The Deep Prokaryotic Biosphere Essay

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Only 30 years ago the concept of a vast ecosystem surviving deep underground would seem impossible. At this time the sun was believed to be the root of all of life’s energy systems and therefore without light no life could exist. Microbes had been found deep underground many times but were dismissed as contaminations. In 1980 scientists found hydrothermal vents sustaining a whole ecosystem stemming from extremophiles living from the hot nutrient rich waters, despite the complete absence of light (Gold 1994). A similar discovery was made of a whole ecosystem of invertebrates surviving from chemoautotrophic bacteria in a cave that had been completely sealed from the outside world for more than a million years (Sarbu et al. 1996). The surprising discoveries warped science’s perceptions of the boundaries of life’s existence. After many drill sites found uncontaminated samples of microbes in numbers equivalent to surface populations, hundreds of metres under the ocean floor, the hypothesis of a deep prokaryotic biosphere seemed likely reality (Petersen 2005). The implications of this biosphere are potentially as vast as the biosphere itself. The questions of the biosphere extent, survival, diversity and possible significance in the carbon cycle are now highly debated. This essay will attempt to assess these issues and consider the importance of the deep bacterial biosphere. The extent of the deep prokaryotic biospheres is still widely unknown; the bacteria can dwell in pores of sediment, fractures in hard rock and in fluid inclusion, therefore has the potential to occupy a huge subsurface area (Petersen 2000a). Many estimates suggest the biosphere holds up to 2/3rd of the microbial population (IOPD 2001), and between a 1/10 and 1/3 of the Earth’s entire biomass (IODP 2001, Petersen 2005, Webster et al. 2006, Parkes and Wellsbury 2004, D’Hondt et al 2002). The

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