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).
The age of fossils can sometimes be determined by radiometric dating, which is based on the constant rate of decay of radioactive isotopes. The time required for half of a radioactive isotope to decay is called the half-life of that isotope. For example, the isotope carbon-14 has a half-life of 5,730 years.