Journal Highlights

Impact Geologists, Beware!

Commentary in Geophysical Research Letters

For decades now, impact crater geologists have relied on a seemingly infallible test for the pedigree of a suspected impact structure:  If you can find shock-metamorphosed minerals, especially quartz, then the structure was made by a forceful extraterrestrial impact onto our surface because no other known process could achieve the pressures necessary to alter quartz into one of several high-pressure forms, commonly referred to as “shocked” quartz.  This idea has continued to hold sway in the field in spite of a few cases where such quartz is found, but an impact origin seems unlikely [Haines et al., 2001; Schultz et al., 2004].  Now, a group at the University of Pennsylvania [Chen et al., 2017] has challenged this canon by demonstrating that, under the right circumstances, ordinary storm-generated lightning may produce shock lamellae in quartz. More…

By H. J. Melosh, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN

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