The term 'CENTER OF THE EARTH' can be summarized by the crossword solution 'CORE, ' which is a four-letter word. The CORE of the Earth is the innermost layer of the planet, located beneath the mantle and crust. It is composed of iron and nickel and is believed to be about 5, 000 kilometers in radius. The CORE is responsible for the Earth's magnetic field and is the source of most of the planet's seismic activity.