Marine sediment

Tiny bits of sand and dirt sit on the ocean floor.

This pile is called sediment.

Some bits come from the land. Rivers carry them to the sea. Wind and ice also move them.

Other bits come from sea life. Tiny creatures make shells. When they die, the shells sink. They pile up on the bottom.

Volcanoes can also add to the pile. Some bits even fall from space! These come from rocks called meteorites.

This layer can be very thick. It can even turn into rock. It gives small sea animals a place to live.

Tiny bits of rock and shell sit on the ocean floor. This pile is called marine sediment.

Most of the seafloor is covered in it. Some layers are thin. Other layers are tens of kilometers thick.

Where does it come from? Much of it is lithogenous. This means it comes from land. Rivers carry sand and clay to the sea. Wind carries dust. Glaciers also move rocks into the water.

Other bits are biogenous. These come from living things. Tiny sea creatures make shells. When they die, the shells sink. They form thick layers called oozes.

Some oozes are made of silica. These come from tiny organisms like diatoms. Others are made of carbonate. These shells might dissolve in very deep water.

Some sediment comes from volcanoes. Other bits fall from space on meteorites. Over a long time, deep sediment can turn into rock. This is called lithification. These layers help us learn about the past. They tell us about old climates and sea life.

The ocean floor is not just empty space. Most of it is covered by a thick layer of marine sediment.

This material is made of tiny, solid particles that settle over time. These layers can be very thin or very thick. Some areas have only a few millimeters of sediment. Other places have layers that are tens of kilometers deep. Most of the seafloor is covered by this material. The only places that are not are near mid-ocean ridges. At those ridges, the volcanic rock is still quite young.

There are four main ways these sediments form. First, lithogenous sediment comes from the land. Rivers carry about 90% of this material into the sea. Wind can also blow dust and sand across the water. Glaciers move rocks and even large boulders into the ocean. Second, biogenous sediment comes from living things. Tiny organisms like diatoms make shells out of silica. Other creatures make shells out of carbonate. When they die, their remains sink to the bottom. These thick layers of shells are called oozes.

Third, hydrogenous sediment forms from chemical reactions in the water. This happens when materials dissolve in the water and then turn into solids. These are called precipitates. Fourth, cosmogenous sediment comes from outer space. It arrives on Earth through meteorites or as it filters through the air.

These different sources make the seafloor very diverse. You can find different types of material depending on where you look. For example, clay is found in the deepest parts of the ocean. Near the coast, you might find sand, silt, or even pebbles.

Scientists use special tools to study these layers. They look at the grain size of the particles. They use the Wentworth scale to name these sizes. This scale ranges from tiny clay to huge boulders.

They also look at how well-sorted the sediment is. Well-sorted sediment has particles that are all about the same size. Poorly sorted sediment has many different sizes mixed together. They even look at how round the grains are. Over time, water rubs the edges off the particles. This makes them smoother and more mature.

These sediments are like a history book for our planet. They can be very old. Near the surface, the sediment is loose and soft. At depths of hundreds or thousands of meters, it becomes lithified. This means it turns into solid rock.

These rocks hold many secrets. Their fossils tell us about past climates and ocean patterns. They also show us when major extinctions happened. By studying the seafloor, we learn how the Earth has changed over time.

Marine sediment refers to the various deposits of insoluble particles that accumulate on the seafloor. These materials cover most of the ocean floor, except for areas near mid-ocean ridges where volcanic rock is still relatively young.

The thickness of these layers is highly variable. In some regions, the sediment is only a few millimeters deep. In other areas, it can reach thicknesses of several tens of kilometers. This material is essential because it provides a habitat for many marine organisms, particularly microorganisms.

It also serves as a geological record of our planet's history.

Sediment formation follows several distinct pathways based on its origin. The first type is lithogenous sediment, also called terrigenous sediment. This material is derived from preexisting rocks on land. It reaches the ocean through several mechanisms. Rivers are a major contributor, providing about 90% of all lithogenous sediment via discharge. Wind can transport fine dust and sand thousands of kilometers across the sea. Glaciers also play a role by grinding rocks and carrying them to the ocean. When glaciers melt or break apart, they release these particles through a process called ice rafting.

Another major category is biogenous sediment, which comes from living organisms. Many marine creatures, such as plankton, build shells or skeletons called tests. Some organisms, like foraminifera, create these tests from carbonate minerals like calcite. Others, such as diatoms and radiolaria, use silica to build their structures. When these organisms die, their remains sink through the water column. If they accumulate in large amounts, they form thick layers known as oozes.

These biogenous deposits are common in specific regions, such as the equatorial Pacific or the south polar regions.

Chemical and extraterrestrial processes also contribute to the seafloor. Hydrogenous sediments form through chemical precipitation. This occurs when dissolved materials in the seawater undergo a reaction and turn into solid particles. For example, iron and manganese nodules can form directly from ocean-bottom water. Finally, cosmogenous sediments arrive from outer space. These particles enter the ocean via meteorites or by filtering through the Earth's atmosphere.

These diverse sources ensure that the composition of the seafloor is highly variable.

The depth of the ocean significantly affects which sediments can exist. Carbonate sediments are widely distributed in equatorial and mid-latitude regions. However, calcite becomes more soluble as depth and pressure increase. At a specific depth known as the carbonate compensation depth, carbonate fragments dissolve completely. This depth is typically around 4,000 meters, though it varies with temperature and latitude. Consequently, carbonate oozes are absent from the deepest parts of the ocean.

In these deep areas, fine clay particles become the dominant sediment type.

Scientists classify marine sediment using specific physical properties. One method is measuring grain size using the Wentworth scale. This scale ranges from tiny clay particles, which are less than 0.004 mm, to large boulders over 256 mm.

Another property is sorting, which describes how uniform the particle sizes are. Well-sorted sediments, like beach sand, have particles of similar size. Poorly sorted sediments contain a wide range of sizes. Scientists also look at maturity, which refers to how long particles have been transported. Mature sediments often have rounder grains due to abrasion and higher quartz content because quartz is very resistant to wear.

The seafloor is part of a massive, ongoing geological cycle. The deep ocean floor spreads away from mid-ocean ridges. Eventually, the accumulated sediment is pulled into the Earth's molten interior through subduction. In turn, new material returns to the surface via lava flows and hydrothermal vents.

This continuous movement helps regulate the Earth's systems. By studying these layers, researchers can uncover information about past climates, ocean circulation patterns, and the timing of major mass extinctions. The sediments act as a deep archive for the history of life and the movement of tectonic plates.