PART 3
Impacts and Craters
The nearest large meteorite crater is some 90 miles to the west in Libya, but there is no evidence of impact glass at the site. In fact there are two other moderate sized craters in the vicinity of the glass - the largest being half a mile in diameter - but neither are large enough to explain the phenomenon. It would however be a remarkable coincidence to find such unusual material as LDG so close to relatively rare structures like astroblemes (deeply eroded impact features) without there being at least some relationship.
There has been no significant disruption to the surface rocks in the region, but this might be explained by the likelihood that the meteorite concerned exploded in mid-air above the desert (a so-called "soft impact"). This kind of event could certainly have been energetic enough to turn much of the desert sand and some of the bedrock into a vast lake of molten glass without necessarily moving it far from its original location, producing a large crater or leaving behind significant detectable quantities of extra-terrestrial debris.
Recent research by Mark Boslough of Sandia National Laboratories (working under contract to the US Department of Energy) concluded that the event which produced the glass was consistent with a 400 foot diameter asteroid entering the Earth’s atmosphere almost vertically at a speed of 12 miles per second, which broke up just before hitting the ground.
Such an impact would have generated a fireball that remained in contact with the Earth's surface at temperatures exceeding the melting temperature of quartz for more than 20 seconds – an effective yield of about 150 Megatons of TNT. Not only is this about 12,000 times the energy level the atomic bomb dropped on Hiroshima but, unlike a bomb-burst, the energy would all have been concentrated downwards. Momentarily, the temperature at the impact site would have been as hot as the surface of the Sun.
Afterwards, the molten glass may have flowed into low areas, puddled and cooled, gradually being broken up into smaller pieces by weathering. Certainly, rivers existed in this area in prehistoric times and these may also have assisted in breaking up and redistributing the glass.
Philippe Paillou of the Observatoire Aquitain des Sciences de L'Univers concluded that the Gilf Kebir was the largest impact crater field on Earth, based on the presence of numerous other smaller craters over the entire area. Collectively, these craters may well represent a series of multiple impacts all arising from a single meteorite shower.
In 2006, former NASA planetary scientist Farouk El-Baz, now a research Professor at Boston University, published what he claimed to be the definitive evidence for the impact theory – the discovery of the largest crater yet found in the Sahara.
The double-ringed structure is 20 miles in diameter across its outer rim, which is certainly large enough to be the source of the glass, if it is indeed a crater. Although located on the Gilf Kebir plateau, it is about 60 miles from the main concentration of glass. Given that there is no evidence of LDG travelling great distances through the atmosphere, we must speculate that either a vast shallow lake of molten material was formed which spread over this huge distance or that the LDG has subsequently been broken up and transported (perhaps by ancient rivers).
This as yet unconfirmed crater has been named "Kebira" (Arabic for "great" or "powerful"). While the extreme drought conditions of the Sahara generally act to preserve impact crater structures, El-Baz asserts that Kebira was difficult to see - partly because of its large size and partly because of its dissection and partial erosion by ancient rivers during a time when the region was considerably wetter than it is now.
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