Earth's inner core is hotter than the outer core. Why is it solid while the outer core is liquid? Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. a The higher pressure keeps it solid b It is made of a denser element with a higher melting point c It is actually cooler than the outer core d It is made of a rare material that solidifies when heated rather than melt e The inner core is still a liquid, but it flows slow enough to be considered a solid.