What fuels the lava at the earth's core?

All macro bodies are under constant gravitational collapse. Gradually, size of the macro body reduces and internal pressure (and heat) increases. Depending on the 3D matter-content of the body and the state of compression, physical state of its internal core changes. This mechanism is applicable to all macro bodies. read more

The Earth’s core is only partially molten. The outer core is composed of molten iron and nickel, and the inner core is solid. The inner core has grown at the expense of the outer core over the 4.5 billion years of the Earth’s history. Ultimately the core will entirely solidify, but this event will occur only in the far geological future. read more

The outer core surrounding it is an ocean of liquid metal 2,300 kilometers thick. The Earth's rotation makes this ocean flow and swirl, and the moving metal generates the planet's magnetic field. Most of Earth's heat is stored in the mantle, Marone says, and there are four sources that keep it hot. read more