Abstract

Summary

• The oceans that cover 70% of the Earth’s surface lie above 3×10⁸ km³ of sediment containing an estimated 3×10²⁹ microbial cells.
• The role played by spores in low-energy sedimentary ecosystems remains an enigma.
• Despite conflicting results from earlier analyses, archaea and bacteria apparently exist in similar abundances within deep-sea sediments.
• Within these sediments, anaerobic metabolisms dominate, especially those in which sulfate reduction and oxidation of organic matter are coupled.
• Modeling proves crucial when trying to connect sedimentary microorganisms to their appropriate geochemical environments.