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A period is equivalent to a chronostratigraphic system. [14] [13] There are 22 defined periods, with the current being the Quaternary period. [2] As an exception two subperiods are used for the Carboniferous Period. [14] An epoch is the second smallest geochronologic unit.
13 wrz 2024 · The geologic time scale is the “calendar” for events in Earth history. It subdivides all time into named units of abstract time called—in descending order of duration— eons, eras, periods, epochs, and ages.
28 lut 2020 · During this period, the Great Oxygenation Event transformed the Earth's atmosphere, allowing for the evolution of aerobic organisms. The Proterozoic was also the period in which the Earth's first glaciers formed. Some scientists even believe that during the Neoproterozoic era, about 650 million years ago, the surface of the Earth became frozen.
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.
Periods of geological time are subdivided into epochs. In turn, epochs are divided into even narrower units of time called ages. For the sake of simplicity, only the epochs of the Paleogene, Neogene, and Quaternary periods are shown on the time scale at the top of this page.
24 maj 2024 · The Geologic Time Scale is the history of the Earth broken down into four spans of time: the Precambrian, Paleozoic, Mesozoic, and Cenozoic Eras. These eras of the Earth are marked by various events, such as the emergence of certain species, their evolution, and their extinction, that help distinguish one era from another.
Figure 12.1 shows you what the geologic time scale looks like. We now live in the Phanerozoic eon, the Cenozoic era, and the Quarternary period. Sometimes, periods are further divided into epochs, but they are usually just named “early” or “late”, for example, “late Jurassic”, or “early Cretaceous”.
