In two separate studies, geologists led by Dr Haley Sapers from the University of Western Ontario and Dr Pete Schultz of Brown University have found floral, microbial and organic matter in glass created by ancient asteroid, comet and meteorite impacts. Such glass samples could provide a snapshot of environmental conditions at the time of those impacts and could be a good place to look for signs of ancient life on Mars.
In the first study, published in the journal Geology, Dr Schultz with colleagues found fragments of leaves and preserved organic compounds lodged inside glass created by a several ancient impacts in Argentina.
“The soil of eastern Argentina, south of Buenos Aires, is rife with impact glass created by at least seven different impacts that occurred between 6,000 and 9 million years ago,” Dr Schultz explained.
“One of those impacts, dated to around 3 million years ago, coincides with the disappearance of 35 animal genera.”
“We know these were major impacts because of how far the glass is distributed and how big the chunks are. These glasses are present in different layers of sediment throughout an area about the size of Texas,” he said.
Within glass associated with two of those impacts – one from 3 million years ago and one from 9 million years ago – the team 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,” Dr Schultz said.
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.
To understand how these structures and compounds could have been preserved, the scientists tried to replicate that preservation in the lab.
They mixed pulverized impact glass with fragments of pampas grass leaves and heated the mixture at various temperatures for various amounts of time. The experiments showed that plant material was preserved when the samples were quickly heated to above 1,500 degrees Celsius.
“It appears 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 quickly but the inside takes much longer to cook,” Dr Schultz explained.
In the second study, published also in the journal Geology, Dr Sapers and her colleagues discovered microbes preserved in impact glass.
They analyzed tubular features in hydrothermally altered impact glass from the Ries Impact Structure, Germany, that are remarkably similar to the bioalteration textures observed in volcanic glasses.
Mineral-forming processes cannot easily explain the distribution and shapes of the Ries tubular features; therefore, they suggest the tubules formed by microbes etching their way through the impact glass as they excreted organic acids.
A meteorite impact into a water-rich target such as Earth or Mars has the potential to generate a post-impact hydrothermal system.
Impact structures, especially post-impact hydrothermal systems, represent an understudied habitat with potential relevance to early life and the evolution of early life on Earth.
Understanding the biological significance of impact products such as impact glass on Earth will better inform the search for evidence of life and past life on other terrestrial planets such as Mars.
P.H. Schultz et al. Preserved flora and organics in impact melt breccias. Geology, published online April 15, 2014; doi: 10.1130/G35343.1
H.M. Sapers et al. Enigmatic tubular features in impact glass. Geology, published online April 10, 2014; doi: 10.1130/G35293.1