Seafloor sediments host diverse microbial ecosystems As much as 70 percent of the microbes alive on Earth reside on and just below the ocean floor, two new studies suggest. The seafloor was once thought to be a barren expanse of muck dotted with an occasional thriving ecosystem near a hydrothermal vent. More recently, however, scientists have discovered that microorganisms can fuel their metabolisms by taking advantage of the chemical energy stored in various minerals, including those that make up the ocean crust.