The formation of Libyan Desert Grass (LDG) is at the center of great debate in planetary science. Lighting, strange geological processes, and even lunar volcanoes have been suggested as possible causes. Over the past 25 years, researchers have focused on his two scenarios. It is caused by a meteorite impacting the desert, or by a meteorite exploding in the air. New evidence suggests that the first hypothesis is probably correct.
Glass is made by melting sand, so most scenarios involved supplying large amounts of energy to the desert sands between Egypt and Libya. As for the temperature at which sand turns to glass, both meteorite impacts and atmospheric explosions can get there, as they can cause fusion at high temperatures.
“The main goal of our study was to distinguish between airbursts, such as those over Chelyabinsk or Tunguska, and impacts on the ground,” said the study’s lead author. Dr. Elizaveta Kobalevaa professor at the University of the Western Cape, told IFLScience.
Tutankhamun’s chest features a scarab carved from Libyan desert glass.
The team set out to find evidence that could distinguish one scenario from another. In fact, there is an important difference between a shock and an airburst. Despite the high temperatures and shock waves in the air, airbursts cannot transmit enough pressure into the ground to create shock minerals, so the researchers investigated the glass’s detailed composition.
An international team of researchers used transmission electron microscopy to study how minerals are organized within the material. In particular, they discovered small crystals of zircon oxide. Crystals can arrange the atoms inside them in different ways, and some arrangements only form under certain conditions.
One of the configurations found is known as cubic zirconia. This is commonly found in jewelry and is stable thanks to purposeful impurities. Here, the surrounding glass remains stable. It forms at high temperatures of 2,250 to 2,700 degrees Celsius (4,082 to 4,892 degrees Fahrenheit). However, the actual temperature may have been higher, based on the melting of other minerals found during the observations.
Although temperature indicators are not sufficient to distinguish between shocks and airbursts, another configuration of zirconia found within glass is much rarer and also suggests large shock pressures. Not only does this mineral require heat to form, but it also requires extremely high pressure, around 130,000 atmospheres. If the minerals in the glass were to form under such conditions, there is an obvious natural scenario of a meteorite impact.
“They are very small particles of mineral phase, and they form only at very high pressures. And such high pressures are only achieved within the Earth’s crust after a meteorite impact. Because of its small size, it was preserved in the LDG,” Dr. Kovaleva explained.
The evidence for impact scenarios is becoming increasingly robust. But many questions remain, including some big questions. If there was an impact, where would the crater be? This is currently unknown. A team of researchers is currently surveying potential sites (if you speak French, please you can also help).
This research american mineralogist.