Space

Microscopic crystals reveal violent aftermath of ancient meteor strike

Aerial view of Meteor Crater in northern Arizona
Aerial view of Meteor Crater in northern Arizona
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Panoramic view of Meteor Crater
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Panoramic view of Meteor Crater
Aerial view of Meteor Crater in northern Arizona
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Aerial view of Meteor Crater in northern Arizona
The crystals used in the recent study were extracted from a rubble pile left by prospectors over a century ago
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The crystals used in the recent study were extracted from a rubble pile left by prospectors over a century ago

An international team of researchers has calculated the cataclysmic conditions created when an asteroid struck northern Arizona roughly 49,000 years ago by analyzing the structure of microscopic crystals known as zircons. The research could be used as a basis to piece together the violent pasts of other solar system bodies including that of Earth's Moon.

Under a powerful microscope, granularzircons appear as a collection of thousands of BB gun-like pellets. Zircons are thought to be created in the minutes directlyfollowing a devastatingly-powerful meteor strike, and capable of maintaining their structure for billions of years.

Panoramic view of Meteor Crater
Panoramic view of Meteor Crater

The impact of the Arizona meteor as itstruck the Earth's surface created temperatures hot enough to melt the quartz grains embedded in the sandstone present in the surrounding crust. Under immense pressure and heat, the quartz formed a glass-like "shock-melted silica," that enveloped thecrystals formed in the event. Samples from the region extracted by prospectors over a century ago were used as the basis for the new study.

The team analyzed the crystals by directing a beam of electrons at 14 zircons, which, upon bouncing off the samples and striking a detector, allowed the researchers to piece together the structure of the unusual crystals. It was found that the orientation of the grains accorded to the level of violent shock that heralded their creation.

A moderate shock would result in what is known as planar cleavage. A more violent impact would cause parts of the crystal structure to orientate in a different direction, and the most cataclysmic of the impacts would transform the zircon into the rare mineral reidite.

The crystals used in the recent study were extracted from a rubble pile left by prospectors over a century ago
The crystals used in the recent study were extracted from a rubble pile left by prospectors over a century ago

The analysis of the crystal structure led the team to estimate that when the Arizonameteor struck the surface, it created a pressure the equivalent of300,000 atmospheres, and temperatures exceeding 2,000º C(3,632º F). Theseconditions were sufficient to cause the zircons to reform theirstructure into the granular formation observed in the samples.

It is hoped that the research will help scientists unravel the history of meteor fragments, and thejourney that they took through space prior to striking our planet, and may even lead to a prediction regarding the frequency of cataclysmic meteor strikes capable of causing an extinction event.Moving forward, team members are applying the technique of examining the structural qualities of the crystals to Moon rock samples obtained during the Apollo era.

Source: University of Wisconsin-Madison

3 comments
cheetahpop
OK, so which of the three crystalline structures did the Arizona crater have? And how was the pressure and temperature determined? Are values for pressure and temperature of the three crystalline structures known? How were they determined? You've caused more questions than answers :(
AtillaDHunn
Did they differentiate between the zircons formed during impact of the asteroid and the obvious zircons created when the asteroid fragment was sheared off it's parent body? Rocks don't occur in free space with only micro gravity.
Don Duncan
I don't see how examining fragments could tell the route (journey) or the frequency that meteors hit. I would like the article to tell what they are looking for that would give that info.