Earth vs Mother Earth

Earth

name
  • The personification of the Earth or earth, (chiefly) as a fertile woman or (religion) goddess. 

  • The third planet of the Solar System; the world upon which humans live. 

Mother Earth

name
  • The personification of the Earth, (chiefly) conceived as a fertile, nurturing, and loving mother. 

  • The goddess of the earth in various cultures. 

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