Oceanic Crust and Continental Crust: The Difference
The Earth's crust is the outermost layer of our planet, composed of solid rock. The Earth's crust varies in thickness from about 5 to 70 kilometers. It's relatively thin compared to the Earth's mantle and core, but it's the part we interact with directly. The crust is divided into two main types: continental crust, which is thicker and less dense, and oceanic crust, which is thinner and denser.
How is oceanic crust different from continental crust
Continental crust
Continental crust varies between 10 and 43 miles in thickness depending on where it is found. Continental crust tends to be much older than the oceanic kind, and rocks found on this kind of crust are often the oldest in the world. Examples of such rocks are those in Quebec, Canada which are estimated to be about 4 billion years old.
Composition: Continental crust is mainly composed of granite, gneiss, and other felsic rocks, which are rich in silica (SiO₂) and aluminum (Al). These rocks are lighter and less dense than the rocks of oceanic crust.
Thickness: The continental crust is much thicker than oceanic crust, ranging from 20 to 70 kilometers in thickness.
Formation: It is primarily formed through mountain-building processes over millions of years, involving the collisions of tectonic plates and the subsequent melting and cooling of rock.
Features: Characterized by mountain ranges, plateaus, and cratons (ancient, stable regions of continental crust).
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Thicknesses of Earth's crust, showing the thinner oceanic crust at 6-10 km and the thicker continental crust up to 70 km under mountains. |
Oceanic Crust
Oceanic crust is found under oceans, and it is about four miles thick in most places. A feature unique to oceanic crust is that there are areas known as mid-ocean ridges where oceanic crust is still being created. Magma shoots up through gaps in the ocean’s floor here. As it cools, it hardens into new rock, which forms brand new segments of oceanic crust. Since oceanic crust is heavier than continental crust, it is constantly sinking and moving under continental crust.
Composition: Oceanic crust is Mainly composed of basalt, which is a mafic rock rich in iron (Fe) and magnesium (Mg). These rocks are denser than the rocks of continental crust.
Thickness: Oceanic crust is much thinner than continental crust, typically measuring only 6 to 10 kilometers thick.
Formation: Oceanic crust forms continuously at mid-ocean ridges through the upwelling of molten rock from the mantle.
Features: Characterized by oceanic trenches, volcanic islands, and seamounts.
Age: The oceanic crust is relatively young, with the oldest parts being about 200 million years old.
Oceanic and Continental Crust Comparison
Composition
Oceanic crust is dominated by mafic and ultramafic intrusive igneous rocks whereas continental rocks are dominated by granitic (felsic) intrusive igneous rocks. The mantle, oceanic crust, and continental crust all have different compositions due to a process called partial melting.
Formation
The differences between oceanic crust and continental crust are due to the different ways in which they are formed. Oceanic crust is formed from magma that rises from the mantle and cools at the ocean floor. Continental crust, on the other hand, is formed from the accumulation of sediments and the melting of rocks.
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| What Is the Difference Between Oceanic Crust and Continental Crust? |
Density
The difference in density has an impact on isostacy of crust floating on the semi-fluid upper mantle (asthenosphere), with continental crust (about 2.7g/cm3) rising or floating above oceanic crust (about 3.5 g/cm3).
Age
The continental crust is older than the oceanic crust. This fact can be easily explained by the recycling process of the oceanic crust. The recycling process does not happen to the continental layer. Consequently, this ensures that the oceanic layer is always younger geologically.
Location
Because continental crust is less dense than oceanic crust it floats higher on the mantle, just like a piece of Styrofoam floats higher on water than a piece of wood does.
Thickness
Oceanic crust is much thinner than
continental crust.
Oceanic crust is typically about 5-10 kilometers
thick, while continental crust can be up to 40 kilometers thick.
Fossils
Oceanic crust is much younger than continental crust, so it does not contain as many fossils. Continental crust, on the other hand, is much older and contains a wealth of fossils. These fossils provide scientists with a valuable record of the evolution of life on Earth.
Mineralogy
Oceanic crust is rich in iron and magnesium, which are important for the formation of minerals such as magnetite and olivine. These minerals are important for the formation of rocks such as basalt and gabbro. Continental crust is rich in silicon and oxygen, which are important for the formation of minerals such as quartz and feldspar. These minerals are important for the formation of rocks such as granite and sandstone.
What Type of Crust is Found Under the Continents
The type of crust found under the continents is continental crust, also known as sial (rich in silicates (SiO₂ ) and aluminum (Al)) due to its composition of silicates and aluminum. This type of crust differs significantly from the oceanic crust that lies beneath the oceans. Continental crust is buoyant and floats on the denser mantle, allowing continents to rise above the ocean floor.