The layer with the most iron is the Earth's core. Both the inner and outer cores are primarily composed of iron and nickel. They are incredibly hot, with temperatures ranging from 7200–9000℉ (4000–5000℃).
While iron can be found in other parts of the Earth, such as the mantle and crust, its concentration is significantly higher in the core. The Earth's core is believed to be mostly composed of iron, with a smaller amount of nickel and trace amounts of other elements.
The immense pressure in the Earth's core causes the iron to solidify, even though the temperature is extremely high. This solid inner core is surrounded by a liquid outer core, which is also primarily composed of iron.
