When an asteroid plows into the Earth, it destroys pretty much everything in its path. But new research has shown that glass created during a searing asteroid impact can actually trap microscopic signs of life for millions of years, providing scientists with a snapshot of the biology in the area just before and after the strike.
At a site in Argentina, researchers found bits of plant material embedded in a type of glass formed during meteorite strikes. Because the glass contains insight into the flora in the area just before the crash -- similar to how amber traps and preserves plants and bugs -- the researchers are calling it "impact amber." Meanwhile, a separate group has spotted bizarre tubular features in meteorite-created glass at a crater in Germany that tells them about a microbial ecosystem that lived in the residual heat generated by an asteroid hitting the ground. Both results could help us in the search for life on other worlds.
In Argentina, scientists looked at the glass produced by seven different asteroid impacts occurring between 6,000 and 9.2 million years ago. “We kept seeing these things embedded in the glass, some of which looked like scratch marks and others that looked like twigs,” said planetary scientist Peter Schultz of Brown University, co-author of one of the two new papers that appeared April 15 in Geology.
Though they initially thought the marks might be some kind of new crystal, Schultz and his colleagues were able to identify biological structures up to an inch long, including veins, fibers, and bumps similar to those seen on modern day pampas grass. Getting a closer peek with scanning electron microscopes, they saw preserved cells and, using a spectrometer, they also found polycyclic aromatic hydrocarbons (PAHs), carbon structures that would have once been part of chlorophyll and other large organic molecules.
When an asteroid hits the ground, it can generate temperatures of many thousands of degrees, melting rocks, and vaporizing and killing everything nearby. To find out how biological structures survived such heat, the team took bits of pampas grass and mixed it with pulverized impact glass. They found that if this mixture was heated up extremely quickly above 2,700 degrees Fahrenheit, the grass was preserved. As it turns out, water in the exterior layers of the grass managed to absorb most of the heat as those layers burned away, protecting interior structures from too much damage in a process that Schultz likened to deep-frying.
The specific area in Argentina where the asteroids hit may have also played a part in preserving the plants. Much of the ground in the region is covered in a type of sediment known as loess, formed when wind-blown dust accumulates in layers. Schultz used NASA’s vertical gun range to fire tiny pellets into sand and simulate the asteroid strikes to figure out a plausible scenario for the impact amber’s creation. Because it heats up easily, loess readily forms impact glass that would have trapped biological structures. Pieces of molten glass could have also been flung from an impact crater “like big balls of molasses,” said Schultz. These globs could have rolled through the dusty plains, further sealing and preserving the plant materials.
In addition to ensnaring living things that existed just before they hit, it appears asteroids may also be able to nurture a strange form of life just after they strike. At a 14.5-million-year-old meteor impact crater in Germany, a different team of researchers has spotted structures formed by microbes that lived in near-boiling water and ate glass.
While looking closely at impact glass from the German crater, scientists noticed enigmatic tubular features that curved and spiraled throughout the material. Though these structures were originally thought to be some sort of strange crystal, they displayed many non-crystalline qualities.
“A lot of them have segments, they form these beautiful coils, they branch or bifurcate, and they seem to avoid each other,” said astrobiologist Haley Sapers of the University of Western Ontario in Canada, co-author of the second Geology paper.
Sapers and her colleagues looked at the features with a scanning electron microscope and found that they were hollow and all seemed molded from the same shape. They also discovered within the structures high concentrations of organic carbon, and saw little organic material outside of them. They posit that the tubular features were created by tiny bacteria living in the aftermath of an asteroid impact. Similar structures are thought to have been spotted in other ancient glasses found on the bottom of the ocean.
“There are basically microbial footprints,” said Sapers. “They show microbes tunneling through impact glass.”
The team thinks that after the asteroid impact, the area would have been sterilized. But residual heat could have kept the region at a temperature of around 150 degrees Fahrenheit for as long as 10,000 years. The impact glass shows evidence of being underwater for long periods of time, suggesting that the crater could have formed a hot spring ecosystem much like modern-day places such as Yellowstone. Though most organisms couldn’t stand the extremely hot water, some microbes may have colonized the site, feeding off the glass.
Both of the findings provide scientists with an unexpected place to look for evidence of ancient life: the bottom of a once-smoking crater. The teams think both results could aid in the search for evidence of life on other planets, opening up potential targets for exploration on Mars for instance. The Red Planet is covered both in craters and dusty loess-like material that could form impact glass. Such glasses have never been a high priority in the search for fossil evidence on Mars but this new work could make researchers reconsider.
Though the biological crater-impact findings are only on the order of tens of millions of years old—a mere geological minute ago—“it’s conceivable that things are better preserved in ancient Mars rocks than ancient Earth rocks,” said planetary scientist Richard Leveille of McGill University, who was not involved in the recent research but who is a member of NASA's Curiosity rover science team.
The Red Planet had less tectonic activity than our own, meaning that ancient rocks have probably not been subducted and recycled in the planet's interior. These old rocks could sit much closer to the surface. Rovers might one day collect impact glass and try to test it for structures similar to those observed in the recent research. But “proving these things on Mars will be a real challenge,” said Leveille.
Even the most capable machine on Mars, the Curiosity rover, lacks the sophisticated laboratory equipment used to discover the plant and microbe preserves in these two papers. A much more complex and expensive sample return mission will probably necessary to achieve results like the ones in this recent work. __
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