Remote sensing studies of impact craters: how to be sure?

Abstract

After previous studies on impact craters in the eastern Sahara, particularly in Chad [2,15] and Libya [1], the paper by Paillou et al. [11] provides a good opportunity to discuss some important aspects of impact craters. They are a dominant landform on our Moon, and on other atmosphereless bodies (including planets and the satellites of planets) in our solar system. On the Earth, impact craters are far less obvious, and only about 170 structures have so far been confirmed to have been formed by hypervelocity impact. The diameters of these terrestrial impact craters range from less than 100 m to about 200 km; a couple of these structures have originally been even larger, probably about 250 to 300 km in diameter. The reason why we do not see more obvious impact craters on the surface is the Earth is intimately connected to the reason why it is such a suitable place for life: the Earth is a geologically active planet. The forces that shape our planet – for example, tectonics, volcanism, erosion, water, and weather – are those that obliterate the traces of even large-scale and devastating impact scars after geologically short time scales. This is probably one of the reasons why it took geologists so long to accept the reality of impact craters on Earth. A clear hiatus in the history of impact-related studies was the realization, around 1980, that CretaceousTertiary (K/T) boundary rocks bear unambiguous evidence for a large-scale catastrophic impact event; this was followed in the early 1990s by the discovery of the ca. 200-km-diameter Chicxulub impact structure, Mexico, as the source of the world-wide impact ejecta.