The Geologic Time Scale is divided into four eons, ten eras, 22 periods, and several epochs and ages. Each eon, era, period, and epoch is defined by major geological or paleontological events. The eons are the Hadean, Archean, Proterozoic, and Phanerozoic. The Phanerozoic Eon is the eon o...
Of course, these geologic units are not equal in length. Eons, eras, and periods are usually separated by a significant geologic event and are unique in their climate, landscape, and biodiversity. The Cenozoic era, for example, is known as the "Age of Mammals." The Carboniferous period, on...
The period is the basic unit of geological time in which a single type of rock system is formed. Two or more periods comprise a geological Era. Two or more Eras form an Eon, the largest division of geologic time. Some periods are divided into epochs. ...
Learn what the geologic time scale is. Identify eons, eras, periods, and epochs on the time scale, and study the history and development of the geologic time scale. Related to this Question How was the geologic time scale developed?
The eras of the Proterozoic and Phanerozoic eons are each further divided into periods,shown in this geologic time scale. The periods of the three Phanerozoic eras are divided in turn into epochs. (See the Phanerozoic epochslisted together.) Epochs are subdivided into ages. Because there are so...
Geological history is not counted in specific years but in ranges of time divided into eras, periods, and epochs. Geologists use a variety of methods to identify the age of rocks, including measuring the decay of radioactive isotopes, to determine when certain geological even...