Geological periods

The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period Ma (million years ago) to the beginning of the Cretaceous Period, 143.1 Ma. The Jurassic constitutes the second and middle period of the Mesozoic Era as well as the eighth period of the Phanerozoic Eon and is named after the Jura Mountains, where limestone strata from the period were first identified.

The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 Ma (million years ago). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geological period of the entire Phanerozoic. The name is derived from the Latin , 'chalk', which is abundant in deposits from the latter half of the period. It is usually abbreviated K, for its German translation .

The Triassic (; sometimes symbolized as 🝈) is a geologic period and a stratigraphic system that spans 50.5 million years from the end of the Permian Period 251.902 Ma (million years ago) to the beginning of the Jurassic Period 201.4 Ma. The Triassic Period is the first and shortest geologic period of the Mesozoic Era, and the seventh period of the Phanerozoic Eon. The start and the end of the Triassic Period featured major extinction events.

The Cambrian ( ) is the first geological period of the Paleozoic Era and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 486.85 Ma.

The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.7 million years from the end of the preceding Silurian period at million years ago (Ma), to the beginning of the succeeding Carboniferous period at Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied.

The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years, from the end of the Carboniferous Period Ma (million years ago) to the beginning of the Triassic Period 251.902 Ma. It is the sixth and last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.

The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at Ma (million years ago) to the beginning of the Devonian Period, Ma. The Silurian is the third and shortest period of the Paleozoic Era, and the third of twelve periods of the Phanerozoic Eon. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera we

The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the Permian Period, Ma. It is the fifth period of the Phanerozoic eon. In North America, the Carboniferous is often treated as two separate geological periods, the earlier Mississippian and the later Pennsylvanian.

The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 43.75 million years from the end of the Cambrian Period Ma (million years ago) to the start of the Silurian Period Ma.

The Quaternary ( , ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the Phanerozoic eon. It follows the Neogene Period and spans from 2.6 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.6 million years ago to 12 thousand years ago) and the Holocene (12 thousand years ago to today); a proposed third epoch, the Anthropocene, was rejected in 2024 by International Union of Ge

The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the first period of the Cenozoic Era, the tenth period of the Phanerozoic and is divided into the Paleocene, Eocene, and Oligocene epochs. The earlier term Tertiary Period was used to define the time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remain

The Neogene ( ) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period Ma (million years ago) to the beginning of the present Quaternary Period Ma. It is the second period of the Cenozoic and the eleventh period of the Phanerozoic. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868). The earlier term T

The Ediacaran ( ) is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

The Cryogenian (from , meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.

The Tonian (from , meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic Era and followed by the Cryogenian.

The Stenian Period ( , from , meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically due to the scarcity of Precambrian fossils and lack of reliable zonation. It is preceded by the Ectasian Period and followed by the Neoproterozoic era and the Tonian period.

The Siderian () is the first geologic period in the Paleoproterozoic Era and Proterozoic Eon. It lasted from  to  million years ago (Ma), spanning 200 million years, and is followed by the Rhyacian Period. Instead of being based on stratigraphy, these dates are defined chronometrically.

The Rhyacian () is the second geologic period in the Paleoproterozoic Era. It spans 250 million years and lasted from to million years ago (Ma), following the Siderian Period and preceding the Orosirian Period. These dates are defined chronometrically rather than stratigraphically.

The Statherian (; , meaning "stable, firm") is the fourth and final geologic period in the Paleoproterozoic Era, lasting from to million years ago (Ma) and spanning 200 million years. It follows the Orosirian Period and precedes the Calymmian Period, with the latter belonging to the Mesoproterozoic Era. Instead of being based on stratigraphy, these dates are defined chronometrically.

The Ectasian Period (from , meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The Calymmian (from , meaning 'cover') is the first geologic period in the Mesoproterozoic Era, lasting from to million years ago (Ma) and spanning 200 million years. It follows the Statherian Period from the Paleoproterozoic Era, and precedes the Ectasian Period. Instead of being based on stratigraphy, these dates are defined chronometrically.

The Orosirian (; , meaning "mountain range") is the third geologic period in the Paleoproterozoic Era. It spans 250 million years and lasted from to million years ago (Ma), following the Rhyacian Period and preceding the Statherian Period. Instead of being based on stratigraphy, these dates are defined chronometrically.

idealized composite unit of the geologic record representing the totality of rock strata laid down during a certain period of the geologic time scale

Earth history between 1.8 and 0.8 billion years ago, characterized by tectonic stability, climatic stasis, and a slow biological evolution with very low oxygen levels and no evidence of glaciation