"Back then, the Nazca and South American plates were converging at a rate of around 15 centimeters [six inches] per year," Meade said. That is far faster than the rate at which the Indian and Eurasian plate are colliding to form the Himalayas today. "But it was soaking wet," said Meade. "Then all of a sudden there was this aridification." Climate studies of the period show that the Andes region was a rainforest until 15 million years ago. Annual precipitation suddenly dropped from two meters (6.5 feet) to 20 millimeters (0.79 inches), reshaping the landscape into the parched desert it is today. The lack of rain would have greatly reduced erosion, Meade and co-author Clinton Conrad of the University of Hawaii reason, allowing the young, humble Andes to rise to prominence. As the mountains grew so did their weight, and the hefty range pushed down on the Nazca plate until friction slowed convergence to just seven centimeters (2.7 inches) per year, about half of what it was before the rains ceased. "It's this amazing story -- we're at the beginning of understanding how climate affects plate tectonics," Meade said. "This is a very interesting idea for sure, and a very good first step," Lindsay Schoenbohm of The Ohio State University said. On whether human-induced climate change could ever affect tectonics, she said "It's a timescale question. Modern climate change has been going for tens to maybe hundreds of years. The change in climate would have to persist for hundreds of thousands of years at least, so the scale doesn't match up right now." Related Links: Discovery News Blog: Earth Impacts |
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