How much water was delivered from the asteroid belt to the Earth after its formation?

The Earth contains between 1 and 10 oceans of water, including water within the mantle, where 1 ocean is the mass of water on the Earth's surface today. With N-body simulations, we consider how much water could have been delivered from the asteroid belt to the Earth after its formation. Asteroids are delivered from unstable regions near resonances with the giant planets. We compare the relative impact efficiencies from the nu(6) resonance, the 2:1 mean motion resonance with Jupiter and the outer asteroid belt. The nu(6) resonance provides the largest supply of asteroids to the Earth, with about 2 per cent of asteroids from that region colliding with the Earth. Asteroids located in mean motion resonances with Jupiter and in the outer asteroid belt have negligible Earth-collision probabilities. The maximum number of Earth collisions occurs if the asteroids in the primordial asteroid belt are first moved into the nu(6) resonance location (through asteroid-asteroid interactions or otherwise) before their eccentricity is excited sufficiently for Earth collision. A maximum of about eight oceans of water may be delivered to the Earth. Thus, if the Earth contains 10 or more oceans of water, the Earth likely formed with a significant fraction of this water.