We may have to revise our thinking that the Dead Sea cannot dry out."
That very dry period many millennia ago was much hotter than it is today, said Jiwchar Ganor, an environmental geochemist at Ben-Gurion University of the Negev in Israel. Humidity was lower. And there was less water flowing into the lake then there is today.
He doubts the lake actually dried up altogether then -- or that it will disappear completely in the future, even as it keeps shrinking at an alarming rate.
"We can say that even without changing climate, it will continue to drop," Ganor said. "But it will still be at a higher level than what it was in the time they found here."
Still, there's no way to know how modern-day human interventions will interact with future climate change to affect the Dead Sea. And if the Dead Sea could become mostly dry once, the concern is that it could happen again, raising the likelihood for wars over water and the loss of still mostly unstudied life forms that manage to thrive in such saline waters.
Meanwhile, historians and Biblical scholars are watching closely to see what the next stages of research will turn up in the sediments, which reveal details of past climate and earthquakes.
Book XV of the Antiquities of the Jews, for example, describes an earthquake that destroyed Judea and killed 30,000 people. And the Book of Joshua tells of a quake that tumbled the walls of Jericho and stopped the Jordan River from flowing, allowing the Israelites to pass through.
Perhaps the Dead Sea harbors answers to these ancient mysteries.