Most schoolchildren learn that the Earth has three (or four) layers: a crust, mantle and core, which is sometimes subdivided into an inner and outer core. That's not wrong, but it does leave out several other layers that scientists have identified within the Earth, including the transition zone within the mantle. In a new National Science Foundation-funded study, researchers use data from an enormous earthquake in Bolivia to find mountains and other topography on the base of the transition zone, a layer 660 km (410 miles) straight down that separates the upper and lower mantle. To peer deep into the Earth, scientists use the most powerful waves on the planet, which are generated by massive earthquakes. The researchers were surprised by just how rough that boundary is -- rougher than the surface layer that we all live on. Their statistical model didn't allow for precise height determinations, but there's a chance that these mountains are bigger than anything on the surface of the Earth. The roughness wasn't equally distributed, either; just as the crust's surface has smooth ocean floors and massive mountains, the 660-km boundary has rough areas and smooth patches. The researchers also examined a layer 410 km(255 miles) down, at the top of the mid-mantle "transition zone" and they did not find similar roughness.
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