Figure 5-10 Chemical Differentiation and Earth’s Internal Structure (a) The newly formed Earth was molten throughout its volume. Dense materials such as iron sank toward the center, while low-density materials rose toward the surface. (b) The present-day Earth is no longer completely molten inside. A dense, solid iron core is surrounded by a less dense liquid core and an even less dense mantle. The crust, which includes the continents and ocean floors, is the least dense of all; it floats atop the mantle like the skin that forms on the surface of a cooling cup of cocoa.