Your Egypt

[kamar]

June 29, 2006 — Yellow-green glass carved into a beetle-shaped ornament and found on a necklace worn by the ancient King Tutankhamen was created by a meteorite fireball, according to new research.

The carving is known as a scarab, which are ancient Egyptian fertility symbols shaped like dung beetles. In 1999, Italian geologists performed a chemical composition test on Tut’s scarab, which is the centerpiece of a colorful necklace that archaeologist Howard Carter found in King Tut’s Valley of the Kings’ tomb in Luxor.

The geologists determined the scarab was made out of natural desert glass for the king, who reigned from 1333 to 1323 B.C.

Such glass is only found in the Great Sand Sea of the eastern Sahara desert. With a silica content of 98 percent, it is the purest known glass in the world. The desert region, located 500 miles southwest of Cairo, yields this glass in a remote 49.7 by 15.5 rectangular area.

"I think an Egyptian craftsman obtained the glass and worked it into a point or scraper tool," said Mark Boslough, who led a recent study on how the glass formed.

Boslough, an impact physics expert at Sandia National Laboratories in New Mexico, added, "Glass fractures in ways that create sharp, useful shapes, so pieces commonly were used for tools. The glass is also often quite beautiful with interesting colors, so a jewelry maker might have taken an old tool and reworked it into the scarab."

Since most scientists believe heat from a meteorite strike produced Great Sand Sea glass, otherwise known as Libyan Desert glass, Boslough created computer simulations of how that could have happened. He determined a 390-foot-wide asteroid traveling at 12.4 miles per second likely broke up in Earth’s atmosphere around 30 million years ago, when the glass formed.

"The velocity of the impacting object would have produced more energy than a nuclear explosion," he told Discovery Channel News. "It not only would have had nuclear explosive scale, but its energy would all have been concentrated downwards."

According to Boslough, after the meteorite broke up in Earth’s atmosphere, the temperature of the resulting fireball would have been as hot as the sun’s surface.

"Like a blowtorch melting wax, the heat would have melted sand and sandstone into thin layers, which, when cooled, resulted in glass that later was blown into piles across the desert," he said.

Findings were recently presented at a geophysics symposium at the California Institute of Technology in Pasadena. They also will be featured in an upcoming BBC2 television program, "King Tut’s Fireball."

Boslough said additional evidence supports the fireball theory. "Shock minerals," for example, have been found in the same desert. These are minerals, such as quartz, which reveal sheer plane structures under magnification.

Scientists believe such structures resulted from the sudden deformation caused by asteroid and fireball impacts.

Farouk El-Baz, a research professor and director of the Center for Remote Sensing at Boston University, at first was critical of Boslough’s theory. He said, "If this glass is of meteoric origin, there should be a crater of that age."

In March, however, El-Baz himself found remnants of the largest crater in the Saharan desert. It is a double-ringed crater the size of Cairo’s urban region. El-Baz now suggests an extraterrestrial impact that resulted in the crater may have been responsible for the desert glass.

This theory differs from Boslough’s in that it means the asteroid collided with Earth in a sudden hit and did not break into a fireball beforehand.

Boslough countered, "The newly discovered crater is 100 kilometers (around 62 miles) away from where the desert glass is located. Also, why don’t we see this glass elsewhere?"

Boslough and his team are now studying desert glass to determine what trace gases it might contain. The information could help to further explain what happened millions of years ago when the glass formed.

http://dsc.discovery.com/news/2006/06/29/necklace_arc.html?category=archaeology&guid=20060629140000