Final answer:
Increasing the iron composition of Earth's crust leads to an increase in density due to iron's inherent denseness. While the crust's melting temperature may rise slightly with more iron, the crust's temperature is mainly influenced by heat from the mantle. Differentiation during the planet's formation led to iron-rich cores and less dense crustal compositions.
Step-by-step explanation:
When the iron composition of Earth's crust increases, the density of the crust increases as well. This is because iron is a dense metal, and when it is a significant component of crustal material, it adds to the overall mass per unit volume, thereby increasing the density. In terms of temperature, the melting point of iron is high, so an increased iron content could result in a higher melting temperature for the crustal rock in which it is contained. However, the overall temperature at which the crust exists is more dependent on external sources of heat, such as the mantle beneath it, rather than its composition.
The process responsible for the distribution of iron within the Earth's crust and mantle is known as differentiation, a phenomenon where, during the early stages of a planet's formation, it becomes warm enough for its interior to melt, allowing heavier elements like iron to sink towards the center, forming a dense core. This is why we find iron predominantly in the Earth's core, and only a fraction of it within the crust. Overlying materials can compress the crustal matter, and as compression increases with depth, so does density.