Terrestrial worlds are 28% iron by mass*. The Solar nebula was 0.11-0.13% iron by mass**. Assuming that the early Earth kept all of its iron: Msub-nebula x 0.0012 = Mearth x 0.28Thus: Msub-nebula = Mearth x 230There are ~2.0 Earth-masses of rocky bodies in the Inner Solar System. Thus, those ~2.0 Earth masses of rock condensed out of ~460 Earth-masses of sub-nebular gases. This is comparable to the combined masses of Jupiter & Saturn. So, perhaps Jupiter & Saturn accumulated their material from the Inner Solar System. This also suggests that Jupiter's rocky core is only about 1.5 Earth-masses, that Saturn's rocky core is only about 0.5 Earth-masses, while those of Uranus & Neptune are more like Mars in size. * S.N. Raymond, et al. Exotic Earths: Forming Habitable Worlds with Giant Planet Migration, pg. 13. (See: http://arxiv.org/PS_cache/astro-ph/pdf/0609/0609253v1.pdf ) ** http://www.kayelaby.npl.co.uk/chemistry/3_1/3_1_3.html ; http://astro.uni-tuebingen.de/~rauch/TMAP/UserGuide/UserGuidese12.html X = 0.735 Y = 0.248 Z = 0.017 S.F. Green, et al. An Introduction to the Sun and Stars, pg. 46.