Why Is Oceanic Crust Denser?

Why Is Oceanic Crust Denser

First of all, you should know that the crust is the outer layer on the surface of the earth. The two significant types of crust we have are the oceanic crust and the continental crust. There are a plethora of discussions concerning the density of the oceanic crust and how it differs from the continental crust.

The question is: why is Oceanic Crust Denser?

Scientists have concluded that the oceanic crust is denser than any other type of crust. One might ask the question why is oceanic crust denser? In this article, we will be examining how the oceanic crust forms and the reasons scientists have concluded that the oceanic crust is denser than the continental crust. There are a lot of reasons that contribute to why the oceanic crust is denser. To explain it in its entirety, we would need to study the oceanic crust, how it comes into existence, and what it constitutes that makes it more impenetrable than the continental crust.

Oceanic Crust

The word “oceanic crust” refers to a flat, compressive, and pure in contrast to continental crust. Also, it is very high in magnesium in comparison to continental crust. The oceanic crust forms as a result of the partial melting of the plates located at the mid-ocean ridges.

Now, after allowing it to cool off, the fraction that remains is the oceanic crust. It is usually about 7km thick or less as per the size of the ridges. Oceanic crust exists when decompression and melting take place below the ribs along the mantle.

The oceanic crust primarily is of basalt. It is singular in its composition with a modular planed texture that exists apart from the ridge spreading percentage. Basalts formed at ridges are called MORB (Mid Ocean Ridge Basalts).

Now, MORBs are different from the regular Basalts placed upon the old oceanic crusts due to volcanic eruptions and volcanism. In our times, we find that all the oceanic crusts present are relatively young.

Geology Of The Oceanic Crust

The oceanic crust makes up for 60% of the earth’s surface and is primarily flat, compressive, and young. The oceanic crust is relatively 12 miles thick, being less than 100 million years as the aged rocks have vanished over time. The oceanic crust is the section of the lithosphere that rises from the ocean basis and comprises mainly of sima or mafic stones. It is slimmer than continental crusts, but it is weightier.

The Continental Crust

The continental crust is the plane of the igneous, sedimentary and metamorphic rocks, which comprises of the surface planes of the various continents in the world. The continental crust is sometimes referred to as the sial due to its chemical composition of materials rich in aluminum and silicates. It is less weighty when drawn in comparison to the oceanic crust, which has a higher chemical composition of magnesium silicate.

Now fluctuations in the velocity of the waves have proven that at a particular depth, there comes a robust peculiar contrast between the upper and lower continental crust. We move on the continental crust, plant our crops, and do our digging on it. Even if some edges may appear to be rough or uneven, the significant parts of the crust comprise of hard rocks.

The vast land areas in our continents have their roots from sedimentary, igneous, and metamorphic rocks. The shield rock is frequently regarded as the oldest rock as it is said to have existed for more than two billion years.

Comparison Between Oceanic Crust And Continental Crust

Various planes of the earth have a variety of materials, all having peculiar attributes attached to them. Factually, density is one of the primary reasons for the formation of the different planes in the earth.

Mathematically, density is known as the mass over volume. So, in essence, thickness could be seen as how weighty a substance is. Its planes are crust, which is lighter in density levitating on the aircraft, which are weightier, such as the mantle.

Different layers of the earth are of materials with different physical properties. Both the Oceanic Crust and the Continental Crust are lighter in weight in comparison to the mantle. It is one of the reasons why the continents situated on planes are with a higher range than the regular ocean floor.

However, continental crust is much lighter in comparison to the oceanic crust, and this makes it possible for it to move higher on the planes. The oceanic and continental crusts, due to their different chemical compositions, have different densities. The continental crust comprises mainly of rocks that are granite in nature or similar to it, while the oceanic crust consists primarily of basalt.

We know that partial melting occurs in the formation of these three substances (mantle, oceanic and continental crusts), and this is the reason they all vary in composition. Now, scientific studies have shown that in the process of melting a rock, some elements will remain in the fold, while others tend to move into the compressed part.

Resulting from this, the foundation formed during the partial melting is less in weight than the original stone. Then, if you also decide to subject that formed rock to the process of partial melting, you get a less dense rock.

The oceanic crust is formed in the mid-ocean ridges when the partial melting takes place in the mantle. While continental crust forms when the rocks are subject to a multiple of partial melting processes, over time, thus, it results in the stones constantly getting depleted in density.

Why Is The Oceanic Crust Denser Than The New Oceanic Crust?

In the ocean, wherever ridges are, tectonic plates tend to drift away, and this causes molten magma to rise. It, in turn, leads to the formation of new oceanic crust. But then as this crust tends to drift away with time, it starts to age, and its temperature reduces. As time goes by, it becomes denser.

Density increased connects to temperature. The reason is that rocks tend to expand in size when subjected to harsh temperatures and contract when allowed to cool. Now, mathematically density is mass divided by volume.

So, this connotes that it is a reduction in volume due to cooling. It leads to an increase in the density of the substance. It is very vital because it illustrates why oceans usually are far away from the ridges and also why the angle in which the plates being altered change when you move from place to place.

Why Is Oceanic Crust Denser Than Continental Crust?

The lithosphere of the ocean, which comprises of the crust and the upper mantle which serves in the function of a “plate” is majorly composed of the elements: basalt (high levels) and gabbro (lower levels).

Boreholes put in place are very useful in the higher planes, and the bottom planes jet seen concluded using the methods of transform fault sampling and also contrasting with mafic igneous rocks

The progression is gotten when the mantle of the granular volcanic rock melts at a considerably guarded rate. It contributes to the basalts having a specific combination of Mid Ridge Basalt Rocks.

On the other hand, the continental lithosphere tends to be more impenetrable due to its high composition of coarse-grained igneous rocks. It comprises a variety of metamorphic rocks, granites, and also sediments compositions. Sedimentary rocks are lesser in density due to their large spaces, and so are granite rocks.

Scientific studies have also proven that the multiple processes that take place in continental rocks to form its texture tend to accept compositions rich in silica readily, and this is one of the reasons for its high granitic composition. For example, partial melting tends to create abundant alkali and silica melts in the process.

Erosion also contributes mainly to the disintegration of the common substances. It occurs before quartz is processed, and this, in turn, leaves sedimentary rocks rich in quartz such as sandstone behind.

Furthermore, pelites have a high composition of aluminum and silica. Then, they will metamorphose from the initial basalt and muddy rocks into migmatites, and laminated rocks like gneisses, which are high in quartz and feldspar. Migmatites comprise primarily of substances that are rich in granite.

Scientific studies have proven that granites are less weighty than basalt. They also show that on surveys, basalts will be seen as positive deviations, whereas the sedimentary constituents will be known as negative deviations.


The oceanic crust is above the mantle of the earth, just like the continental crust. However, they both have different sources, which, in turn, influence the difference in composition, as well as density.

Although the oceanic crust is thinner than the continental crust, it is more significant in density. In providing an answer to the question: why is oceanic crust denser, we need to understand the various processes of heating and melting the continental crust has to be subjected. Thus, due to its chemical composition changes and this, in turn, makes it less dense than the oceanic crust, which undergoes fewer processes.