BharatNotes Asthenosphere
nounUsage in a UPSC answer
Just as the rigid lithosphere of statute can move only because it rests upon the yielding asthenosphere of administrative discretion, so a constitutional order endures not through rigidity alone but through the pliant lower stratum of conventions and institutional flexibility that absorbs the persistent stresses of a changing polity.
Synonyms
Antonyms
Word Family
asthenosphere (n), asthenospheric (adj); No standard verb or further derivatives in English
Root
Greek asthenes (weak, without strength) + sphaira (sphere); the name is credited to J. Barrell (1914).
Etymology
From Greek asthenes (ἀσθενής, "weak, without strength") + sphaira (σφαῖρα, "sphere"); the name, credited to J. Barrell (1914), describes the weak, deformable zone beneath the strong lithosphere.
Memory Hook
A-STHENO = 'a' (without) + 'sthenos' (strength); think of the comic-book strongman who LOSES his strength: the asthenosphere is the Earth's WEAK, soft layer beneath the strong, rigid lithosphere.
How This Word Works in UPSC Writing
The weak, semi-solid (not molten) layer of the upper mantle beneath the lithosphere, over which the plates move. Its mechanical behaviour is what matters: because it deforms plastically it permits both plate motion and isostatic adjustment. Note that the lithosphere-asthenosphere division is defined by mechanical strength, not by chemical composition, which is exactly the distinction that separates it from the crust-mantle boundary.
Don’t Confuse It With
The asthenosphere is the weak, ductile upper mantle layer. The lithosphere is the rigid outer shell of crust plus uppermost mantle, defined mechanically. The crust is defined chemically and is separated from the mantle by the Moho. The mesosphere or lower mantle lies beneath the asthenosphere and is more rigid again.
Hindi Meaning
दुर्बलतामंडल (durbaltāmandal); स्थलमंडल (sthalmandal) is the lithosphere.
Common Questions
- What is the asthenosphere?
- The weak, semi-solid (not molten) layer of the upper mantle beneath the lithosphere, over which tectonic plates move.
- How is the lithosphere-asthenosphere boundary different from the crust-mantle boundary?
- The lithosphere-asthenosphere boundary is defined by mechanical strength. The crust-mantle boundary, marked by the Moho, is defined by chemical composition.
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