layer vs lower mantle

layer and lower mantle both are nouns.

Word	Noun	Adjective	Verb	Adverb
layer	Yes	No	Yes	No
lower mantle	Yes	No	No	No

As nouns, lower mantle is a hyponym of layer; that is, lower mantle is a word with a more specific, narrower meaning than layer:

layer: a relatively thin sheetlike expanse or region lying over or under another
lower mantle: the deeper part of the mantle

layer (noun)	lower mantle (noun)
thin structure composed of a single thickness of cells	the deeper part of the mantle
a hen that lays eggs
single thickness of usually some homogeneous substance
an abstract place usually conceived as having depth
a relatively thin sheetlike expanse or region lying over or under another

layer (verb)	lower mantle (verb)
make or form a layer