The Miracle Of Iron !!

[Darwinian]

I may be wrong and I'd have to look into it further (and I can't be bothered) but I don't think that the collision between Earth MKI and Thea actually provided any extra iron to the Earth as the impact, while completely liquifiying the early Earth back to a droplet of melt only stripped off the outer crust of the Earth.

This impact of course then helped to create Earth MKII which is now where we live and also formed the moon from all the debris.

Although I stand to be corrected.