Apr. 24, 2006
Libya's Kebira Crater
A huge crater in the Sahara
desert, said to be the largest one ever found in the region, and
dwarfing Arizona's "Meteor Crater", poses new questions for geologists.
Is the crater related to the origins of the mysterious "desert glass" in
Scientists suggest that a meteorite impact millions of years ago is the
cause of the giant crater imaged above. Recently discovered in satellite
images of the area, the crater lies in Egypt's western desert. It is
some 19 miles (31kilometers) wide and is said to be the impact site of a
meteoric intruder perhaps three-fourths of a mile (1.2 kilometers) in
diameter. The crater itself is more than 25 times the size of Arizona's
famous Meteor Crater. But over time, erosion by wind and water largely
obscured the ancient scar.
One intriguing aspect of the discovery is its close association with a
mysterious field of yellow-green glass, broken into large chunks,
littering the dunes in the Great Sand Sea of southwestern Egypt.
The first report of the yellow-green “desert
glass” came from Patrick Clayton in 1932, following his excursion
through the Saad Plateau near the Kebira Crater site. At the time, the
origin of the glass was unknown: There was no evidence of geological
forces that could have melted the silica sand into glass. With Kebira’s
discovery, a hypothetical source for the glass is now available.
Geologists speculate that the glass originated as ejecta from the Kebira
impact. It is thought that the meteor strike imparted so much energy to
the surrounding silica sand that it was melted and then explosively
hurled outward, solidifying and fracturing into shards, as depicted
Although the glass is most likely a result of Kebira, the method by
which it was created is open to question.
1. The glass is too pure – some of the purest natural silica glass ever
found. If the glass shards are tektites (melted slag from volcanoes or
meteor impacts), they should include the presence of other minerals.
2. The glass does exhibit small internal bubbles that include other
elements. One of those elements is iridium, the presence of which
indicates an extra-terrestrial origin, according to prevailing theories
(see Alvarez, Luis W., et al. "Extraterrestrial Cause for the
Cretaceous-Tertiary Extinction: Experimental Results and Theoretical
Interpretation." Science 208 (1980) 1095-1108). However, the glass
reveals no evidence of other minerals found in the region, such as
halite and alumina.
3. Another area where this type of glass may be found is
atomic test sites.
If the explosion of a solid object, like a meteor, did not form the
glass, then there remains one other method available—an enormous
electrical discharge. The glass shards, then, are the remains of large
Fulgurites are created when bolts of lightning strike refractory
minerals in the earth, instantaneously smelting the minerals into other
forms, such as cristobalite. The yellow-green glass does, in fact,
contain cristobalite inclusions, along with the iridium and other
platinum family elements.
If one grants the power of a lightning bolt large enough to form an
impact site some 19 miles in diameter, then additional possibilities
must also be considered. Electrical theorists have long claimed that
highly energetic electric discharge transmutes elements—a process that
is going on all the time on the surface of stars, they contend. The same
thing is implied on Jupiter's moon Io, where electric discharge appears
to be continuously transmuting oxygen from water ice into sulfur. (The
association of energetic lightning strikes with a "sulfurous stench" is
much more than an old wives' tale, the electrical theorists say).
Is the Kebira site the scar of a cosmic thunderbolt? If so, new
directions of investigation will be essential.