How did we discover the origin of these rare and mysterious pieces?

How did we discover the origin of these rare and mysterious pieces?

The Great Sand Sea Desert extends over an area of ​​72 thousand square kilometers, linking Egypt and Libya. If you find yourself in a certain part of the desert in southeastern Libya and southwestern parts of Egypt, you will notice pieces of yellow glass scattered across the sandy landscape.

It was first described in a scientific paper in 1933 and is known as Libyan Desert Glass. They are prized by mineral collectors for their beauty, relative rarity, and mystery. A pendant found in the tomb of the Egyptian Pharaoh Tutankhamun contains a piece of glass. Natural glasses exist elsewhere in the world; Examples include moldavite from Rees Crater in Europe and tektites from Ivory Coast. But none of them are as rich in silica as Libyan desert glass, nor are they found in such large masses and quantities.

The origin of glass has been a topic of debate among scholars for nearly a century. Some have suggested that it may be from volcanoes on the moon. Others suggest that it is the product of lightning strikes (“fulgurite” – glass that forms from the fusion of sand and soil as it is struck by lightning). Other theories indicate that it is the result of sedimentary or hydrothermal processes; Caused by a massive meteorite explosion in the air; Or it came from a nearby meteorite crater.

Now, thanks to advanced microscopy technology, we think we have the answer. In collaboration with colleagues from universities and scientific centers in Germany, Egypt and Morocco, I have identified Libyan desert glass as having originated from a meteorite impact with the Earth’s surface.

Space collisions are a fundamental process in the solar system, in which planets and their natural moons accrete asteroids and planetary embryos (also called planetesimals) collide with each other. These effects helped our planet come together, too.

Under the microscope

In 1996, scientists determined that the age of the glass was close to 29 million years. A later study indicated that the source material was composed of quartz grains, coated with mixed clay minerals and oxides of iron and titanium.

This latest discovery raises further questions, since the proposed age is older than the corresponding source material in the related area of ​​the Great Sand Sea Desert. Quite simply: those source materials did not exist at that location 29 million years ago.

In our recent study, one of the authors obtained two pieces of glass from a local resident who collected them in the Al-Jawf region in southeastern Libya.

We studied the samples using cutting-edge transmission electron microscopy (TEM) technology, which allows us to see tiny particles of the material – 20,000 times smaller than the thickness of a sheet of paper. Using this super-magnification technique, we found tiny minerals in this glass: different types of zirconium oxide (ZrO₂).

Minerals are composed of chemical elements, whose atoms form regular three-dimensional packages. Imagine placing eggs or soda bottles on a supermarket shelf: layers upon layers to ensure the most efficient storage. Likewise, atoms combine to form a crystal lattice unique to each mineral. Minerals that have the same chemical composition but different atomic structure (different ways of packing the atom into the crystal lattice) are called polymorphs.

One of the many forms of ZrO₂ that we have observed in Libyan desert glass is called cubic zirconia, the type that appears in some jewelry as an artificial substitute for diamonds. This metal can only form at a high temperature between 2250°C and 2700°C.

Another polymorphism of ZrO₂ that we have observed that is very rare is called ortho-II or OII. It forms at very high pressure – about 130,000 atmospheres, which is a unit of pressure.

These pressure and temperature conditions have provided us with evidence for the origin of the meteoric glass impact. This is because such conditions can only be obtained in the Earth’s crust by a meteorite collision or the explosion of an atomic bomb.

More puzzles to solve

If our findings are correct (and we believe they are), the parent crater — where the meteorite hit the Earth’s surface — should be nearby. The closest known meteorite craters, called GP and Oasis, are 2 km and 18 km in diameter respectively, which is very far from where the glass we tested was found. They are too remote and too small to be considered the parent craters of such vast amounts of impact glass, all concentrated in one place.

Great Sand Sea Desert.  Sylvester Adams

Great Sand Sea Desert. Sylvester Adams

So, while we’ve solved part of the puzzle, other questions remain. Where is the paternal hole? How big is it – and where is it located? Could it have been eroded, distorted, or covered in sand? Further investigations will be needed, most likely in the form of remote sensing studies coupled with geophysics.

This article is republished from The Conversation, an independent, nonprofit news organization that brings you trustworthy facts and analysis to help you understand our complex world. The Conversation has a variety of great free newsletters.

Written by: Elizaveta Kovaleva, University of the Western Cape.

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Elizaveta Kovaleva receives funding from the Alexander von Humboldt Foundation.

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