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2017-09-22. Scientists Closing in on the Dawn of Plate Tectonics.

posted Sep 26, 2017, 12:51 PM by Alan Gould
By Shannon Hall, Scientific American. For GSS Energy Flow chapter 2. Excerpt: Geologists think early Earth may have looked much like Iceland—where jet-black lava fields extend as far as the eye can see, inky mountainsides rise steeply above the clouds and stark black-sand beaches outline the land. But over time the world gradually became less bleak. Today Earth also harbors light-colored rocks, like the granite that composes Half Dome in Yosemite National Park. But scientists remain uncertain as to when the world started to transition from the one that looked like Iceland to that which we know today. A new study published Thursday in Science suggests the shift transpired more than 3.5 billion years ago. Not only does the finding tell scientists the color of the world’s early beaches, it might help them understand when tectonic plates—the interlocking slabs of crust that fit together like puzzle pieces far beneath our feet—started to wake up and shuffle around. That is because the lighter-colored rocks, known as felsic rocks, are actually dark, or mafic, rocks “reincarnated.” In short, felsic rocks form when mafic ones are pushed deep inside Earth—possibly when one tectonic plate slips under another in a process called subduction. Given that light-colored felsic rocks were abundant billions of years ago, plate tectonics had likely already kicked into action.... https://www.scientificamerican.com/article/scientists-closing-in-on-the-dawn-of-plate-tectonics1/