Impact Craters and the Relative Ages of Earth and Moon

Abstract

RECENT aerial photographic and ground studies of islands in the Lake of the Woods area of the Canadian Shield have revealed a series of arcuate ridges which together make up a conspicuous circular feature 16 km in diameter (Fig. 1). The appearance of these ridges suggests that they are igneous intrusions which have been constrained to conform to a circular pattern with predominantly outward dipping layers by distortions in the Earth's crust produced by an ancient meteorite impact. The ridges are composed almost entirely of gneiss or granite gneiss similar to rocks immediately outside the circle and in many other areas of the Canadian Shield. A “volcanic” phenomenon of this character could reasonably be explained by supposing that the magma feeding the intrusions was at a relatively shallow distance beneath the surface. This in turn suggests that the feature may have been formed at a very early period in the history of the Earth's crust before solidification had proceeded to any great depth.