Migration processes of comets and asteroids from the outer regions of the solar system, including the Edgeworth–Kuiper belt, are regarded as important mechanisms for the formation and evolution of the inner planets. These minor bodies may be responsible for the delivery of volatile matter to the inner planets and thus be responsible for the origin of life. We estimate that the cumulative mass of icy comets impacting on the Earth during the formation of the giant planets is similar to the mass of water in the Earth oceans, and that Mars acquired more water per unit planet mass than Earth. We find that these cometary objects mostly evolved from typical near-Earth orbits and Encke-type orbits with aphelia located inside the orbit of Jupiter, and played a greater role than those with Jupiter-crossing orbits. The relative importance of comets and chondrites in the delivery of volatiles is constrained by the observed fractionation patterns of atmospheric noble gas abundance.