answers.input_text: short
answers.span_text: an iron -- nickel alloy and some other elements
questions: what is the inner core of the earth made from
name: Inner core
contexts: The Earth 's inner core is the Earth 's innermost part . It is primarily a solid ball with a radius of about 1,220 kilometres ( 760 miles ) , which is about 70 % of the Moon 's radius . It is composed of an iron -- nickel alloy and some other elements . The temperature at the inner core 's surface is approximately 5,700 K ( 5,430 ° C ) , which is about the temperature at the surface of the Sun .