fossil vs period piece

fossil

noun
  • Any preserved evidence of ancient life, including shells, imprints, burrows, coprolites, and organically-produced chemicals. 

  • The mineralized remains of an animal or plant. 

  • An extremely old or outdated person. 

  • Anything extremely old, extinct, or outdated. 

  • A fossil word. 

period piece

noun
  • A work which evokes the era in which it was produced, but may not have any other especial features. 

  • A work of art or drama which evokes a particular historical era. 

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