What tells us that the inner core is made up of iron?

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Some of the best evidence that the earth's inner core is composed of iron is based on a calculation of the earth's density using the earth's size and gravitational pull. After calculating the earth's density, we know that iron is the material that gives the best estimate of the earth's weight. In addition, seismic waves moving through the earth's core travel at a velocity that is dependent on the material they move through. Iron represents the material that is the best fit with the velocity of the seismic waves moving through the earth's core. Finally, iron is one the most plentiful elements on earth, and many asteroids are also composed of iron. Scientists think that earth might have been formed in part from the merging of asteroids, so it would make sense that the earth's core is made up of iron as well. 

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