Asthenosphere

noun

/æsˈθɛnəsfɪər/

The semi-molten, ductile layer of Earth's upper mantle lying beneath the lithosphere, approximately 100–300 km deep, on which the rigid tectonic plates float and move — its partial melting and convection currents provide the driving force for plate tectonics.

✍️ Usage 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

upper mantle layerductile mantle zoneplastic mantlelow-velocity zonesphere of weaknessrheosphere

Antonyms

lithospherecrust

🌱 Word Family

asthenosphere (n), asthenospheric (adj); No standard verb or further derivatives in English

🔡 Root

Greek asthenes (weak, without strength) + sphaira (sphere); coined by geologist Joseph Barrell, 1914.

📜 Etymology

From Greek asthenes (ἀσθενής, "weak, without strength") + sphaira (σφαῖρα, "sphere"); coined by geologist Joseph Barrell in 1914 to describe 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.

🌍 Geography 📖 Seen in: Plate Tectonics & Volcanism — Continen...

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