Formation of embryos of the Earth-Moon system as a result of a collision   of two rarefied condensations
  The angular momentum of the present Earth-Moon system could be acquired at the collision of two identical rarefied condensations with sizes of Hill spheres which total mass was about 0.1 of the mass of the Earth. Solid embryos of the Earth and the Moon could be originated as a result of contraction of the condensation formed at the collision. Depending on eccentricities of planetesimals that collided with solid embryos of the Earth and the Moon, the Moon could acquire 0.04-0.3 of its mass at the stage of accumulation of solid bodies while the mass of the growing Earth increased by a factor of ten. 
S.I. Ipatov
astro-ph.EP