During the last three years I have been trying to place the giant impact theory for the origin of the Moon on a more quantitative basis. This means that the angular momentum in a collision of another planetary body with the protoearth should lie in the range 1.0 to 1.25 times the present angular momentum of the system (a little angular momentum has been lost to solar tides) and significantly more than a lunar mass of material should be left in orbit (because lunar accumulation will be inefficient) and it should be substantially iron-free. These conditions cannot be met if the giant impact occurs when the Earth is fully assembled. So my numerical simulations now span the range of 0.5 to 1.0 Earth masses involved in the impact with the above values of angular momentum with a mass ratio of protoearth to impactor of 7:3. The conditions are best satisfied for a total mass at impact of about 0.65 Earth masses. We now know from Hf-W dating that the giant impact occurred some 50 million years after the formation of the solar system. These findings have a profound influence on the developmental history of the Earth, which I shall describe.