Google's latest doodle honors the birthday in 1888 of geophysicist Inge Lehmann. In the 1930s seismologists were puzzled by the fact that P waves generated by earthquakes slowed down when they passed through certain regions of the inner Earth. 1936 Lehmann proposed an explanation, which was quickly accepted: Earth's core is not a single molten sphere; rather, it consists of an inner core and an outer core.
