Microscope image showing tiny tunnels (G) in volcanic glass likely created by microbes. Image by Matthew Nikitczuk

In December 2014, scientists reported that the Curiosity rover has detected belches of methane, which could have been produced by microbes, wafting periodically from the planet’s surface. However, whether this methane is a definitive signature of life remains unclear. What would provide more concrete proof?

Matthew Nikitczuk may have stumbled on one possibility. While conducting fieldwork in ancient lake beds in Oregon, Nikitczuk, a graduate student at Brock University in Ontario, discovered tiny tunnels burrowed into volcanic glass—tunnels that looked biological.

“This is something I’ve never seen before in real life,” Nikitczuk told Eos. “I thought: ‘microbes.’”

Tunneling Through Glass

Nikitczuk, who was looking for Earth analogues for environments on Mars, presented the work in a 16 December poster session at AGU’s annual conference in San Francisco, Calif. He explained that meandering, microscopic tubes within the volcanic glass—some hollow, some filled with minerals—show very characteristic features of trace fossils.

Scientists think that a diagonal fracture in the glass (F) allowed a space for waterborne microbes to creep in and burrow, leaving behind tiny tunnels (G) . Image by Matthew Nikitczuk

Further research revealed that these traces exist all around the Fort Rock volcanic formation in southern Oregon.

As far back as 2 million years ago, lava spilling into a shallow lake cooled and solidified violently in hundreds of continuous explosions as it encountered the water, producing fractured volcanic glass. Over time, water seeped into the lava, flooding the tiny fractures within the glass and bringing heat-loving microbes along with it. The microbes then burrowed farther into the glass, carving the characteristic tubes.

Nikitczuk added that similar-looking traces have been attributed to processes not related to life—such as tiny crystals being pushed through the glass by gas—but his research turned up none of the characteristic nonorganic signs.

Similar structures created by tunneling microbes have been found only in marine environments, Nikitczuk explained. Researchers taking samples of the pillow basalts at mid-ocean ridges have identified similar tube structures; however, Nikitczuk believes that the traces of organisms that he found are from a freshwater lake.

Evidence for a freshwater setting comes from chunks of diatomite—a sedimentary rock built entirely from the silicic skeletons of shelled planktonic organisms called diatoms—found in the dry lake bed. Nikitczuk analyzed the skeletons and determined that they come from a freshwater species.

What Does This Mean for The Search for Life on Mars?

Because Earth-like basaltic rocks and glass are found on Mars, it is possible that similar microscopic tunnels could be discovered as rovers probe the red planet’s surface, said Mariek Schmidt, Nikitczuk’s adviser at Brock University and an active scientist on NASA’s Mars Science Laboratory Mission.

In particular, Gale Crater—where Curiosity is busily roving—is thought to have hosted a lake environment, Schmidt said. A shallower, freshwater lake like the one Nikitczuk analyzed in Fort Rock provides a better analogue for what kinds of environments scientists think existed on Mars, she explained. Thus, a main goal at the moment is to pinpoint the biogenic origins of the tubular structures on Earth, Schmidt said.

“We’ve seen hydrovolcanic rocks on Mars in a number of different locations,” including in Gusev Crater, which was explored by the Spirit rover several years ago, Schmidt added. “I think that this is a really good possible place to find life on Mars, in these kinds of deposits.”

—JoAnna Wendel, Staff Writer

Citation: Wendel, J. (2014), Traces of glass-eating microbes found in ancient lake bed , Eos, 95, doi:10.1029/2014EO020997.

Text © 2014. The authors. CC BY-NC 3.0
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