As slabs of Earth's crust descend into the mantle, they encounter a zone about 1,100km down where the mantle rock abruptly becomes stiffer, flowing less easily. Rising plumes of molten rock encounter the same layer and have difficulty punching through from below; now researchers know why.

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As slabs of Earth's crust descend into the mantle, they encounter a zone about 1,100km down where the mantle rock abruptly becomes stiffer, flowing less easily. Rising plumes of molten rock encounter the same layer and have difficulty punching through from below; now researchers know why.