Era, a very long span of geologic time; in formal usage, the second longest portions of geological time (eons are the longest). (2020, August 27). In general usage, an eon (sometimes spelled aeon) is a period of time arbitrarily designated by humans. These efforts made it easier for geologists to make more precise divisions of e… This period is the first new one added in 120 years. Geologic time, the extensive interval of time occupied by the geologic history of Earth. The colors were specified by the Committee for the Geologic Map of the World in 2009. This last point in time is the start of a division of geological time called the Phanerozoic Eon. An era is composed of one or more geological periods. Human activity has transformed the planet; some scientists have proposed a new epoch, the "anthropocene," to describe this new period of life on Earth. Most of them were aquatic; the most famous examples are trilobites, small arthropods (creatures with exoskeletons) whose distinct fossils are still being discovered today. ThoughtCo, Aug. 27, 2020, thoughtco.com/geologic-time-scale-eons-eras-periods-1440796. How to use era in a sentence. Period, in geology, the basic unit of the geologic time scale; during these spans of time specific systems of rocks were formed. Geologists have divided the history of the Earth into a series of time intervals. These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history. The stratigraphic, or rock, term that corresponds to “era” is “erathem.”. The rocks under a specific area have a significant impact on how that land can best be used. Eons are divided into eras, which are further divided into periods, epochs, and ages. There are 22 defined periods. The Geologic Time Scale is the history of the Earth broken down into four spans of time marked by various events, such as the emergence of certain species, their evolution, and their extinction, that help distinguish one era from another. 1. a major division of geological time; an era is usually divided into two or more periods Familiarity information: GEOLOGICAL ERA used as a noun is very rare. Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. These are fossil bacteria, and for most of Earth history, life was simple. This is the branch of earth sciences that deals with the concept of geological time and dating the sequence of events throughout the Earth’s history. See more. This eon is named after Hades, the Greek god of the underworld, and during this period the Earth was extremely hot. the Victorian era see thesaurus at period COLLOCATIONS ADJECTIVES/NOUN + era a new era The talks signalled a new era of cooperation between the two countries. era ... (geology) a length of time that is a division of an aeon; Word Origin mid 17th cent. Although water was present at this time, the heat would have boiled it away into steam. The Proterozoic was also the period in which the Earth's first glaciers formed. Synonym Discussion of era. The Proterozoic eon began about 2.5 billion years ago and ended about 500 million years ago when the first complex lifeforms appeared. The reason for this is that the geological time is divided by important events in World history. Our editors will review what you’ve submitted and determine whether to revise the article. It was the last period of the Precambrian's Neoproterozoic Era. Two or more Eras form an Eon, the largest division of geologic time. More complex animals appeared in the oceans about 565 million years ago, and became much more common about 542 million years ago. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Corrections? Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages. Multicelled organisms first appeared during this time. of duration—eons, eras, periods, epochs, and ages. Instead, the length of time intervals is variable. Eras. SEE PREVIOUS WORDS. For example, although the date listed for the beginning of the Ordovician period is 485 million years ago, it is actually 485.4 with an uncertainty (plus or minus) of 1.9 million years. (c) 2013 Andrew Alden, licensed to About.com, Inc. (fair use policy). 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