The Earth is a gigantic ball of semi-molten rock, with a heart of iron as hot as the surface of the Sun. Titanic amounts of heat left over from its birth and the radioactive decay of trillions of tons of radioactive elements find no escape but up. Currents of rock spanning thousands of kilometers carry this energy to the surface. Earth’s crust is the only thing in their way. It feels solid to us, but it is only a fragile barrier, an apple skin around a flaming behemoth. True apocalypses can break through and unleash eruptions tens of times more powerful than all of our nuclear weapons combined, subjecting the climate to centuries worth of change in a single year, while drowning continents in toxic ash and gases: supervolcanoes. How big can they get? And will they put an end to humanity?