Asthenosphere

Definition

The asthenosphere is a semi-fluid layer of the Earth's mantle located just below the lithosphere, approximately 100 to 200 kilometers beneath the Earth's surface. This layer plays a crucial role in plate tectonic movements as it provides a lubricating effect that allows the rigid plates of the lithosphere to glide over it. The asthenosphere is characterized by its ability to flow slowly, which is essential for processes such as seafloor spreading and the movement of tectonic plates.

5 Must Know Facts For Your Next Test

1. The asthenosphere extends from about 100 km to 700 km beneath the Earth's surface and is composed mainly of partially molten rock.
2. Its semi-fluid nature allows tectonic plates to move, causing geological activities such as earthquakes and volcanic eruptions.
3. The temperature in the asthenosphere ranges from about 1,300°C to 3,000°C, affecting its viscosity and flow properties.
4. Convection currents within the asthenosphere are driven by heat from the Earth's interior, contributing to plate movements and seafloor spreading.
5. The asthenosphere interacts with both oceanic and continental crust, influencing geological features like mid-ocean ridges and mountain ranges.

Review Questions

• How does the asthenosphere contribute to the movement of tectonic plates?
  • The asthenosphere contributes to the movement of tectonic plates by providing a semi-fluid layer that allows these rigid plates to glide over it. This layer's ability to flow slowly reduces friction between the lithospheric plates, facilitating their movement due to forces like convection currents generated by heat from the Earth's interior. Without this lubricating effect, plate tectonics would be significantly hindered.
• Discuss the relationship between the asthenosphere and seafloor spreading.
  • The asthenosphere plays a vital role in seafloor spreading by allowing tectonic plates at mid-ocean ridges to move apart. As magma from the mantle rises through cracks in the lithosphere at these ridges, it cools and forms new oceanic crust. The presence of the asthenosphere enables this magma to flow easily, leading to the continuous formation and expansion of ocean floors as tectonic plates separate.
• Evaluate how changes in temperature and pressure within the asthenosphere can affect geological activity on Earth's surface.
  • Changes in temperature and pressure within the asthenosphere can significantly impact geological activity on Earth's surface. Increased temperatures can reduce viscosity, enhancing flow rates and potentially leading to more vigorous convection currents. This can result in increased volcanic activity or shifts in tectonic plate movements. Conversely, changes in pressure may lead to solidification or alterations in material properties, which can affect how easily plates slide past one another and influence seismic events like earthquakes. Therefore, understanding these dynamics is crucial for predicting geological phenomena.

Related terms

Lithosphere:

The rigid outer layer of the Earth, consisting of the crust and uppermost mantle, which is divided into tectonic plates.

Mantle: The thick layer of Earth located between the crust and the outer core, composed of solid rock that behaves as a viscous fluid over geological timescales.

Plate Tectonics:

The scientific theory explaining the movement of the Earth's lithosphere through the interaction of tectonic plates on the asthenosphere.