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Because as Earth cooled, dense metal like iron sank to the centre, while lighter rock-forming materials floated to the top. |
At the center of Earth is a solid iron inner core. The hot dense core has a radius of about 759 miles (1,221 kilometers) and a pressure of about 3.6 million atmospheres (atm).
Temperatures in the inner core are about as hot as the surface of the sun (about 9,392 degrees F or 5,200 degrees C) — more than hot enough to melt iron — but the immense pressure from the rest of the planet keeps the inner core solid, according to National Geographic.
The primary contributors to the inner core’s heat are the decay of radioactive elements such as uranium, thorium and potassium in Earth’s crust and mantle, residual heat from planetary formation, and heat emitted by the solidification of the outer core.
Earth’s inner core rotates in the same direction as the surface of the planet but rotates ever so slightly faster, completing one extra rotation every 1,000 years or so.
Credit: space.com
Picture credit: Google
