\" \" This is a model of Earth's core at China's Nanjing Geological Museum. The outer core is an iron-and-nickel alloy that serves as a buffer between the inner core and Earth's mantle, a layer of magma and molten rock. The inner core is a solid, iron-rich ball that's about 750 miles (1,200 kilometers) thick and 1,802 miles (2,900 kilometers) below Earth's surface. With all the talk these days about the harmful effects of global warming, you might assume that Earth's core could stand to chill out a bit. Like the planet itself, Earth's core is constantly spinning – some scientists think it's moving even faster than the rest of the planet.