19042

The brief article on the discovery of sheets of melted sand in Australia mentioned several possible sources of the heat that produced this material, but it failed to mention the most probable source–the impact of a comet on the upper atmosphere. The nature of comets is that when they encounter an atmosphere of significant density they deposit their considerable energy in that atmosphere at high altitude and leave little or no solid debris. We have evidence of this happening at the Tunguska site in Siberia. The article is tantalizing in that it gives no information about the area over which this glass can be found.

George Prehmus
Prescott, Ariz.

Although the burst of a comet on the upper atmosphere would have provided enough heat to fuse the glass, the researchers note that such an air burst probably wouldnt have generated the intense pressures needed to shock the quartz grains trapped in the material. Those conditions could only come from some sort of an impact with the ground, an extremely close call from a low-flying meteor, or both. –S. Perkins