The Soft Seabed

The seafloor’s soft bottom consists of lithogenic and biogenic sediments—sand and dust from weathered rock and the remains of animals and plants, respectively—that descend from the upper water layers. Indigestible matter like the hulls of unicellular animals such as foraminifera and radiolarians, as well as microscopic algae, sinks to the seabed and accumulates over the eons as silt.