One of the Earth's layers located beneath the lithosphere is the asthenosphere . This layer, composed primarily of solid rock, is subjected to such intense pressure and heat that it can behave plastically and flow. It is called a malleable layer due to its texture and composition. This layer has numerous practical applications in understanding 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
The rocks in the asthenosphere are less dense than those in the Earth's crust . This allows the tectonic plates of the lithosphere to move across the Earth's surface as if they were floating. This movement occurs very slowly, as the rocks rise above the surface.
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 determined through indirect research. It is believed to range from 300 to 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 it were made of 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
You've probably heard of the convection currents in the Earth's mantle. These convection currents occur because heat is transferred from one place to another through the movement of a fluid, such as molten rock. The heat transfer function of convection currents drives Earth's ocean currents, atmospheric climate, and geology.
Thanks to this movement of internal temperatures and molten rock, tectonic plates can shift. This is the main reason why continents are not fixed in one place, but rather move each year, albeit by minimally perceptible distances. In just 10.000 years, the continents have moved only one kilometer. However, if we analyze this on a geological timescale , we can say that, millions of years from now, tectonic plates may once again form what was known as the supercontinent Pangaea.
Convection differs from conduction, which involves the transfer of heat between substances in direct contact. Convection currents in the mantle are caused by molten rock circulating deep within the Earth due to temperature changes. This rock is in a semi-liquid state, so it behaves like a fluid. It rises from the lower mantle after becoming hotter and less dense due to the heat from 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 of mantle convection currents is typically around 20 mm/year, so it can hardly be considered a significant value. This convection is higher in the upper mantle than near the core. A single convection cycle in the asthenosphere can take around 50 million years. This is why we previously mentioned the importance of analyzing all these processes over geological time. The deepest convection cycle in the mantle can last 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, they offer numerous benefits on a geological timescale, such as the formation of new plant life, the creation of new natural habitats, and the stimulation of adaptation in living organisms. The various impacts of the asthenosphere on Earth allow life to flourish in greater diversity, and a vital aspect is its direct relationship with plate tectonics.
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.