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Helping store biodata for millions of years.

Asteroid and comet impacts can cause widespread ecological havoc, killing off plants and animals on regional or even global scales, but research from Brown University, Providence, R.I., shows that impacts also can preserve the signatures of ancient life at the time of an impact.

A research team led by geologist Pete Schultz has found fragments of leaves and preserved organic compounds lodged inside glass created by several ancient impacts in Argentina. The material could provide a snapshot of environmental conditions at the time of those impacts. The find also suggests that impact glasses could be a good place to look for signs of ancient life on Mars.

The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. The soil of eastern Argentina, south of Buenos Aires, is rife with impact glass created by at least seven different impacts, according to Schultz. One of those impacts, dated to around 3,000,000 years ago, coincides with the disappearance of 35 animal genera, as reported in the journal Science a few years back.

"We know these were major impacts because of the shocked minerals trapped inside with plant materials," Schultz explains. "These glasses are present in different layers of sediment throughout an area about the size of Texas."

Within glass associated with two of those impacts--one from 3,000,000 years ago and one from 9,000,000 years ago--Schultz and his colleagues found exquisitely preserved plant matter. "These glasses preserve plant morphology from macro features all the way down to the micron scale. It's really remarkable."

The glass samples contain centimeter-size leaf fragments, including intact structures like papillae, tiny bumps that line leaf surfaces. Bundles of vein-like structures found in several samples are very similar to modern pampas grass, a species common to that region of Argentina. Chemical analysis of the samples also revealed the presence of organic hydrocarbons, the chemical signatures of living matter.

It appears, Schultz indicates, that water in the exterior layers of the leaves insulates the inside layers, allowing them to stay intact. "The outside of the leaves takes it for the interior. It's a little like deep frying. The outside fries up rather quickly, but the inside takes much longer to cook."

If impact glass can preserve the signatures of life on Earth, it stands to reason that it could do the same on Mars, Schultz indicates, and the soil conditions in Argentina that contributed to the preservation of samples in this study are not unlike soils found on Mars.

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Title Annotation:Asteroids and Comets; impact glasses
Publication:USA Today (Magazine)
Date:Aug 1, 2015
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