 The inner core is buried approximately 3,220 miles deep inside the earth. I don't know how we know this. The solid metal, did we put a big spike in there? Solid metal ball is mostly comprised of iron and nickel. The inner core is estimated to reach temperatures as scalding as the surface of the sun, roughly 9,800 degrees Fahrenheit. And this all just happened because of a big bang? Is that how this happened? That's what they say.