IMPACT MATERIALS AT ARCHEOLOGICAL SITES: A CRITICAL VIEW

The recent increase in reports of suggested impact materials at archeologic sites and the proposed link between comet or asteroid strikes and the destruction of cities to civilizations emphasizes the need for a critical review of diagnostic impact evidence particularly with regards to petrographic and geochemical data that may be mimicked by ancient to modern anthropogenic processes. Other authors have publicized in both popular online venues and the peer-reviewed possible evidence of impacts or air bursts associated with Tel al Hammam, Jordan; Abu Hureyra, Syria; Hopewell, Ohio; and Chiemgau, Germany.

Claims of impact rely heavily upon micro scale petrographic and geochemical analyses. Here we present a review of the accepted geological criterial for establishing evidence for an impact. This includes shock petrography (e.g., traditional shock metamorphic effects in minerals, specifically quartz, feldspar, and zircons), extreme melting associated with impact and/or airbursts, and micro-scale geochemical markers tied to the impactor.

Although geochemical markers and extreme temperature melts are sometimes used as unique indicators of impact in the ancient geologic record, these may not always be applicable when dealing with archeologic materials. Human generated melts and processed materials can achieve similar conditions to melting that occurs during an impact. Similarly, such operations can concentrate normally ‘exotic’ chemistries and therefore the use of geochemical tracers should be approached with caution.