示し準じゅん化か石せき

noun

index fossil; guide fossil

Technical term in geology and paleontology for a fossil used to define and identify geological periods.

• 示し準じゅん化か石せきは地ち層そうの年ねん代だいを決きめるのに役やく立だつ。

  Index fossils are useful for determining the age of strata.