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This image shows a cross section through the earthís crust and upper mantle showing lithosphere plates (made of the crust layer and the top part of the mantle) moving over the asthenosphere (upper mantle).
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Old Rocks Give New Clues about Ancient Earth!
News story originally written on July 11, 2002

What was the Earth like a long time ago? To answer this question, some scientists look for very old rocks to find clues. Now they have found rocks in China that are 2.5 billion year old and these rocks have some interesting clues!

These rocks formed during the Archean Age, when the Earth was young. During the Archean there was no ocean and no continents on the Earth. It was a very hot place. After a long time, Earth cooled a bit, and giant plates of rock started to move around the surface of the Earth just like they do today. This is called plate tectonics . Today, plate tectonics is a very important process on Earth. It makes mountains grow high, volcanoes spew lava, and earthquakes rumble.

Scientists want to know when the Earth was cool enough for plate tectonics to begin. They thought that plates started to move about 2 billion years ago. They thought the Earth was too hot for plate tectonics before that time. But the 2.5 billion year old rocks found in China tell a different story.

These rocks formed in the upper part of the mantle layer, underneath a seafloor. They show that a long time ago they used to flow slowly and were able to move the plates of the Earthís crust that were above them. So, the plates were sliding around long before we thought they could!


Last modified August 6, 2002 by Lisa Gardiner.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA