Earlier this year, we told you about an unusual type of rock known as a quasicrystal, found deep in the Russian mountains in 2010 — the first known naturally occurring quasicrystal. And the most likely origin of that rock was a meteorite from outer space.
Now physicist Paul Steinhardt is back with new evidence that his theory about the origin of that Russian quasicrystal is correct, and that meteorite responsible for its transport likely hit Earth around 15,000 years ago, during the last glacial period.
Those findings just appeared in the journal Reports on Progress in Physics, published by the Institute of Physics in England. It’s one of the most colorful material physics papers I’ve read in recent memory, complete with candid photos of scientists in the field.
Quasicrystals are an unusual type of material first described in the 1980s by Israeli scientist Daniel Schechtman. A quasicrystal has a strange atomic structure that gives it unique properties, falling somewhere between a true crystal and glass.
Schechtman found them quite by accident, while on sabbatical in the US. He was working with rapidly cooled alloys of aluminum and manganese, and noticed an unusual pattern in the electron diffraction pattens they produced.
Schechtman was famously ridiculed for his ideas when he first proposed them, but eventually it appeared in Physical Review Letters. That paper is now one of the ten most cited articles in the history of the journal, sparking a revolution in crystallography and snagging Schechtman the 2011 Nobel Prize in Chemistry.
Most quasicrystals to date — over a hundred different varieties — have been created under carefully controlled conditions in the laboratory. Man made quasicrystals are now used in non-stick frying pans, ball bearings, and razor blades.
But the original theory predicted that quasicrystals should occur naturally, and be as robust and stable as regular crystals. Steinhardt started searching for this elusive object back in 1984 in major museum collections, but came up empty. He resumed the search more than 10 years later, and this time he succeeded.
In 2007, Steinhardt and his cohorts pored over a collection of rocks belonging to Luca Bindi of the University of Florence. One of those specimens,found in the Koryak Mountains, exhibited a quasicrystalline pattern.
A mass spectroscopy analysis revealed unusual ratios of oxygen atoms and their isotopes, matching the ratios typically found inside a certain type of meteorite known as a carbonaceous chondrite. The samples also contained silica, suggesting it had formed under high pressure conditions.
Steinhardt and his colleagues hypothesized that the most likely scenario is that the quasicrystal found in the Koryak Mountains fell to Earth inside a meteorite, outlined in their paper published in the Jan. 2 issue of the Proceedings of the National Academy of Science.
But in order to definitively prove this hypothesis, Steinhardt had to verify that the sample was, indeed, from that region. The paper merely states that the year-long forensic investigation had “more twists and turns than can be recounted here,” while the press release offers tantalizing hints that those twists and turns involved “secret diaries, smugglers, gold prospectors and bears.” (I hereby offer to buy Steinhardt a drink, just to hear his swashbuckling tale of adventure in the way such tales were meant to be told.)
The man who found the sample back in 1979 turned out to be one Valery Kryachko, who was panning for platinum along the clay bed of a tributary of the Khatyrka River. He failed to find platinum but did bring back “a few rocks with metallic phases,” according to the paper. The quasicrystal sample was among them.
So, where there’s one naturally occurring quasicrystal, might there be more? Steinhardt knew this would require an expedition to the place where the original rock was found. Never mind funding, guides, and all the practical details involved in pulling off such an explanation. “Only one person in the world knew the precise spot where the original sample was discovered in 1979, and travel to the autonomous okrug of Chukotka is restricted,” the authors wrote.
But succeed they did, setting off last July with a team of ten scientists, two drivers and cook, crawling across the tundra and into the Koryak Mountains on a pair of slow-moving tractor vehicles. It took four days just to get there, and the effort seems to have been worth the trek.
Steinhardt and his colleagues collected more samples, which contained more naturally occurring quasicrystals. They were also able to verify that the local terrestrial environment didn’t have the kind of extreme conditions that would have been necessary to produce such quasicrystals, significantly bolstering Steinhardt’s case that they arrived here via meteorite. Based on sediment samples, the researchers peg the likely date of that impact at around 15,000 years ago.
“The fact that the expedition found more material in the same location that we had spent years to track down is a tremendous confirmation of the whole story,” Steinhardt said via press release.
Images: (top) Courtesy of Paul Steinhardt, Princeton University. (bottom) Atomic model of fivefold icosahedral-Al-Pd-Mn quasicrystal surface. Credit: J.W. Evans, The Ames Laboratory, US Department of Energy. Public domain.