Precise measurements in earthquake timings have revealed that the Earth’s inner core, a solid ball of iron and nickel around 2,442 km (1,517 miles) across, is spinning slightly faster than the outer liquid core and the rest of the Earth. Each year the inner core moves ahead of the Earth’s surface by around 0.3-0.5 degrees – a rate of around 50,000 times the speed that the Earth’s continental plates move apart.