After a large collision in the asteroid belt some 470 million years ago (in Ordovician times), many asteroid fragments were tossed into Earth-crossing orbits, collided with the Earth, and produced impact craters. The 54 kilometer-in-diameter Charlevoix impact structure in Quebec, Canada, was formed then, based on new uranium-lead dating of zircon grains, led by Martin Schmieder at the Lunar and Planetary Institute in Houston. However, this giant impact crater didn’t last long. Soon after its formation, it was buried and deformed by the plate-tectonic processes that built the early Appalachian Mountains. The crater is visible now on the north shore of the St. Lawrence River because the Appalachian-age sediments have been eroded away.
Source: Schmieder, M., Shaulis, B.J., Lapen, T.J., Buchner, E. and Kring, D.A., 2019. In situ U–Pb analysis of shocked zircon from the Charlevoix impact structure, Québec, Canada. Meteoritics & Planetary Science (in press), DOI: 10.1111/maps.13315.