LouisZepher: Mohorovicic Layer, or something different? Tfa doesn't say.

From what I gathered, the standard model is that the crust sits directly upon a not quite molten mantle which, while not liquid, is hot and soft enough to plasticly deform over reasonably long periods of time, thus allowing things like plate tectonics to happen.

However, they've discovered that something like half the Earth's crust sits on a thin layer of more molten rock floating on top of the mantle, which they originally thought only occurred in small areas.  Still not exactly liquid like magma, but more so than the mantle usually is.

Or something like that.