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The origin of continental nuclei has long been a puzzle. Theories advanced so far have generally failed to explain the first step in continent growth， or have been subject to serious objections. It is the purpose of this article to examine the possible role of the impact of large meteorites or asteroids in the production of continental nuclei. Unfortunately， the geological evolution of the Earths surface has had an obliterating effect on the original composition and structure of the continents to such an extent that further terrestrial investigations have small chance of arriving at an unambiguous answer to the question of continental origin. Paradoxically， clues to the origin and early history of the surface features of the Earth may be found on the Moon and planets， rather than on the Earth， because some of these bodies appear to have had a much less active geological history. As a result， relatively primitive surface features are preserved for study and analysis. In the case of both the Moon and Mars， it is generally concluded from the appearance of their heavily cratered surfaces that they have been subjected to bombardment by large meteoroids during their geological history. Likewise， it would appear a reasonable hypothesis that the Earth has also been subjected to meteoroid bombardment in the past， and that very large bodies struck the Earth early in its geological history. The large crater on the Moon listed by Baldwin has a diameter of 285 km. However， if we accept the hypotheses of formation of some of the mare basins by impact， the maximum lunar impact crater diameter is probably as large as 650km. Based on a lunar analogy， one might expect several impact craters of at least 500km diameter to have been formed on Earth. By applying Baldwins equation， the depth of such a crater should be about 20km. Baldwin admits that his equation gives excessive depths for large craters so that the actual depth should be somewhat smaller. Based on the measured depth of smaller lunar crater. Baldwins equation gives the depth of the zone of brecciation for such a crater as about 75km. The plasticity of the Earths mantle at the depth makes it impossible to speak of bracciation in the usual sense. However， local stresses may be temporarily sustained at that depth， as shown by the existence of deep-focus earthquakes. Thus， short-term effects might be expected to a depth of more than 50km in the mantle. | 
