Sol definition, the syllable used for the fifth tone of a diatonic scale. See more.
Examples of index fossils. Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages).
Geogolists know the age of certain fossils, which are known as 'index fossils'. When they find these index fossils in certain rock layers, they know the age of the rock layers. sedimentary rock cant be dated with radioactivity because it is a mixture of many different rocks. but there are certain layers that can be radioactively dated. fossils are used for the layers in between.