Hadean vs unlit

Hadean

name

  • The Hadean eon; part of the Precambrian supereon, spanning from around 4.6 to 4 billion years ago. 

adj

  • Pertaining to Hades or hell. 

  • Of, or relating to the geological eon. 

unlit

adj

  • Not lit 

How often have the words Hadean and unlit occurred in a corpus of books? (source: Google Ngram Viewer )