If we took a journey from Earth's surface to the center, the midway point is roughly at 1900 km depth in the lower mantle. The lower mantle ranges from 660 to 2900 km depth and occupies 55% of our planet by volume. The chemical composition of the lower mantle is rather simple. It has long been pictured as being made up of 2 major minerals (~95%), namely bridgmanite and ferropericlase. Recently, this model was directly challenged by a set of discoveries in the lower mantle.