asthenosphere

From Ancient Greek ἀσθενής (asthenḗs, “weak”) + -sphere.

• (UK) IPA^(key): /asˈθɛnə(ʊ)sfɪə/

asthenosphere (plural asthenospheres)

1. (geology) The zone of the Earth's upper mantle, below the lithosphere.
   • 2003, Bill Bryson, A Short History of Nearly Everything, BCA, page 192:

     To say that the lithosphere floats on top of the asthenosphere suggests a degree of easy buoyancy that isn't quite right.

   • 2004, Richard Fortey, The Earth, Folio Society, published 2011, page 79:

     The asthenosphere that underlies the surface plates is not liquid in any vernacular sense, although it is relatively plastic.