DEEP BACTERIAL BIOSPHERE IN PACIFIC-OCEAN SEDIMENTS

ALTHOUGH around 70% of the Earth's surface is marine, little is known about the microbiology of underlying sediments, which can be more than a kilometre deep(1). Selective degradation of organic matter within s ediments over geological time profoundly affects the chemical composit ion of the ocean and atmosphere(2). Microbial processes have a fundame ntal role in surface sediments(3,4), but despite geochemical evidence( 5), their significance in deeper sediments has not been established(6) . Here we report the discovery of viable sediment bacterial population s at five Pacific Ocean sites to depths >500 m. Bacterial distribution s and activities are commensurate,vith geochemical changes. Bacterial profiles with depth are remarkably consistent, and deviations can be l inked to specific environmental factors. The rate of decline in these populations indicates that bacteria are present to even greater depths . These bacteria, some of which are unique, must have a profound effec t on deep-sediment diagenetic processes, and their presence considerab ly extends the biosphere.