One of the layers of the Earth found below the lithosphere is the asthenosphere. It is a layer composed mainly of solid rock that is subjected to so much pressure and heat that it can behave in a plastic way and flow. It is called a moldable layer because of its texture and composition. This layer has numerous practical applications in the knowledge of our planet and in the field of geology.
In this article we are going to tell you everything you need to know about the asthenosphere.
Key features
Rocks located in the asthenosphere have a lower density than those found in the Earth crustThis allows the tectonic plates of the lithosphere to move over the Earth's surface as if they were floating. They do this movement through the climbing rocks and they do it very slowly.
One way to describe the asthenosphere is the upper mantle. We remember that the Earth's layers are divided into three: crust, mantle, or core. The areas around the planet where we find the asthenosphere closest to the Earth's surface are beneath the oceans. This is where some areas with very little lithosphere thickness are found. Thanks to these areas, the composition and structure of the asthenosphere can be investigated in depth.
The overall thickness of this layer of the Earth ranges from 62 to 217 miles. Its temperature cannot be measured directly but can be known through indirect investigations. It is believed that it can range between 300 and 500 degrees Celsius. Due to this intense heat it becomes a completely ductile layer. That is, it has a texture that can be molded as if we were dealing with something similar to putty.
As we mentioned before, the rocks have a lower density and are partially molten. This is due to the mixing of the high temperatures together with the great pressure they are enduring.
Convection currents in the asthenosphere
Surely you have heard of the convection currents of the Earth's mantle. These convection currents will be thanks to the fact that heat from one place is transferred to another through the movement of a fluid such as molten rock. The heat transfer function of convection currents are those that drive the earth's ocean currents, atmospheric climate, and geology.
It's thanks to this movement of internal temperatures and molten rock that tectonic plates can shift. This is the main reason why continents aren't fixed in place, but shift each year, albeit by minimally recognizable distances. In just about 10.000 years the continents have moved only one kilometer. However, if we analyze this on a scale of geological time, we can affirm that, in the future within millions of years, it is possible that the tectonic plates will once again form what was once known as the supercontinent called Pangea.
Convection is different from conduction, since the latter involves the transfer of heat between substances that are in direct contact. What causes the convection currents of the mantle are molten rocks in the depths that circulate due to temperature changes. These rocks are in a semi-liquid state, so they can behave like any other fluid. They rise from the bottom of the mantle and then become warmer and less dense due to the heat of the Earth's core.
As the rock loses heat and enters the Earth's crust, it becomes relatively cooler and therefore denser. It then descends back toward the core. This constant circulation of molten rock is believed to directly contribute to the formation of volcanoes, earthquakes, and continental drift.
Speed of convection currents and importance of the asthenosphere
The speed at which mantle convection currents travel is typically about 20 mm/year, so it can hardly be considered a significant value. This convection is higher in the upper mantle than the convection near the core. Just one convection cycle in the asthenosphere can take around 50 million years. For this reason, we have mentioned before the importance of analyzing all these processes through geological time. The deepest convection cycle in the mantle can take approximately 200 million years.
Regarding the importance of the asthenosphere, we can say that it influences the atmosphere through the movements of the ocean and continental plates. At the same time, the position of the continents and ocean basins also changes the way air and climate move around the planet. If it weren't for these convection currents, the movement we've mentioned called continental drift wouldn't exist. It's responsible for the formation of mountains, volcanic eruptions, and earthquakes.
Although these events may be considered devastating in the short term, there are numerous benefits on a geological time scale such as the formation of new plant life, the creation of new natural habitats and the stimulation of the adaptation of living beings. The various impacts that the asthenosphere has on Earth serve to allow life to occur in greater diversity, and a vital aspect is that it is also directly related to the Tectonic plates.
Furthermore, the asthenosphere is also responsible for the creation of new Earth's crust. These zones are located at mid-ocean ridges, where convection causes the asthenosphere to rise toward the surface. As the partially molten material erupts, it cools and forms new crust.
I hope that with this information you can learn more about the asthenosphere.