Info Nuggets: The tectonic tandem

• It is solid, brittle and divided into tectonic plates.
• Thickness: Roughly 100 km, but varies (thinner under oceans, thicker under continents).

• It is semi-solid (viscoelastic), capable of plastic flow.
• Acts as the lubricating layer over which tectonic plates move.

• Lithosphere = Crust Rigid upper mantle
• Asthenosphere = Part of the upper mantle (ductile zone)

• Lithosphere is broken into tectonic plates that float on the asthenosphere.
• Movement causes earthquakes, volcanism and mountain formation.

• Earthquakes and tsunamis are closely tied to lithospheric plate interactions.
• Asthenosphere’s plasticity influences the rate and pattern of plate movement.

• Heat from the asthenosphere is a key source of geothermal energy.

• Tectonic activity influences mineral distribution and oil-gas basins.

• Helps in studying continental drift, sea-floor spreading, and mantle convection.

1. Increased seismic activity (e.g., Turkey-Syria earthquake, Nepal tremors, Himalayan instability).
2. Advances in satellite geodesy and seismic tomography revealing new insights into mantle and lithosphere behaviour.
3. Deep-sea drilling projects and geothermal exploration have renewed focus on asthenosphere studies.
4. Concerns over plate subduction zones and their role in megaquakes.
5. Debates over continental drift theory and tectonic modelling in light of climate change and isostatic rebound.

UPSC practice questions

1. Define lithosphere and asthenosphere. Explain how they differ in physical properties.
2. What role does the asthenosphere play in plate tectonics?
3. Why is the lithosphere significant in the context of earthquakes?

1. Compare and contrast the lithosphere and asthenosphere with reference to their structure, behaviour and geophysical relevance.
2. Discuss the importance of understanding lithosphere-asthenosphere interactions in the context of disaster preparedness and sustainable development.

1. “The dynamics of the lithosphere and asthenosphere are central to Earth’s geophysical and environmental evolution.” Discuss with examples.
2. Examine the role of the asthenosphere in enabling plate tectonics. How do recent geoscientific findings alter our understanding of Earth’s interior?