The Enigma of the Desert Glass Solved by Meteorite Collision

The impact took place 200,000 years ago

By Stefan Anitei on December 27th, 2006 16:19 GMT
Scientists found in 1987 strange specimens of natural glass (known locally as Dakhla glass) in the western Egyptian desert and have been puzzled by the origins of those stones.

Some suggested that the glass might have been the product of vegetation burning or lightening strikes.

But recent chemical analysis pointed that this glass was created at such a high temperature that it can only be the product of a meteorite slamming into Earth between 100,000 and 200,000 years ago.

At the time of the impact, the Dakhla Oasis was a typical African savanna, inhabited by early human species, as the archaeological evidence shows.

"This meteorite event would have been catastrophic for all living things," said Maxine Kleindienst, an anthropologist at the University of Toronto in Canada.

"Even a relatively small impact would have exterminated all life for [several] miles."

The glass contains strands of molten quartz, a clear sign of meteorite impacts.

"We can now say for definite that they were caused by a meteorite impact," said Gordon Osinski, a geologist at the Canadian Space Agency in Saint-Hubert.

The glass deposits were spread over tens of kilometers, with no signs of an impact crater, suggesting a massive event.

"Usually from an impact like this, we should have a crater at least a kilometer [0.6 mile] across," Osinski said.

No crater means that the large meteorite may have split off upon entering Earth's atmosphere.

"In an air burst like that, contents of the explosion continue to travel downward … providing a gas pulse across the [Earth's] surface that could vitrify sediments," said Albert Haldemann, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, California.

Something similar passed with the Tunguska meteorite that fell in 1908 in Siberia and did not leave any crater.
At the impact time, there was a large lake in the area.

"If there was an impact at the surface and it happened to hit the lake, it wouldn't be surprising if the [crater] was filled in," Haldemann said.

"Did the event boil the entire lake away, or did it just cause a really big wave to go across the lake? Maybe we can figure that out from the sediments."

Human stone tools including spears and scrapers prove that the area was inhabited from about 200,000 to 30,000 years ago.

Human habitation evidence was found in the soil layers below and above the glass.

"Calculations at Meteor Crater [in Arizona] give some idea of what the effect of a [relatively small] impact would be," she said.

"Life forms are killed or seriously injured for many tens of kilometers away from the impact."

"If this event happened during a humid period, the area might have been ecologically repopulated fairly quickly from surrounding areas," she added.

"But if it happened during a dry period, it might have taken a considerable period for life to be re-established in the oasis region."

The meteorite events remember us the interconnectedness between Earth and the solar system.

"We already know the environment of the whole Earth is tied together," said Haldemann.

"What we've been learning more and more in the last 20 years or so is that we're also tied to the solar system as a whole over longer time periods and that this interaction tends to be punctuated by these catastrophic events."

"Here we have evidence in the [Early Stone Age] records that this kind of thing can really happen to us."