The seafloor is a vast, shifting archive of Earth's history and cosmic debris.

Nature · Published 3 October 2026 Swipe more like this →

In short: Marine sediment is far more than just mud. It is a complex accumulation of rock, volcanic ash, skeletal remains of ancient organisms, and even extraterrestrial material like meteorites. These layers blanket the ocean floor, acting as a dynamic record of our planet's geological evolution and its changing climate over millions of years.

Marine sediment consists of insoluble materials that settle on the seafloor, originating from land-based sources like rivers, wind, and ice, as well as submarine volcanism and chemical precipitation. Near continents, these deposits are often terrigenous, characterized by sand, silt, and clay. In contrast, the deep ocean floor is dominated by pelagic sediments, which accumulate slowly and are primarily composed of biogenic constituents—the skeletal remains of marine life such as diatoms, radiolarians, and foraminiferans. When these biological remains exceed 30 percent of the total volume, the sediment is classified as an ooze, named after the dominant organism.

The movement of these materials is often dramatic. Near continental shelves, turbidity currents—dense, sediment-laden masses triggered by earthquakes—can flow down submarine canyons at speeds of several tens of kilometres per hour. These currents deposit turbidites, which often exhibit a systematic change in grain size from coarse at the bottom to fine at the top. Because these currents move rapidly, the individual grains often retain characteristics from their point of origin, unlike the slower-accumulating pelagic sediments that settle far from land.

The study of these deposits has fundamentally reshaped our understanding of the Earth. Since 1968, the deep-sea drilling vessel Glomar Challenger recovered core samples that provided critical evidence for the seafloor-spreading hypothesis. Researchers discovered that no deep-sea sediments are older than 150,000,000 years, revealing that the seafloor is geologically young. As oceanic crust forms at mid-ocean ridges and moves outward, it carries these sedimentary layers with it until they are eventually destroyed at oceanic trenches. This continuous cycle ensures that the seafloor is constantly renewed, while the preserved fossils within the sediment offer a detailed timeline of past extinctions, plate tectonics, and ocean circulation patterns.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Some of the mud on the ocean floor fell from outer space
• The ocean floor is blanketed in the skeletal remains of microscopic, glass-like organisms
• Underwater avalanches of sediment are the primary architects of the deep ocean floor
• How underwater avalanches of sand and mud shape the deep ocean floor
• Over half of Earth's surface is dark, flat seafloor few people have seen
• Fire ice: The strange, cage-like crystals hiding beneath our ocean floors
• Lakes are not just puddles; they are complex, layered machines that breathe with the seasons.
• The ocean is not a static pool but a complex, stratified, moving machine.
• The intertidal zone is a high-stakes arena where land and sea constantly collide.
• The ocean is not flat: mapping the hidden hills and valleys of our seas
• The hadal zone is Earth's final frontier, hidden in the deepest ocean trenches.
• The ocean is a massive heat engine, and its temperature is hitting record highs.

More in Water · More in Nature · Latest · A–Z · All topics