What is the Asthenosphere?
The asthenosphere is a layer of the upper mantle of Earth located below the lithosphere. Despite the great difficulty in accessing the various layers of the Earth, the geographical sciences have allowed us insight into the different layers which make up the Earth. The three main parts are the Earth's crust, the mantle and the core, all in descending order towards the center of the Earth. Each of these parts has various sections and layers with their own distinct geological characteristics. While there is much we do not know about these hard-to-explore parts of the Earth, there are certain characteristics that are generally agreed upon by science.
At thedailyECO, we learn what we do know by asking what is the asthenosphere? We provide a definition of the asthenosphere with its characteristics and diagrams to better understand how are Earth was formed.
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What is the asthenosphere?
The asthenosphere is one of the layers of the Earth's upper mantle and is located directly below the lithosphere. The lithosphere is considered the superficial part of our planet which includes the Earth's crust and the lithospheric mantle. Since the lithosphere includes everything on top of the Earth's crust (including mountains and other high peaks), it ranges in depth depending on whether it is continental or oceanic.
The asthenosphere is directly below the lithospheric mantle and is formed by partially molten solid rocks that are subject to strong pressures and high temperatures. For this reason, the asthenosphere behaves as a plastic and ductile layer that can have some ability to flow. It is necessary to clarify that the asthenosphere is not a liquid layer, but rather the conditions of pressure and heat are responsible for the rock being in a semi-molten or ductile state.
You can learn more about how these parts of the Earth's mantle and crust affect geology with our article on what causes a volcano to erupt?
Characteristics of the asthenosphere
While we have provided a basic definition of the asthenosphere, we need to know its characteristics to better understand its form and function. We have already referenced two of the most important factors in the asthenosphere, specifically temperature and pressure. There are other essential characteristics which make the asthenosphere so important. They include:
- Chemical composition: in terms of the characteristics of the rocks (lithology) of the asthenosphere, its composition is made of a minimum 44% silica in the form of silicates.
- Density: the rocks that make up the asthenosphere have a lower density than the rocks of the Earth's crust.
- Temperature: although it is currently impossible to measure the temperature of the asthenosphere directly, indirect investigations have concluded that the temperature of the asthenosphere ranges between 300 to 500 degrees Celsius (572 to 932 ºF).
A the characteristics of the asthenosphere we have mentioned result in a fluid and malleable layer that allows continental drift. This is the displacement of continental masses and the movement of tectonic plates. These displacements and movements occur due to convection currents that occur when heat is transferred from one place to another through the movement of a fluid. In this case. it is through the movement of the semi-molten rock that makes up the asthenosphere.
With these characteristics of the asthenosphere in mind, we can take a closer look at its climactic and geological processes. There include the following:
- Movements of the tectonic plates: from the convection currents of the asthenosphere, the movements of the tectonic plates occur. These movements are responsible for the emergence of mountain formations and volcanoes. In addition, the movement of tectonic plates causes other geological phenomena such as tremors and earthquakes. Learn about how an earthquake occurs with our related article.
- Oceanic ridges: similarly, convection currents cause the asthenosphere to rise towards the surface, creating new crust. When this occurs in the ocean, this helps with the formation of oceanic ridges. Learn more about how a mid-oceanic ridge is formed with our related article.
- Atmosphere: the asthenosphere is also influenced by the activity that happens in the asthenosphere. This is mainly due to the movements of the oceans and the position of the continental masses, phenomena that modify the circulation of the air and, as a result, the climate.
You can discover more about the atmosphere and how it affects the Earth with our articles on what is the mesosphere and what is the troposphere?
When was the asthenosphere discovered?
The concept of asthenosphere has evolved as the research methods and theory have progressed. In this way, we can say that:
- In 1899 the concept of asthenosphere arose for the first time when Clarence Dutton, a renowned geologist. He differentiated the Earth's mantle into a rigid zone, which is inferred to be the lithosphere, and below this, a weak zone, which we could deduce to be the asthenosphere.
- In 1914 , the term asthenosphere specifically emerged to explain the phenomenon of isostasy, defined as the state of gravitational equilibrium of the plates of the lithosphere.
Since then, there have been many controversies about the nature of the asthenosphere. This is due to the difficulty of exploring this layer for study. As a result of such controversy, the concept of the asthenosphere has changed profoundly in recent decades.
Despite this controversy, it is widely believed that the asthenosphere plays an important part in plate tectonics. This movement of the Earth's lithosphere has a direct impact on both oceanic and continental structures. It results in our world looking as it does.
While it is difficult enough to understand the layers of the planet Earth, the understanding of different types of celestial bodies is even more difficult. You can learn what we do know with our article on what are the different layers of the sun.
If you want to read similar articles to What is the Asthenosphere?, we recommend you visit our Facts about Earth and the universe category.
- Rodríguez, CF, Chaves, FMA, & Virella, FA (2013). Asthenosphere: to be or not to be . Teaching of Earth Sciences: Magazine of the Spanish Association for the Teaching of Earth Sciences.
