As a geophysicist with a deep understanding of the Earth's structure, I can explain why the inner core remains solid despite the extreme temperatures it experiences. The key concept here is the interplay between temperature and pressure. While it's true that higher temperatures generally lead to a phase change from solid to liquid, the pressure exerted on a substance can counteract this effect. In the case of the Earth's inner core, the pressure is incredibly high due to the weight of the material above it. This high pressure allows the iron and nickel to remain in a solid state even though the temperature is extremely high, exceeding 5000 degrees Celsius. So, the reason the inner core is solid despite being the hottest part of the Earth is because the pressure is also higher there, which allows for the existence of solid iron-nickel at these extreme temperatures. read more >>

Answer 3: It turns out that many materials can be a solid at a higher temperature if the pressure is also higher. So, even though it is hotter in the inner core, the pressure in the core is also higher, and you can have solid iron-nickel instead of liquid.read more >>