Antarctic microbes suggest life is possible on Mars
UNIVERSITY OF ARIZONA NEWS RELEASE
Posted: January 15, 2002
Canadian and New Zealand scientists have found living microbes buried deeper than perhaps ever before in Antarctica's ice-free Dry Valleys. They and collaborating planetary scientists at the University of Arizona say new research "opens up the possibility of life on Mars and the possible positions within a soil where it might be found."
The international team is reporting the work in Icarus in the article, "Morphogenesis of Antarctic Paleosols: Martian Analogue."
The scientists have discovered long-lived colonies of insecticidal fungi and a common species of Penicillium bacteria at two sites in two salty soil horizons more than one to three inches (3 to 8 centimeters) beneath Antarctic surface pavement. The cold, xeric Dry Valley soils formed under environmental conditions very like those of past and present Mars, "where similar weathering could occur and possible microbial populations may exist," the researchers said.
"We believe that our field-based investigation of parts of the Antarctic yields valuable information about soils and microbial life that may bear significantly on future manned and unmanned missions to Mars, especially since the martian surface archives an active and varied geologic history similar in many ways to that of Antarctic terrains," they add.
Authors are William C. Mahaney of York University in Ontario, Canada; James M. Dohm and Victor R. Baker of the University of Arizona; Horton E. Newsom of the University of New Mexico; David Malloch of the University of Toronto (who analyzed the microbes); R.G.V. Hancock of the Royal Military College, Ontario, Canada; Iain Campbell of Land and Soil Consultancy Services, Stoke, New Zealand; Doug Sheppard of Geochemical Solutions, Petone, New Zealand; and Mike W. Milner of York University.
The hyper-arid, ultra-cold climate of the Antarctic Dry Valleys comes closer to present-day martian climate than anywhere on Earth. Mean annual temperatures in the Quartermain Mountains, where these microorganisms were found, hover at minus 30 degrees to minus 35 degrees Celsius. Precipitation is practically nil -- equal to less than 10mm (less than four-tenths inch) annually.
Mahaney said that when, in January 1998, he, Campbell and Sheppard ventured into the tills of the Aztec and New Mountain areas, near Taylor Glacier in western Antarctica, they weren't thinking about Mars. Part of Project K-105 in New Zealand's Antarctic Program, they intended to determine the age of paleosols, or ancient soils.
"And we went looking for microbes," Mahaney said.
Mahaney has analyzed microbes in soil in regions ranging from Canada and Wyoming's Wind River Range to Mount Kenya in East Africa. He is about to join Geological Survey of Finland scientists on a full-scale drilling program into more than billion-year-old weathered metamorphic rock in northern Finland that is a possible analogue to a large thrust sheet in the southern hemisphere of Mars. Mahaney performs some laboratory analyses at York University's Geomorphology and Pedology Laboratory, a facility he has directed for 30 years but that is slated for closure starting this year.
Glaciers deposited "tills," or rock debris, at the Aztec and New Mountain areas beginning roughly 23 million years ago, when Antarctic climate was warmer and wetter than at present. Glaciers advanced and retreated repeatedly through time, depositing successive layers of dolerite and sandstone till that weathered and changed chemically when bathed in wind-blown ocean salt and other materials, forming successive soil layers. Each soil layer, as it formed, built up salt and released iron. Salt through time accumulated in the older, lower layers. The glaciers protected rather than eroded the underlying surfaces, preserving the lower horizons in the multistory paleosol profiles, the scientists noted.
Mahaney said they focused on layers they dated using a beryllium-10 isotope dating technique at from 10-to -15 million years old.
"We went to the iron-rich horizons, where we thought we'd find lots of microbes, because microbes need iron for physiological processes," Mahaney said. "And we sampled the lower-down, high-salt horizons, where we thought we would find few microorganisms. We found just the opposite.
"We found microbes in soil with 3,000 ppm salt concentrations. That's like vodka. That's so much salt, temperatures can drop to minus 56 degrees Celsius before there's frost bite. "
Highly concentrated sulphate salts lower the freezing point. Under the right "supercooled" conditions, water remains liquid, noted UA Regents' Professor Victor R. Baker. The availability of liquid water is a problem for microorganisms both in Antarctica and on Mars. "Although these (supercooling) processes are not fully understood on Earth," Baker said, "the fact that they occur in Antarctica shows the possibility that they also might occur on Mars. Indeed, the Mars questions are stimulating exactly this kind of work that will advance our understanding of extreme processes on Earth."
"We also found that these microbe colonies are not just a one-shot occurrence," Mahaney said. "We found abundant, well-formed, long-lived fungi colonies at two sites in two organic-carbon-poor layers between 3 centimeters and 8 centimeters (more than one inch to more than three inches) below the surface pavement.
"The strange thing is, we found several colonies of Beauveria bassiana -- fungi that thrive on insects. The colonies may have been there longer than centuries, maybe millennia, maybe since the last Ice Age -- I have no idea how long. So the question is, what do these well-developed colonies live on?"
Scientists first discovered algae, fungi and bacteria growing inside porous sandstone and surface pavement in the Antarctic Dry Valleys more than 20 years ago. Researchers since have found long-lived algal mats submerged under 10-foot-thick lake ice crust, bacteria living in hot volcanic fumaroles of Mount Erebus, and microorganisms in other Antarctic ecological niches. NASA has long been interested in the Antarctic Dry Valleys as terrain analogous to Mars, and in Earth "extremophiles" -- organisms that grow in the most extreme, severe environments.
But when Mahaney presented a paper at the August 2000 polar science conference in Reykjavik, Iceland, on the weighty implications of finding life in soil horizons in such a hostile environment in many ways analogous to Mars, some dismissed the idea as half crazy, said UA's James Dohm.
He and Baker, however, realized the implications "are extremely important to future unmanned and manned Mars missions that might sample soil horizons to be analyzed for extant life," Dohm said.
They have been collaborating with Mahaney on further research, assimilating the latest analyses of images and information from Mars space missions into the work.
"It appears that tills have been emplaced on Mars under environmental conditions approximately similar to those occurring in the Dry Valleys study site, and that the time scale of 10 million years may apply to both areas," the scientists wrote in Icarus.
And while little so far is known about soils or weathered surfaces on Mars, current thinking is that early Mars' climate was warm and wet, and that throughout its mainly extremely cold, dry climate history, Mars since has been episodically, very briefly, warm and wet, Baker and others conclude. They reported on it in Nature as early as 1991 and as recently as July 12, 2001.
"The glacial climates of Antarctica would have led to glaciers that produced the same kinds of surfaces that were sampled in Antarctica and that we see on Mars today," Baker said.
Dohm, Nathalie Cabrol and Edmon Grin of the NASA Ames Research Center, Jeff Kargel of the U.S. Geological Survey - Flagstaff, and others reported last month at the American Geophysical Union (AGU) meeting on Mars' geologically recent glacial landforms, feature types that Baker also described in his July 2001 Nature insight article.
"Earth-like landscapes which are modified by glaciers, rock glaciers and mudflows are especially pronounced in Mars' southern latitudes, south of 30 degrees," Dohm concludes from a study he conducted with Cabrol and Grin. "Soils may have formed at these southern latitudes, at the tremendously deep (10-kilometer or 6-mile deep) volatile sediment sinks such as Argyre and Hellas impact basins, and at the polar regions," he said.
There is a growing body of geoscientific evidence that suggests Mars' early environment was Earth-like longer than previously believed, he added. "If early Mars was Earth-like, then soils later exposed by faulting, collapse, impact and/or explosion may one day be sampled by a rover," Dohm said he concludes from research in collaboration with Robert Anderson of NASA's Jet Propulsion Laboratory. Explosions would occur if hot magma hits ground water or shallow surface water.
Arizona State University's Paul Knauth reported at the December AGU meeting on the high probability that Mars could produce extremely saline brines, Baker noted. "The evaporation and wind transport of the salts from these brines would readily lead to the types of processes that formed the soil zones in Antarctica," Baker said.
"The water that was mobilized by the changing climates on Mars, implied by the recent water-related landforms would flush these salts into the soil horizons, even for extremely cold mean climate conditions," he said.
Michael Malin and other Mars Global Surveyor scientists reported last month in Science on the fact that martian climate is not stable, but changing even on short time scales, Baker added.
"All these considerations would imply that Mars, like Earth, has climatically sensitive zones that preferentially locate certain kinds of soil development. The past climates that produced certain kinds of soils can then be interpreted, or 'reconstructed,' from the studies of the old soils (paleosols) that formed under those past conditions. " Scientists have used these same kinds of paleosol studies on Earth to study past climates that changed in response to the ice ages.
"Soils and living organisms on Earth are closely associated. In a sense, soil is the 'excited skin of the Earth', as the famous soil scientist Nikiforoff said. If Mars also has soils related to biological process, then they may be related to the history of life on that planet, as well as the history of martian climate," Baker said.