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Big Machine Reveals Small Worlds
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Results of GSAT are in schools this week
2014 GSAT Results for Jamaican Kids
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Science loses out when ice caps melt
The Rise of Yellowstone
In Antarctica watch the heat (and your step)
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A Vulture's Hidden Enemy
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Chicken of the Sea
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The Surprising Meaning and Benefits of Nursery Rhymes
Expert report highlights the importance to parents of reading to children!
Choosing a Preschool: What to Consider
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Electric Backpack
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Thinner Air, Less Splatter
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Roving the Red Planet
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The Parts of Speech
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Robots on the Road, Again
Ready, unplug, drive
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Weather
The solar system's biggest junkyard
Recipe for a Hurricane
Earth's Poles in Peril
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Earth Rocks On

Most of the time, the ground feels solid beneath our feet. That's comforting. But it's also misleading because there's actually a lot going on underground. Masses of land (called plates) slip, slide, and bump against each other, slowly changing the shape of continents and oceans over millions and billions of years. Scientists know that Earth formed about 4.5 billion years ago. They also know that our planet was hot at first. As it cooled, its outermost layer, called the crust, eventually formed moving plates. Exactly when this shift happened, however, is an open question. Now, an international group of researchers has an answer. They've found new evidence suggesting that Earth's crust started shifting at least 3.8 billion years ago. The new estimate is 1.3 billion years earlier than previous ones. Not long before 3.8 billion years ago, lots of asteroids were pummeling Earth, keeping its crust in a hot, molten state. After the hard crust formed, much of it sank at various times into the planet's hot insides. There, it melted before returning to the surface as lava. In some places, however, the crust never sank. One of the oldest such places is in Greenland, in an area called the Isua supracrustal belt. The rocky crust there is between 3.7 and 3.8 billion years old. The belt was once part of the seafloor, but now it is exposed to air. The researchers recently took a close look at the Isua supracrustal belt. They noticed long, parallel cracks in the rock that have been filled in with a type of volcanic rock. To explain this structure, the scientists propose that tension in the crust caused the seafloor to crack open long ago. Hot, liquid rock, called magma, oozed up from deep inside Earth to fill the cracks. Finally, the whole area cooled, forming what we see today. That explanation, plus chemical clues inside the rock, suggests that the Isua supracrustal belt was once part of a plate under the ocean, beginning around 3.8 billion years ago. "It's a marvelous case of solving a jigsaw puzzle," says one of the researchers, Gustaf Arrhenius of the Scripps Institution of Oceanography in La Jolla, Calif. He notes that the puzzle was "a very difficult one because these rocks are all very old and have been badly mangled."E. Sohn

Earth Rocks On
Earth Rocks On








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