《《Microbial origin of methane in ice cores》.pdf

Microbial origin of excess methane in glacial ice and implications for life on Mars † †‡ H. C. Tung*, N. E. Bramall , and P. B. Price Departments of *Environmental Science, Policy, and Management and †Physics, University of California, Berkeley, CA 94720 Contributed by P. B. Price, August 31, 2005 Methane trapped in the 3,053-m-deep Greenland Ice Sheet Project Bacteria and archaea have been found in all subfreezing 2 ice core provides an important record of millennial-scale climate terrestrial environments (2–6). Studies of terrestrial psychro- change over the last 110,000 yr. However, at several depths in the philes and psychrotrophs have involved extraction and exami- lowest 90 m of the ice core, the methane concentration is up to an nation of cells from cold water, ice, or permafrost. Studies of order of magnitude higher than at other depths. At those depths microbial life in cold environments on Earth help us to under- we have discovered methanogenic archaea, the in situ metabolism stand how life could have arisen on cold planets such as Mars. of which accounts for the excess methane. The total concentration Instruments to look for chemical evidence of extant or extinct of all types of microbes we measured with direct counts of life in the Martian subsurface are being developed for future Syto-23-stained cells tracks the excess of methanogens that we missions, and Mars samples eventually will be returned to Earth identified by their F420 autofluorescence and provides indepen- for study. Ideally, remote selection of such samples can be dent evidence for anomalous layers. The metabolic rate we esti- expedited by equipping rovers with instr