SEMINAR - Christian Koeberl

Meteorite impact cratering on Earth:
Geological and biological consequences

Dr. Christian Koeberl
Department of Geological Sciences
University of Vienna, Austria

Wednesday, December 5th, 1:00pm GMCS 422

Impact is a unique, short-time, high-energy geological process. The importance of impact cratering on terrestrial planets (Mercury, Venus, Mars), our Moon, and the satellites of the outer planets is obvious from the abundance of craters on their surfaces. On most bodies of the solar system that have a solid surface, impact cratering is the most important surface-modifying process even today. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth’s surface. They come in various forms, shapes and sizes, from 300 km to less than 100 m in diameter, from Recent to 2 billion years in age. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions. In this lecture we will take a look at impact craters on the Earth (and some other planets), and discuss how they formed and how they can be recognized. An aspect of impact cratering that may be underestimated is the influence of impacts on the geological and biological evolution of our own planet. Even the impact of relatively small asteroids or comets can have disastrous consequences for our civilization. There is a 1 in 10,000 chance that a large asteroid or comet 2 km in diameter (corresponding to a crater of about 25-50 km in diameter) may collide with the Earth during the next century, severely disrupting the ecosphere and annihilating a large percentage of the Earth's population. The biological evolution of our planets is punctuated by mass extinction events, of which the one 65 million years ago, which marks the Cretaceous-Tertiary boundary, is probably the best known one. Abundant impact debris marks this boundary, providing a clear link with a major impact event. The Chicxulub impact structure in Mexico, about 200 km in diameter, which resulted from the impact of an about 10-km-diameter asteroidal body, has been identified as the culprit. Understanding of impact structures, their formation processes, and their consequences should be of interest not only to earth and planetary scientists, but also to society in general.


Christian Koeberl is a professor at the Department of Geological Sciences at the University of Vienna, Austria, whose main research interest is the interdisciplinary study of meteorite impact craters, including shock petrography and the geochemistry of impactites, and also works on meteorites. He was the chairman of the European Science Foundation (ESF) “IMPACT” program (1998-2003), and is a member of the International Continental Scientific Drilling Program (ICDP) Science Advisory Group. He has published over 300 peer-reviewed research papers and has written or edited 12 books.