Re:It CANNOT be THAT different.. (Score 1)

There are several places on earth where very violent and deep volcanoes bring chunks of mantle up to the surface, so we don't have to drill to the mantle to know what it is made of. Also we know a lot about the earth's interior from seismic waves-more than "average" density. As far as the exact chemical composition of the core, you're right that there's a bit of guessing involved.