The high abundance of iron on the surface of mars is indicative of what difference between earth and mars?

Mars is known as the "Red Planet" because of an abundance of iron oxide on its surface.The high abundance of iron on the surface of mars is indicative of the fact that Mars never melted as extensively as Earth. Mars' smaller size (and weaker gravity) allowed it to remain less differentiated. 
But, despite Mars's high surface iron content, its overall magnetic field is weak compared to that of Earth. 

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