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uni'wissen 02-2013_ENG

Fifteen million years ago in southwestern Ger- many: A stony meteorite with a diameter of 1.5 kilometers is on a collision course with the Earth. Even before it hits, a shock wave pulver- izes the primeval forest. This airburst occurs as the meteorite enters into the Earth’s atmosphere. Everything that survives the blast is reduced to ashes by the heat radiating from the point of im- pact. At the moment the meteorite reaches the Earth’s surface, the energy of the impact is trans- ferred to the stone. It breaks, melts, and fumes; a glowing cloud billows up from the ground. The rest of the energy is transferred into motion: The Earth trembles. This shock wave catapults soil and rock from the point of impact into the air. Rocks the size of a house are hurtled as far as 40 kilometers away. A round crater, roughly 4.5 kilo- meters deep and twelve kilometers wide, takes shape for a brief moment, only to cave in under the influence of gravity. The final crater, the Nördlinger Ries, is only 500 meters deep but has a diameter of 25 kilometers. The large circular depression between the Franconian and Swabian Jura was long thought by scientists to be the weathered remains of a volcanic crater. It wasn’t until the 1960s that ge- ologists ascertained that the basin-shaped valley was created by the impact of a meteorite. They discovered coesite and stishovite at the site – Thomas Kenkmann simulates meteorite impact events in the lab Geology in Fast Forward by Mathilde Bessert-Nettelbeck high-pressure minerals found only in places where a meteorite has compressed the rock to an extreme extent and left a crater. Prof. Dr. Thomas Kenkmann from the Institute of Earth and Environmental Sciences of the Uni- versity of Freiburg wants to understand the pro- cess by which craters and high-pressure minerals, also known as impactites, form when a meteorite collides with the Earth. Most geological changes are extremely long, drawn-out processes in which rock is transformed and shifted by various forces, movements in the Earth’s crust, and chemical re- actions over the course of millions of years. In im- pact craters this all happens in fast forward. In the case of the Nördlinger Ries, for instance, the im- pact and the entire process of crater formation lasted approximately 50 seconds. “It’s a geology of seconds,” says Kenkmann. In order to reach a better understanding of the process by which such craters are formed, geolo- gists can’t wait for something new to drop from the sky. Instead, Kenkmann falls back on a minia- ture model. He conducts simulations with his re- search group, “Multidisciplinary Experimental and Modeling Impact Research Network” (MEMIN), funded by the German Research Foundation. The cooperation between scientists of the Univer- sity of Freiburg and the Fraunhofer Association’s © Fraunhofer EMI 4