Earth's iron core and reduction potential

Something that has always baffled me is, how could the earth form an iron core when there is so much oxygen present within the mantle and on surface of the earth? Wouldn't the formation of a metallic iron core have required a very substantal reduction potential?

In other words, if one was to take all the average ingredients of the earth, and then heat and pressurize it, the iron would a very strong dominating reducing agent like hydrogen or carbon to be added to keep it from staying oxidized. With the core 1000 larger than the surface water, there should be a lot more hydrogen, carbon, etc., type compounds on/within the earth, maybe 1000-10000 times more. Venus can hold a lot of atmosphere such that all the resultant water and CO2, from the reduction, should be much higher on the surface.