Limits Of Life On Earth: Are They The Key To Life On Other Planets?

From scalding hot places that rival Dante's Inferno to frigid locations colder than the dark side of the moon, scientists taking part in a $6 million National Science Foundation (NSF) research initiative are searching for life forms on Earth that may provide insight about possible life on other planets. The first NSF awards in this initiative -- which is titled Life in Extreme Environments (LExEn) -- involve more than 20 research projects and some 40 scientists who will look at life in Earth's most extreme habitats.

"Life flourishes on the earth in an incredibly wide range of environments," explains Mike Purdy, coordinator of the NSF initiative. "These environments may be analogous to the harsh conditions that exist now, or have existed, on earth and other planets. The study of microbial life forms and the extreme environments they inhabit can provide new insights into how these organisms adapted to diverse environments, and shed light on the limits within which life can exist."

NSF's directorates of biological sciences; engineering; geosciences; mathematical and physical sciences; and office of polar programs are providing total funding of $6 million to explore the relationships between organisms and the environments in which they exist. A strong emphasis has been placed on environments that are near the extremes of conditions on earth. Funding will also support research about our solar system and beyond, to help identify possible new sites for life beyond earth.

Scientists are studying environments such as the earth's hydrothermal systems, sea ice and ice sheets, anoxic habitats, hypersaline lakes, high altitude or polar deserts, and human-engineered environments such as those created for industrial processes. Projects involve finding techniques for isolating and culturing microbes found in extreme environments, developing methods of studying these microbes in their natural habitats and devising technologies for recovering non-contaminated samples.

• Hyper-arid deserts are among the most extreme environments on earth. The Atacama Desert in Chile, with its rainless regions, is one such hyper-arid desert here on earth. LExEn grantees Frederick Rainey and John Battista of Louisiana State University will investigate the range of microorganisms living in this hyper-arid desert, with the goal of shedding light on the survival of microorganisms in similar extreme environments elsewhere on earth.

• Recent investigations have identified microbial communities in various crustal environments down to 9,200 feet below the earth's surface. Very few microbial samples exist from deep within continental crust, because coring is expensive. But now Tullis Onstott of Princeton University has uncovered a unique opportunity to study microbial communities at depths more than 10,000 feet below the surface: in the gold mines of South Africa. Reconnaissance samples taken from a hole bored into a uranium-rich, gold-bearing mine in South Africa have shown the presence of intact microbial cells. Onstott will examine the relationship between mineralogy and bacteria living in these deep rocks by conducting intensive research at one particular South African gold mine.

• Microorganisms may lie, Lazarus-like, viable but entombed in ice sheets and ice caps of the Tibetan plateau, the South American Andes, and the north and south polar regions. A project by Lonnie Thompson and Ellen Mosely-Thompson, glaciologists at Ohio State University (OSU), and their colleagues will resuscitate microorganisms from ice cores kept at OSU's Byrd Polar Research Center, and use recovered DNA from the organisms to determine relationships to other organisms, as well as abundance and age. The scientists will assess the longevity of the organisms as well as the diversity of tiny life-forms deposited at the same geographical site thousands or even hundreds of thousands of years apart. The researchers hope to uncover extinct genes or gene fragments to compare with modern counterparts.

• What is the telltale signature of past life in extreme environments? The University of Rochester's Ariel Anbar and colleagues will study whether stable isotopes of key metabolic metals fractionate -- and leave their "John Hancock" -- when the metals are taken up and metabolized by microorganisms. If this is the case, the method could be used to identify traces of life in extreme environments where other "biomarkers," or signs of life, cannot be used. The study will focus on copper and zinc isotopes expected to be abundant when these metals are taken up by microbes in a process catalyzed by enzymes, and iron isotopes expected when iron is reduced in reactions mediated by microbes.

• Many regions of the solar system where life is postulated to exist, such as the oceans of Jupiter's moon Europa, are characterized by pressures far greater than those experienced at earth's surface. Relatively little data exists on the nature of barophilic (high-pressure-loving) life forms, or the pressure boundaries within which life may exist. Douglas Bartlett of the Scripps Institution of Oceanography in La Jolla, California, will conduct research on genetic components associated with survival in high-pressure conditions. In his studies, Bartlett will use so-called hyper-barophiles recently obtained from a high-pressure location at the bottom of the Japan Trench, a deep-sea location where pressures reach many tons per square inch.

• How does one study the ancient climate of Mars? James Kasting of Pennsylvania State University hopes to look back through time and see what the paleoclimate on Mars was like. Early Mars appears to have had a warm and wet climate, but existing climate models have been unable to explain this hypothesis. The answer may lie in methane, which, if added to the Martian paleoatmosphere, may have brought the surface temperature above the freezing point of water early in the planet's history. But where would this methane have come from? Such a source could, in principle, have been provided by bacteria living on the surface of early Mars.

• Water, water, everywhere, and how critical to the existence of life, but is it preserved as liquid beneath the icy crust of Charon, Pluto's moon? Until now, researchers have believed that water may be maintained on planetary surfaces through radiative heating from nearby stars. Douglas Lin from the University of California and coworkers will examine whether a layer of water can persist below the surface of a planet's moon, maintained as liquid by tidal interaction between planet and moon. They will analyze such interaction between Pluto and Charon as well as between Uranus and its "satellites."

LIST OF LExEn AWARDS