Read the article and learn all the characteristics, physical and chemical properties, functions, importance and parts of the largest inner layer of our planet.
What is the Earth’s mantle?
The earth mantle It is the solid layer of the earth that lies between the earth’s crust and the core, it represents about 83% of the total volume of the planet and reaches a depth of 2900km below the surface.
Its importance lies in the fact that the mantle is where the so-called convective processes occur that allow all the external dynamics of the planet and the movement of the tectonic plates to be generated.
Theoretically the mantle It is divided into two main layers: the upper and lower mantle, however it is currently known that there is a “transition” zone between both layers that is due to possible partial fusion processes.
Characteristics and properties of the earth’s mantle
Below, we present a summary of the main characteristics and properties of the Earth’s mantle in a table, and later we discuss each characteristic in more depth.
| Characteristics/Properties | earth mantle |
|---|---|
| thickness or thickness | 2900km |
| Density | From 3.3 gr/cm3 to 5.5gr/cm3 |
| Temperature | 1200°C to 3300°C |
| Pressure | Up to 1.8 million atmospheres |
| Thickness | 3485 km approximately |
| Volume | 87% of the total volume of the earth |
| Dough | 63% of the total mass of the earth |
| Layers, parts or subdivision | Upper mantle, transition zone and lower mantle. |
| Depth | Up to 2900 km |
| upper contact | With the earth’s crust at 7 to 70 km (Mohorovicic discontinuity) |
| bottom contact | With the outer core at 2900 km |
| Temperature | From 1400°C (upper mantle) to 3000°C (lower mantle) |
| associated rocks | peridotites |
| Associated minerals | Olivine, pyroxenes, garnets, chromite. |
| Chemical composition | Ultramafic (less than 45% Silica-SiO2) and rich in iron and magnesium |
| Condition | Solid |
Differences between the upper and lower mantle
| Upper mantle | Lower mantle | |
|---|---|---|
| Temperature | 1200°C to 2000°C | 3300°C |
| Condition | plastic and solid | Solid |
| composition | iron, oxygen, silicon, magnesium and aluminum | iron, oxygen, silicon, magnesium and aluminum |
| Thickness | 600km | 2885km |
Density
The earth mantle It is characterized by having a density range that varies from 3.3 gr/cm3 to 5.5 gr/cm3, from the top to the base.
It is clear that at a greater depth the mantle rocks are subjected to great pressure, which causes the mineral grains to be very compact, which causes the density to increase, especially in the lower mantle.
In addition, the iron and magnesium enriched composition of the mantle causes the density to increase as well.
Volume and mass
The mantle It represents about 83% of the total volume of the planet and 63% of its total mass, this makes it the most voluminous and thickest layer on earth.
Depth
The The earth’s mantle begins when the earth’s crust ends and depending on that we can say that it can start 7km below the surface in contact with the oceanic crust and 70km below the surface in contact with the thicker continental crust.
The deepest part of the mantle would be in contact with the outer core at a depth of 2900 km.
Temperature and pressure
The temperature in the mantle is such that it varies from 1200°C to 3300°C, it is clear that the lowest temperature will be in the upper part (upper mantle) and the highest temperature will be in contact with the outer core in the lower mantle. While the pressure can reach up to 1.8 million atmospheres at the base of the lower mantle.
Associated rocks
The mantle of the earth It is composed mainly of ultramafic rocks, specifically peridotites.
This group includes Dunites, Harzburgites, Iherzolites, Wherlites, and Kimberlites.
Mineral composition
Because the earth mantle It is associated with ultrabasic rocks, it is normal for it to be rich in minerals such as olivine, pyroxenes (orthopyroxene, clinopyroxene), garnets, chromite, and even diamonds.
Chemical composition
The chemical composition of earth mantle It is also related to ultramafic rocks, that is to say, it generally has less than 45% silica (SiO2).
Regarding the percentage of magnesium oxide (MgO) it reaches 32%, while iron oxide (FeO) reaches at least 9%, in addition, it is rich in calcium oxide (CaO) up to 8.5%.
Mantle structure
The mantle is almost 2,900 kilometers thick and makes up about 80 percent of the Earth’s volume. Much of our knowledge of the mantle’s composition and structure comes from seismic data.
Seismic waves accelerate abruptly at the crustal-mantle boundary.
Seismic waves decrease again when they enter the asthenosphere at a depth of between 75 and 125 kilometers. The plasticity and partially molten character of the asthenosphere slow down seismic waves.
At the base of the asthenosphere, 350 kilometers below the surface, seismic waves speed up again because the increasing pressure overwhelms the effect of temperature, and the mantle becomes stronger and less plastic.
At a depth of about 660 km, seismic wave velocities increase again because the pressure is so great that minerals in the mantle recrystallize to form denser minerals.
The area where the change occurs is called the 660 km discontinuity.
The base of the mantle is located at a depth of 2,900 kilometers. Recent research has indicated that the base of the mantle, at the core-mantle boundary, may be so hot that, despite tremendous pressure, the rock in this region is liquid.
Parts or subdivision of the mantle
The researchers have concluded that the chemical composition of the mantle is approximately uniform throughout. However, the mantle can be subdivided into three distinct layers, delineated by seismic velocity discontinuities.
Although the mantle is normally divided into two main layers: the upper and lower mantle, it is currently known that there is a transition zone between the upper and lower mantle.
Upper mantle
- Temperature : 1200°C – 2000°C
- Condition : plastic / solid
- Composition : iron, oxygen, silicon, magnesium and aluminum
This is the layer between the Moho (Mohorovicic discontinuity) and a depth of about 400 km.
Below the ocean basins, the interval between about 100 km and 200 km has abnormally low seismic velocities.
This interval is known as the low speed zone. The slowness of seismic waves in the low velocity zone may be due to the presence of partial melting. In this case, 2–4% of the rock is produced as magma and it is the process that generates igneous rocks.
Note that the low velocity zone is only a part of the upper mantle and probably does not exist below the continents.
Furthermore, its chemical composition is similar to that of peridotite (less than 45% SiO2).
It behaves like a solid rock mass.
However, at the upper limit of this layer, lithospheric plates are formed, which are responsible for plate tectonics and the formation of plate limits (convergent, transform and divergent limits) in an environment of plastic mechanical behavior.
Mantle transition zone
This is the interval between a depth of 400 km and 670 km. Within this interval, we observe several abrupt jumps in the seismic velocity, probably due to a succession of phase changes in the mantle minerals.
Lower mantle
- Temperature : 3300°C
- Condition : solid
- Composition : iron, oxygen, silicon, magnesium and aluminum
This is the interval between a depth of 670 km and a depth of 2,900 km. Here, temperature, pressure, and seismic velocities gradually increase with depth.
It behaves like a solid rock mass.
Its chemical composition is ultra-basic (less than 45% SiO2) and enriched in iron and magnesium (18% MgO and 9% FeO).
What is the importance of the earth’s mantle?
The importance of the earth’s mantle lies in the fact that it is there where what is known as convection processes occurs, that is, where the heat of the earth causes convective zones to be generated that will allow the tectonic plates to move.
That is to say that the tectonic plates or lithospheric plates move on the asthenosphere due to the convection processes that occur in the mantle.
If you want to learn more about the lithosphere we recommend you click here
If you also want to know about the atmosphere click here