Let us know if you have suggestions to improve this article (requires login). era - A division of geologic time of several hundred million years in duration. The definition of an era is a period of time in history that is unified by cultural or historical factors. Quiz Review. The Proterozoic eon began about 2.5 billion years ago and ended about 500 million years ago when the first complex lifeforms appeared. a date or an event forming the beginning of any distinctive period: The year 1492 marks an era in world history. These time intervals are not equal to the length of the hour in a day. Early humans, including Homo habilis, first appeared about 2.8 million years ago, and modern humans (Homo sapiens) first appeared about 300,000 years ago. In general usage, an eon (sometimes spelled aeon) is a period of time arbitrarily designated by humans. of duration—eons, eras, periods, epochs, and ages. He works as a research guide for the U.S. Geological Survey. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. 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. Conformable: Definition. 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. The Cenozoic, Mesozoic, and Paleozoic are the Eras of the Phanerozoic Eon. Oceans as we know them today did not appear until the Earth's crust began to cool many years later. View More Submit. Andrew Alden is a geologist based in Oakland, California. This period is the first new one added in 120 years. 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. The Structure of Geologic Time The Geologic Eras of Time Eons > Eras > Periods > Epochs. Geologists have divided the history of the Earth into a series of time intervals. How to use era in a sentence. Of course, these geologic units are not equal in length. An era is smaller than an eon and longer than a period. Data from Geologic Time Scale of 2015. geologic time, geological time the time of the physical formation and development of the earth (especially prior to human history) Geologic time spans are divided into units and subunits, the largest of which are eons. Geologic Time. However, some believe the first landmass on Earth was a supercontinent known as Ur. The most recent geologic eon is the Phanerozoic, which began about 540 million years ago. The oldest fossils are between 3 billion and 3.5 billion years old. Some scientists even believe that during the Neoproterozoic era, about 650 million years ago, the surface of the Earth became frozen. During the Mesozoic era, which began about 250 million years ago, dinosaurs ruled the planet. Definition. The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time.It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. With the help of clocks, calendars, and appointment books, we organize our lives around time. Formal geologic time begins at the start of the Archean Eon (4.0 billion to 2.5 billion years ago) and continues to the present day. Others believe it was a supercontinent known as Vaalbara. These creatures were the largest to ever walk the Earth. Geology is the study of the physical features and history of Earth . There are 22 defined periods. It includes the study of organisms that have inhabited our planet. The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time.It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. A period of time characterized by particular circumstances, events, or personages: the Colonial era of US history; the Reagan era. During the Cambrian period—the earliest part of the Phanerozoic—the first complex organisms appeared. The stratigraphic, or rock, term that corresponds to “era” is “erathem.”. During this period, the cooling of the Earth's crust allowed for the formation of the first oceans and continents. Intervals of geological time are given formal names and grouped into a hierarchy according to their length: Eon, Era, Period, Epoch, Age and Chron, in decreasing time intervals. 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