What are the Eras of Geologic Time?
The geologic time scale has been determined bit-by-bit over the years through relative dating, correlation, examination of fossils, and radiometric dating. Eon = Largest division of time scale. The Eons, in order from oldest to youngest, are Archean, Proterozoic, and Phanerozoic. The Archean and the Proterozoic are sometimes grouped into the a unit called the Precambrian. The Precambrian consists of approximately 87% of geologic time. This is the time before abundant life with hard parts such as shells. The term Phanerozoic means “visible life”, and it refers to the time when many animals had hard parts such as shells and bones, which are readily preserved as fossils. Era = A major division of geologic time, divisible into geologic periods. The Phanerozoic Eon is divided into three eras. In order from oldest to youngest, the eras are as follows: • Paleozoic Era- “ancient life” (such as trilobites) • Mesozoic Era – “middle life” (such as dinosaurs) • Cenozoic Era – “recent life” (such a
