lifespan vs perpetuity

lifespan

noun
  • The length of time for which something exists or is current or valid. 

  • The length of time for which an organism lives. 

  • Some clams have lifespans far longer than those of human beings. 

perpetuity

noun
  • The quality or state of being perpetual; endless duration; uninterrupted existence. 

  • An annuity in which the periodic payments begin on a fixed date and continue indefinitely. 

  • Something that is perpetual. 

  • A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law. 

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