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Science Frontiers ONLINE No. 21: May-Jun 1982 |
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What's ok in the mediterranean is verboten in the atlantic and the pacific
Geologists and geophysicists have now satisfied themselves that a few million years ago the Mediterranean dried up nearly completely. The Deep Sea Drilling Project discovered in 1970 and 1975 that layers of evaporites existed beneath the Mediterranean's floor. In addition, over 80 years ago, the bed of the Rhone River was found to consist of river sands and gravels superimposed upon hundreds of feet of oceanic sediments. Beneath these deposits -- some 3000 feet down -- was a gorge cut in granitic rock. Other rivers emptying into the Mediterranean had cut similar gorges into solid rock long ago. No one could provide an acceptable explanation for the deep-cut gorges until the evaporites proved that the water level had been low enough for the rivers to cut the gorges subaerially. In other words, the Mediterranean's level fell several thousand feet, allowing the rivers to erode gorges much as the Colorado does today in the Grand Canyon.
(Smith, E.G. Walton; "When the Mediterranean Went Dry," Sea Frontiers, 28:66, 1982.) Comment. The Med's buried gorges are obviously close cousins of the many submarine canyons found around the world's continental shelves. Most geologists strongly resist any explanation of the submarine canyons involving subaerial erosion, because no one believes the oceans ever dropped thousands of feet. True, the Med's evaporites confirm a great reduction in water level there, but the flat-topped guyots in the Atlantic and Pacific do the same for the oceans -- or at least seem to. The guyot tops are now thousands of feet below the surface, just like the Mediterranean's evaporites. It is thought-provoking to notice that the Mediterranean (and the oceans?) began to dry up about 5 million years ago, just about when humans are supposed to have split off from the other primates.
Reference. Flat-topped guyots are cataloged at ETH1 in Carolina Bays, Mima Mounds. Description of this book here.