Libya: These yellow glass fragments in the desert are witnesses to an unknown asteroid impact – Futura

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In 1933, scientists discovered numerous strange small pieces of yellow glass in the sand during an expedition to the Libyan desert. Results from the fusion of rocks containing silica, natural glasses are not particularly rare. They can actually be found in many places around the world. However, their formation requires high temperatures, which explains why the glasses generally occur in volcanic contexts or meteorite impacts.

A controversial origin

However, the fragments discovered in the Libyan desert are in no way linked to a volcanic eruption and appear to be very different from the usual tektites formed by meteorite impacts. Libyan glasses actually contain much more silica than the latter. They also occur in large fragments and are found in large quantities in the desert. Some studies have concluded that they could be fulgurites, glasses formed by the fusion of sand during lightning strikes in the desert. A theory that, however, did not find unanimous support.

A meteorite impact, but no crater

Thanks to modern analysis techniques, the mystery could finally have been partially solved. A team of scientists has just discovered that these glasses were made at very high temperatures (around 2,500 °C) and very high pressure (130,000 atmospheres). The results were published in the journal American Mineralogist.

Extreme conditions that only occur during a meteorite impact or an atomic bomb explosion. But given the age of the glasses, which is 29 million years, this last hypothesis is finally invalidated! Although the origin of the fragments has now been clarified, the story still has some gray areas. In fact, no crater was found nearby. Given the amount of glasses, it should still be a considerable size. Therefore, further research is required to fully lift the veil on the origins of Libyan desert glass.

A meteorite impact is behind the secret of the yellow glass in the desert

Article by Laurent SaccoLaurent Sacco, published on May 20, 2019

Libyan glass is a natural rock found in the desert, mainly in Egypt. It is most likely the product of heat released upon the arrival of a celestial body. It is now believed that this heat was actually caused by the formation of an impact crater and not by an event similar to the Chelyabinsk meteorite.

As the name suggests, the “Great Sand Sea” of the Libyan Desert lies primarily in Egypt and flows only into Libya, Sudan and Chad. There is an oval region with a north-south extent of about 130 km (latitudes N 25°02′ – N 26°13′) and 50 km west-east extent (longitudes E 25°24′ – E 25°55). ‘). It is famous in the world of meteorite lovers because there you can discover samples of a strange yellow to light green rock with a more or less transparent appearance called “Libyque glass”.

For almost a century, this glass has fascinated naturalists such as Théodore MonodThéodore Monod, and there are good reasons to believe that, like the iron of Tutankhamun’s dagger, it has a meteoritic origin, albeit indirectly. In addition, Libyan glass was particularly known during the time of the Pharaohs because it was used to make the scarab that adorns the chest of Tutankhamun (born around -1345, died around -1327). In fact, it has obviously been used by humans for a long time, as many Libyan glass cutting sites are associated with the presence of prehistoric tools from the Neolithic period (9,000 BC), when there was then a “green” Sahara with rivers and lakes full of fish, and there lived people surrounded by elephants and hippos.

Libyan glass is 98% silica and 2% aluminum oxide and contains some traces of iron oxide, titanium titanium and zirconium zirconium. It was the potassium-argon method that made dating possible, but especially the fission trace method. We then obtain ages ranging from about 29.5 to 28.5 ± 0.4 million years. Several theories have been proposed to explain its origin, which can be divided into two classes: theories involving very terrestrial phenomena and theories involving the fall of a small extraterrestrial body, meteorite or comet.

Excerpt from the program Immediate catastrophe, meteorite impact. The Chelyabinsk meteor may have caused significant damage, as evidenced by craters left by impacts from other meteors. But the forces acting on the celestial object caused it to implode in the atmosphere.© Nat Geo France

An explosion of 100 megatons of TNT?

It was this last hypothesis that ultimately prevailed, but debate still rages over whether Libyan glass is the product of the fusion of terrestrial rocks during the formation of an impact crater or simply the product of radiation from a celestial body exploded in the atmosphere. In the latter case, researchers report the equivalent of the famous Tunguska explosion in 1908 and, more recently, the Chelyabinsk meteorite. This would have resulted in a fireball similar to that of a nuclear explosion, the thermal radiation of which would have heated the sands of the Sahara to form this glass, which is comparable to trinitite, a rock formed by exposing sand to the radiation of a nuclear explosion.

But the power of the explosion at the origin of the Libyan glass, 100 megatons, must have been much greater than that of June 1908 – the energy of which was estimated at 5 megatons of TNT, the equivalent of 600 Hiroshima-type bombs – and even more so that of June 15 February 2013 over the Russian city of Chelyabinsk, where around 30 Hiroshima-type bombs were dropped.

No impact crater from the Libyan Glass period has been found that could be linked to its formation, but the debate has undoubtedly just been raised by an article published in the famous journal Geology by two researchers, Aaron Cavosie of Curtin University in New York York, Rekindled USA, and Christian Koeberl, from the Natural History Museum in Vienna.

They examined zircon-zircon grains in Libyan glass samples and concluded that they had temporarily changed phase and turned into a type of mineral called reidite. It is named after scientist Alan F. Reid, who first created it in the laboratory under high pressure in 1969. In fact, it is a very rare mineral on the earth’s surface that only occurs in connection with impacts of celestial bodies.

This passage of zircons in their transition phase, corresponding to reidite, before returning to their original state, would not be possible with the pressures predicted by the hypothesis of an explosion in the atmosphere. So we would have finally decided between the two hypotheses, but we can bet that researchers will only be convinced once we have clearly identified a 29-million-year-old astroblema in the “Great Sand Sea” region of the Libyan Desert.