The term impact structure is closely related to the terms impact crater or meteorite impact crater, and is used in cases in which erosion or burial have destroyed or masked the original topographic feature with which we normally associate the term crater. This is the fate of almost all old impact craters on Earth, unlike the ancient pristine craters preserved on the Moon and most other geologically inactive rocky bodies with old surfaces in the Solar System. Impact structure is synonymous with the less commonly used term astrobleme meaning "star wound".
In an impact structure, the typical visible and topographic expression of an impact crater are no longer obvious. Any meteorite fragments that may once have been present would be long since eroded away. Possible impact structures may be initially recognized by their anomalous geological character or geophysical expression. These may still be confirmed as impact structures by the presence of shocked minerals (particularly shocked quartz), shatter cones, geochemical evidence of extraterrestrial material or other methods.
Famous quotes containing the words impact and/or structure:
“Television does not dominate or insist, as movies do. It is not sensational, but taken for granted. Insistence would destroy it, for its message is so dire that it relies on being the background drone that counters silence. For most of us, it is something turned on and off as we would the light. It is a service, not a luxury or a thing of choice.”
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