Earth's Core: A Sun-Temp Solid Iron Ball Forged by Crushing Pressure

Earth’s inner core is a solid iron-rich sphere kept solid not by coolness but by the planet’s crushing pressure, which raises iron’s melting point above the extreme temperatures at the boundary; seismic data and high-pressure experiments place the inner-core boundary at about 5,150 km deep with temperatures roughly in the thousands of kelvin (about 5,400–6,230 K), similar to the Sun’s surface in scale, while the outer core remains liquid. The core is likely an iron-nickel alloy with lighter elements, and the evidence comes from seismology, PREM models, and laboratory experiments rather than any core samples.