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Research Feature: Study of microbial fossils adds to the “Life on Mars” debate
Posted: March 21, 2006
Researchers have found microscopic tunnels in Martian meteorites that are similar to burrows created by bacteria living in Earth rocks. The discovery was published in the February 2006 edition of Astrobiology and fuels the debate over the existence of life on Mars.
“On Earth, we see a suite of tunnels that are created by bacteria that dissolve and live in volcanic rocks – we found two styles of tunnels in a Martian meteorite that are curiously similar in shape to the tunnels in Earth rocks,” says Martin Fisk, OSU Professor of Marine Geology and Geophysics and lead author on the study.
The team found the tunnels in the Nakhla meteorite, one of the twelve Martian meteorites they studied. Fisk points out that the tunnels are not conclusive evidence of life on Mars. They did not find DNA fragments or other biological material. However, their findings are intriguing and suggest the need for a closer look at other meteorites.
Fisk’s study builds on fifteen years of research into the existence of microbes that can dissolve and live in terrestrial volcanic rocks. The first evidence came from obsidian-like volcanic glass in Iceland. Researchers found tunnels that were about the width of a microbe and began at fractures in the glass where water could penetrate. The systematic patterns and locations of the tunnels suggested that they had a biological origin.
Later, researchers began to recover DNA fragments from within the burrows. Over the last fifteen years, these “trace fossils” have been found in volcanic glass from all over the world – from the sea floor to dry mountain tops in Oregon. The features can endure in rock for millions of years.
“If microbes can live in volcanic glass, we began to wonder if they could also live in olivine and pyroxene,” two minerals common in volcanic rocks. “This is an interesting question in part because the solar system does not contain much glass but it does contain a lot of these other minerals,” says Fisk.
The team looked for and found trace fossils and DNA fragments in olivine from four different terrestrial and marine environments. This is the first documentation that microbes can live in and appear to dissolve other types of volcanic materials besides glass.
Once the team had this evidence, they began to look for similar tunnels in olivine and pyroxene minerals within Martian meteorites. They focused on a group of meteorites that contains clay, a mineral that will only form in the presence of water, one of the essentials for life.
Nakhla is the namesake and most famous meteorite within this group – it was named for the Egyptian site where it landed in 1911. The meteorites were initially linked to Mars because of their distinctive texture, age, and composition. Their Martian origin was clinched in the 1990’s when researchers matched the composition of gas bubbles trapped within them to the unique Martian atmosphere.
The other authors of the study were Radu Popa of Portland State University, Olivia Mason of Oregon State University, Michael Storrie-Lombardi of the Kinohi Institute in Pasadena, California, and Edward Vicenzi of the Smithsonian Institution, Washington, DC. The study was supported by NASA and the National Science Foundation.
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