Larry O’Hanlon, Discovery News


March 31, 2008 — A new report of tiny beads of meteor impact glass strewn high in Antarctica’s Transantarctic Mountains may expand a debris field to a tenth of Earth’s surface — despite no sign of the crater which spewed out the molten rock 800,000 years ago.

The accidental discovery of the glass "microtektites" in the high mountains of Antarctica extends what’s called the Australasian tektite strewn field south by nearly 2,000 miles (3,000 kilometers).

The microtektites were found while a team of researchers were searching the exposed rocks atop the Transantarctic Frontier Mountain for more pieces of an unrelated meteorite that disintegrated in the skies there long ago.

"The gradiometer kept on beeping at every fracture of the granitic bedrock surface," recalled Italian researcher Luigi Folco of the Museo Nazionale dell’Antartide, Università di Siena and the Italian Programma Nazionale delle Ricerche in Antartide.

A magnetic gradiometer detects minute changes in magnetic fields caused by rocks containing magnetic minerals. The most likely cause for the beeping was magnetic minerals in volcanic ash from one of the relatively recent volcanoes in the region.

"When we get back to the lab, to our great surprise, we found thousands of micrometeorite and cosmic spherules thus explaining the magnetic signal," Folco told Discovery News.

But they also found glass spheres 0.5 millimeter in diameter with a pale-yellow color, which is unusual for glassy cosmic spherules, which are the debris of meteors melting in Earth’s atmosphere.

The chemical composition of the yellow spheres revealed them to be Earth rocks. That meant there was only one likely way they could have been created — in the heat of an impact, which flung melted rock into space and then rained back down, cooling and solidifying into spheres while in free fall.

The discovery was written up and reported in the April issue of the journal Geology.

The analysis of the microtektites revealed they are similar enough in appearance, composition and age to represent the edges of the Australasian strewnfield, said Folco. That strewnfield already had been found to extend from the Indian Ocean to the Pacific.

"It’s a pretty big strewn field," said tektite pioneer and professor emeritus Bill Glass of the University of Delaware.

Larger tektites from the impact have been found all over Australia and smaller microtektites have been extracted from the bottom of the Indian Ocean, he told Discovery News. But this is the first good evidence that the debris might have been flung even further, he explained.

"You’d think that something that big would be easy to find," said Glass. "It’s a real puzzle."

The most likely location of the hidden crater is somewhere in Indochina, said Glass. One possibility is that the meteor struck down on what is the sea floor today. But 800,000 years ago, an ice age would have lowered the sea level and exposed the seafloor. Since then it could have been buried by marine sediments.

Related Links:

Larry O’Hanlon’s blog: Earth Impacts

Wikipedia: The Australasian strewnfield

Tektites, Microtektites and Impact Glasses

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