boulder vs earth

boulder

verb
  • To engage in bouldering. 

noun
  • A particle greater than 256 mm in diameter, following the Wentworth scale 

  • A large marble, in children's games. 

  • A session of bouldering; involvement in bouldering. 

  • A large mass of stone detached from the surrounding land. 

earth

verb
  • To bury. 

  • To hide, or cause to hide, in the earth; to chase into a burrow or den. 

  • To burrow. 

  • To connect electrically to the earth. 

noun
  • The people on the globe. 

  • The lair or den (as a hole in the ground) of an animal such as a fox. 

  • A region of the planet; a land or country. 

  • Any planet similar to the Earth (our earth): an exoplanet viewed as another earth, or a potential one. 

  • A connection electrically to the earth ((US) ground); on equipment: a terminal connected in that manner. 

  • The ground, land (as opposed to the sky or sea). 

  • Soil. 

  • The world of our current life (as opposed to heaven or an afterlife). 

  • The aforementioned soil- or rock-based material, considered one of the four or five classical elements. 

  • Worldly things, as against spiritual ones. 

  • Any general rock-based material. 

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