For more than three billion years, microorganisms have served as engines of Earth’s biosphere, driving essential biogeochemical cycles that shape planetary habitability. Exploration of the sea over the last 40 years has resulted in astounding discoveries about the extent and diversity of life in the deep ocean, pushing our understanding of the intimate connections between the biosphere and geosphere to the extremes, including the discovery of chemosynthetic ecosystems at hydrothermal vents and active microbes buried in sediments, kilometers beneath the seafloor. In fact, the global ocean comprises Earth’s biggest microbiome, with at least half of the ocean’s microbial biomass occurring beneath the ocean floor. Read more ..