OCEANIC CRUST: CHARACTERISTICS AND STRUCTURE - ENVIRONMENT - 2025

The oceanic crust is the part of the earth's crust that is covered by the oceans. This corresponds to two thirds of the surface of the earth and yet it has been less explored than the surface of the moon.

Together with the continental crust, the oceanic crust separates the earth's surface from the mantle, the inner layer of the earth that contains hot, viscous materials. However, these two crusts differ greatly from each other.

The earth's crust is divided into continental crust and oceanic crust.

The oceanic crust averages 7,000 meters thick, while the continental crust averages 35,000. Furthermore, oceanic plates are much younger: they are estimated to be around 180 million years old, while continental plates are around 3.5 billion years old.

The structure of the oceanic crust

In ancient times it was thought that the bottom of the sea was an extensive plain. However, over the years, science has been able to establish that the oceanic crust also has geographic features, just like the continental crust.

At the bottom of the sea you can find mountains, volcanoes and graves. In addition, in some cases there is great seismic and volcanic activity that can be felt even on the continents.

Continental margins and slopes

1. Continental crust. 2. Oceanic crust. 3. Mantle.

Although it is considered that the oceanic crust is that part of the earth's crust that is covered by the ocean, it is necessary to bear in mind that it does not begin exactly on the coasts.

Actually, the first few meters after the coast are also continental crust. The true beginning of the oceanic crust is on a steep slope that can be located a few meters or several kilometers from the coast. These slopes are known as slopes and can reach up to 4,000 meters deep.

The spaces between the coasts and the slopes are known as continental margins. These are not more than 200 meters deep and it is in them where the greatest amount of marine life is found.

Oceanic ridges

The ridges are underwater ridges that occur when the magma present in the mantle rises towards the crust and breaks it. Over the centuries, this movement has generated continuous mountain ranges that exceed 80,000 kilometers in length.

These mountain ranges have fissures at the top through which magma continually flows from the mantle. For this reason, the oceanic crust is constantly renewed, which explains why it is much younger than the continental crust.

Thanks to this continuous volcanic movement, the ridges grow until they leave the surface of the sea, which has generated formations such as the Easter Islands in the Eastern Pacific Ridge and the Galápago Islands in the Oceanic Ridge of Chile.

Abyssal plains

The abyssal plains are the flat areas that lie between the continental slopes and the ocean ridges. Its depth varies between 3,000 and 5,000 meters.

They are covered by a layer of sediments that come from the continental crust and cover the ground completely. For this reason, all the geographical features are hidden, giving a completely flat appearance.

In these depths the water is very cold and the environment is dark due to the remoteness of the sun. These characteristics do not prevent the development of life in the plains, however, the specimens found in these areas have very different physical characteristics from those in the rest of the sea.

The guyots

Guyots are trunk-shaped mountains whose summit is flattened. They are found in the middle of the abyssal plains and reach up to 3,000 meters in height and up to 10,000 in diameter.

Their particular shape occurs when they reach enough height to surface and the waves slowly erode them until they become flat surfaces.

The waves even wear their summit so much that sometimes they are submerged up to 200 meters below the sea surface.

Sea trenches or abyssal trenches

The abyssal trenches are narrow and deep crevices in the seabed, which can be thousands of meters deep.

They are produced by the collision of two tectonic plates, which is why they are usually accompanied by a lot of volcanic and seismic activity that causes large tidal waves and that sometimes is also felt on the continents.

In fact, most of the marine trenches are close to the continental crust, because they occur thanks to the collision of an oceanic plate with a continental plate.

Especially on the western edge of the Pacific Ocean, where the deepest trench on earth is located: the Mariana Trench, more than 11,000 meters deep.

Scientific explorations of the seabed

The oceanic crust has been, throughout history, one of the greatest mysteries of humanity due to the great difficulties involved in diving to the cold and dark depths of the ocean.

That is why science has strived to design new systems to better understand the geography of the seabed and how it originated.

The first attempts to understand the sea floor were quite rudimentary: From 1972 to 1976, scientists aboard HMS Challenger used a 400,000 meter string to submerge it in the ocean and measure where it touched the bottom.

In this way they could have an idea of ​​the depth, but it was necessary to repeat the process in different places to be able to compose a map of the seabed. This activity, of course, was very time consuming and exhausting.

However, this primitive-looking technique allowed us to discover the Mariana Trench, the deepest place on the entire earth's surface.

Today, there are much more sophisticated methods. For example, scientists from Brown University managed to explain the volcanic movement of the ocean ridges thanks to a seismic study carried out in the Gulf of California.

This and other investigations supported by scientific tools such as seismographs and sonars, have allowed human beings to understand the mysteries of the depths better and better, even if it is not possible to immerse themselves in them.

References

1. Challenger Society for Marine Science (SF). The History of the Challenger Expedition. Recovered from: challenger-society.org.uk.
2. Evers, J. (2015). Crust. National Geografic Society. Recovered from: nationalgeographic.org.
3. Extreme Science. (SF). Mid-Ocean Ridges. Recovered from: extremescience.com.
4. Lewis, R. (2009). Oceanic Crust formation is dynamic after all. In: News from Brown. Recovered from: news.brown.edu.
5. The editors of the Encyclopaedia Britannica. (2014). Oceanic Crust. Encyclopaedia Britannica. Recovered from: britannica.com.