19 November 2004
Mars-like Soils Can Harbor Life
by Kate Melville
Chile's Atacama desert gets rain perhaps once a decade and scientists believed that the driest Atacama soils were sterile. But a team of Arizona scientists now report that microbial life lurks beneath the arid surface of this absolute desert. "We found life, we can culture it, and we can extract and look at its DNA," said Raina Maier from the University of Arizona.
Her team's work, to be published in Science, contradicts last year's widely reported study that asserted the "Mars-like soils" of the Atacama's core were the equivalent of the "dry limit of microbial life". The project began not as a search for current life but rather as an attempt to peer into the past and reconstruct the history of the region's plant communities. Co-researchers Julio Betancourt and Jay Quade have been conducting research in the Atacama for the past seven years. Some parts of the Atacama have vegetation, but the absolute desert of the Atacama's core - an area Betancourt describes as "just dirt and rocks" - has none.
To figure out whether the area had ever been vegetated, Quade and Betancourt had to search the soil for biologically produced minerals such as carbonates. To rule out the possibility that such soil minerals were being produced by present-day microorganisms, the two geoscientists teamed up with UA environmental microbiologist Maier. In 2002, the researchers collected sterile soil samples along a 200-kilometer transect that ran from an elevation of 4,500 meters to sea level. The geoscientists brought their desert soil back to Maier's lab, where her team wetted the soil samples with sterile water, let them sit for 10 days, and then grew bacteria from them. "We brought 'em back alive, it turns out," Betancourt said. The other researchers who had tested soil from the Atacama had looked for life only down to the depth of four inches. "Don't just scratch the surface," said Quade.
Maier and her team have not yet identified the bacteria that come from the extremely arid environment of the Atacama's core but Maier said they are unusual. "As a microbiologist, I am interested in how these microbial communities evolve and respond. Can we discover new microbial activities in such extreme environments? Are those activities something we can exploit?" Maier suspects the microbes may persist in a state of suspended animation during the Atacama Desert's multi-decadal dry spells.
The team's findings suggest that how researchers look for life on Mars may affect whether life is found on the Red Planet. Saying that Mars researchers are most likely looking for a needle in a very large haystack, Maier said, "If you aren't very careful about your Mars protocol, you could miss life that's there." Peter H. Smith, the UA planetary scientist who is the principal investigator for the upcoming Phoenix mission to Mars, said, "Scientists on the Phoenix Mission suspect that there are regions on Mars, arid like the Atacama Desert in Chile, that are conducive to microbial life." He added, "We will attempt an experiment similar to Maier's group on Mars during the summer of 2008."