This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. There is evidence that the P-T boundary was caused by the eruption of the Siberian Traps, and the K-Pg boundary was caused by the meteorite impact that created the Chicxulub crater. These eras are separated by catastrophic extinction boundaries: the P-T boundary between the Paleozoic and the Mesozoic, and the K-Pg boundary between the Mesozoic and the Cenozoic. The Phanerozoic Eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middle life" and "recent life") that represent the major stages in the macroscopic fossil record. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not thus "early Miocene" but "Early Jurassic."
EON TIMER REFRESH INTERVAL SERIES
For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in geochronology. Geologists qualify these units as "early", "mid", and "late" when referring to time, and "lower", "middle", and "upper" when referring to the corresponding rocks. Millions of Years (1st, 2nd, 3rd, and 4th)Ĭorresponding to eons, eras, periods, epochs and ages, the terms " eonothem", " erathem", " system", " series", " stage" are used to refer to the layers of rock that belong to these stretches of geologic time in Earth's history. Subdivision of an age, not used by the ICS timescale Units in geochronology and stratigraphy Segments of rock ( strata) in chronostratigraphyġ0 defined, several hundred million yearsĢ2 defined, tens to ~one hundred million years A polarity chron or just "chron" can be used as a subdivision of an age, though this is not included in the ICS system.Ĭarboniferous (Mississippian/Pennsylvanian)įormation of Earth to 4,000 million years ago Eons are divided into eras, which are in turn divided into periods, epochs and ages. This is because of the significance of the Cambrian Explosion, a massive diversification of multi-cellular life forms that took place in the Cambrian period at the start of the Phanerozoic. every eon but the Phanerozoic) can be referred to collectively as the Precambrian supereon. Finally, the Phanerozoic eon encompasses 541 million years of diverse abundance of multicellular life starting with the appearance of hard animal shells in the fossil record and continuing to the present. After about 2.5 billion years, oxygen generated by photosynthesizing single-celled organisms began to appear in the atmosphere marking the beginning of the Proterozoic. The first eon was the Hadean, starting with the formation of the Earth and lasting about 540 million years until the Archean eon, which is when the Earth had cooled enough for continents and the earliest known life to emerge. The largest catalogued divisions of time are intervals called eons. 3.4 Naming of geologic periods, eras and epochs.3.2 Establishment of primary principles.3 History and nomenclature of the time scale.The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS). The time scale was developed through the study and observation of layers of rock and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The geologic time scale ( GTS) is a system of chronological dating that classifies geological strata ( stratigraphy) in time. The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale. Other subdivisions reflect the evolution of life the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The Hadean eon represents the time before the fossil record of life on Earth its upper boundary is now regarded as 4.0 Ga ( billion years ago). This clock representation shows some of the major units of geological time and definitive events of Earth history.
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