The fascinating creation of Libyan desert glass (LDG) has sparked a significant debate in the field of planetary science. From discussions of lightning and unusual geological processes to theories about volcanoes on the Moon, scholars have proposed various sources for this mysterious glass. Over the past 25 years, experts have primarily focused on two scenarios: LDG was either formed by a meteor colliding with the desert or by a meteorite exploding high up in the atmosphere, known as an airburst. Fresh findings now suggest that the former assumption is most likely the correct explanation.
Glass is typically produced by heating sand, so most hypotheses involve a considerable amount of energy impacting the desert sand located between Egypt and Libya. Both meteorite impacts and airbursts have the potential to generate the high temperatures required to transform sand into glass through a process of high-temperature fusion.
The lead author of the study, Dr. Elizaveta Kovaleva from the University of the Western Cape, stated, “The primary objective of our research was to differentiate between an airburst, similar to those experienced over Chelyabinsk or Tunguska, and a meteorite impact on the surface.”
Tutankhamun’s pectoral features a scarab carved from Libyan desert glass.
The researchers embarked on a quest to uncover evidence that would delineate one scenario from the other. An essential distinction exists between an impact and an airburst. While airbursts can generate high temperatures and shock waves in the air, they are unable to exert sufficient pressure into the ground to create shocked minerals. As a result, the researchers scrutinized the detailed composition of the glass.
An international team of researchers used transmission electron microscopy to examine the organization of minerals within the LDG. They discovered tiny crystals of zircon oxides, with particular attention paid to their different arrangements under various conditions.
One of the observed configurations is known as cubic zirconia. This arrangement, typically associated with jewelry, requires high temperatures ranging from 2,250 to 2,700 degrees Celsius (4,082 to 4,892 degrees Fahrenheit) to form. However, the researchers noted mineral melts indicating even higher temperatures during their observations.
Temperature alone does not suffice for distinguishing between an impact and an airburst. Another configuration of zirconia identified in the glass requires both high heat and very intense pressure, approximately 130,000 atmospheres. If these minerals crystallized under those conditions, the most plausible explanation would be a meteorite impact.
“These are very minute crystalline particles that exclusively crystallize under extremely high pressures. Such high pressures can only be generated within the Earth’s crust following meteorite impacts, and they were preserved within the LDG due to their minuteness,” explained Dr. Kovaleva.
While evidence supporting the impact scenario is mounting, numerous questions remain, notably the absence of a visible crater from the impact. At present, this remains unknown. A team of researchers is currently surveying potential sites, and for those proficient in French, you can assist as well.
The study has been published in American Mineralogist.
