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Remnants of Earth’s original crust preserve time before plate tectonics

Full-blown plate tectonics had late start, geochemical evidence suggests

2:00pm, March 16, 2017
Oldest rocks yet

CLASSIC ROCK  Rocks from an outcrop in northeastern Canada may have formed from material dating back more than 4.2 billion years ago. That’s older than the oldest rocks found on Earth’s surface today.

Not all of the newborn Earth’s surface has been lost to time. Transformed bits of this rocky material remain embedded in the hearts of continents, new research suggests. These lingering remnants hint that full-fledged plate tectonics, the movements of large plates of Earth’s outer shell, began relatively late in the planet’s history, researchers report in the March 17 Science.

These revelations come from ancient continental rock in Canada that preserves geochemical traces of the even older, 4.2-billion-year-old rock from which it formed. “For the first time, we can say something about what kind of rock was a precursor to the first continental crust,” says study coauthor Jonathan O’Neil, a geochemist at the University of Ottawa.

Earth began as a molten ball around 4.54 billion years ago, and over the next tens of millions of years, its surface cooled

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