AAS 201st Meeting, January, 2003
Session 70. The Biology of Astrobiology for Astronomers II
Special, Tuesday, January 7, 2003, 2:00-3:30pm, 618-619

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[70.02] The Limits of Life on Earth

J. W. Deming (School of Oceanography/Astrobiology Program, U. Washington)

Microorganisms inhabit environments more extreme than those of higher organisms, and recent research results are vastly expanding our notion of where life may occur elsewhere in the Universe. These "extremophiles" have evolved to handle conditions previously thought impossible for life. The temperature limits of microbial activity currently stand at -20C in Arctic winter sea-ice brines (psychrophiles) and 113C in the pressurized water emerging from seafloor hydrothermal vents (hyperthermophiles). Moreover, indirect evidence exists that this upper temperature limit may be significantly higher. The pressure limits on microbial activity are unknown, since some cultures (barophiles) continue to metabolize at the highest pressures tested (1100 atm, mimicking the deepest trench in the ocean). Recent studies have extended the pressure for metabolic activity in bacteria to greater than 10,000 atm. Certain types of microorganisms (acidophiles) are also known to grow in the extreme acidic conditions (pH = 0) found in some geothermal vents and mine waste sites, as well as others (alkalophiles) in alkaline environments such as high-carbonate lakes (pH = 12). Other microbes (halophiles) have evolved to grow in saturated brines (5 Molar NaCl), with heavy metals (e.g., 5mMolar Cd), and under levels of DNA-damaging radiation up to 6000 rad/hr and 15 Mrad total.


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Bulletin of the American Astronomical Society, 34, #4
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