Free-living prokaryotic cells are rarely found in the deep sea and little is known about the potential for life in the vast, low-temperature (<100°C) reservoir of fluids within mid-ocean ridge (MOR) flank and ocean basin crust. Various organism have been observed in MOR vent fluids and in plumes associated with recent volcanic activity, but how far these organism spread across the sea floor has been unclear. In the January 3 Science, James P Cowen and colleagues at the School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA, show that fluids from the aging ocean crust support microbial life (Science, 299:120-123, January 3, 2003).

Cowen et al. used an overpressured 300m-deep borehole fitted with an experimental seal (Circulation Obviation Retrofit Kit – CORK) that could sample sea floor fluids. They observed that the 65°C fluids from 3.5-million-year-old ocean crust support microbial growth and...

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