Definition: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Input: An ongoing debate concerns whether the outermost shell of this layer contains an anomalous ultra low-velocity zone. The boundary between this layer and the layer above it is home to a whispering-gallery mode called the SmKS mode. PKNP waves with N equals four and seven are multiply reflected when bouncing around this layer. The boundary between this layer and the layer above it refracts PKIKP waves. When they enter this layer, SKS and SKKS waves convert to P waves, and P-wave velocity increases smoothly with depth in this region. S wave velocity (*) drops to zero in this region, which lies immediately underneath the d-double prime layer of another region. Convection currents in which are the drivers in the dynamo theory of the Earth's magnetic field. For 10 points, name this 1400-mile thick layer of the earth bound from above by the Gutenberg discontinuity, which consisting of liquid iron and nickel.
Output:
Science