The valley is full of deposits of loess, or silt, that has hardened into rock after millions of years of under intense pressure. Loess is commonly created when glaciers grind rocks into powder, and the wind then sweeps the powder into great heaps. Some of the broken-up pieces of rock Soreghan and her team found are also striated, a feature that glaciers often leave as they scrape slowly across the landscape. If Unaweep were carved by a huge tongue of ice in the late Paleozoic, it would have been too low in elevation, perhaps 500 to 1,000 meters (1,640 to 3,280 feet) above sea level. Soreghan suggests we may need to rethink what climate was like back then. "The implication is that the magnitude of climate change between glacial and interglacial periods was either huge, or it just stayed a lot colder all of the time." Soreghan said. But Nick Eyles of the University of Toronto said the evidence isn't conclusive: "These types of deposits can be formed in several different ways. There's an 'if' or a 'but' to every plank of their conclusions." "It's good because it will make people think," he said of the team's work. "But they're arguing for a global climate event from one canyon, and on weak evidence. This is a radical reinterpretation of climate, and that's got to be matched by better data." One way to prove their case, Eyles said, would be if the team went back and found striations raked across the canyon walls, a 'smoking gun' that a glacier carved the ancient Unaweep. Related Links: Discovery News blog: Earth Impacts |
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