When Slime Ruled: Life Slowed by Earth's Stuck Plates: Page 2

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"This increase in activity could have kick-started a myriad of changes, including changes to levels of key elements in the atmosphere and seas, which in turn may have induced evolutionary changes in the life forms present," Cawood said.

Blame Earth's temperature for the fits and starts in continental speed. According to the study, on the hot, young Earth, continents grew quickly, with about 70 percent of the "scum of the Earth" forming by 3 billion years ago, the researchers said. But the mantle, the hotter layer between the crust and the core, was still too warm for modern plate tectonics to rev up. Big fragments of continents couldn't slide into the mantle at collisions called subduction zones. So when the first supercontinent formed, the plates stuck together in a massive jam for a billion years while the mantle continued to cool off.

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"This represents a unique period of environmental, evolutionary and lithospheric stability," Cawood said.

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DCI

While algae and microbes were whiling away the boring billion, the continents were growing a gut, adding bulk to their bottom layer as the mantle and crust continued to gradually cool, the researchers think.

Finally, about 750 million years ago, the supercontinent started to break up when tectonics shifted into overdrive. The researchers think this time period is when the mantle was finally cold enough for Earth's crustal plates to be destroyed at subduction zones. The supercontinent started to tear apart, creating new ecosystems for life to occupy.

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Original article at Live Science's Our Amazing Planet.

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