Geologic Time Scale

• The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time
• Geologic Time Scale is a timeline illustrating Earth's history based on geologic events and life forms
• The geologic time scale has four major divisions: Eon, Era, Period, and Epoch
• We are currently in the Holocene Epoch of the Quaternary period of the Cenozoic Era
• The Precambrian Eon refers to the earliest part of Earth's history and covers approximately 88% of Earth's history
• The Phanerozoic Eon is the current geologic eon in the geologic time scale
• The Paleozoic Era is the earliest of the three geologic eras of the Phanerozoic Eon
• The Paleozoic Era began with the breakup of one supercontinent and the formation of another
• The Cambrian period, known for ushering in an explosion of life on Earth, occurred 53 million years ago. This Cambrian explosion included the evolution of arthropods
• The Ordovician period was a time of intense diversification of marine animal life known as the Ordovician radiation
• The Silurian period was a time of considerable environmental changes, including the melting of large glacial formations
• The Devonian period, known as the 'Age of Fishes,' had diverse and abundant fish populations
• The Carboniferous period is named for its coal-bearing nature and was coined by geologists William Conybeare and William Phillips
• The Permian period was a time of beginnings and endings, marking the appearance of mammal-like reptiles
• The Mesozoic Era, known as the 'Middle Life' era, saw the rapid diversification of life and the dominance of giant reptiles and dinosaurs
• The Mesozoic Era is subdivided into the Triassic, Jurassic, and Cretaceous periods
• The Cenozoic Era began about 65 million years ago and continues today, characterized by the evolution of mammals and flowering plants
• The table of geologic periods presented here agree with nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy.
• Eon

  The largest time span of the geologic time
• Paleozoic Era


  is the longest of the Phanerozoic eras
• Paleozoic Era


  Plants became widespread
• Triassic Period

  is the first and shortest period of the Mesozoic Era
• The Jurassic is named after the Jura Mountains in the European Alps, where limestone strata from the period were first identified.
• Cretaceous Period

  extinction of the dinosaurs (except birds).
• Cenozoic Era 


  This era is sometimes called the “Age of Mammals. Climate was warm and mild