A geologic era is a subdivision of geologic time that is a separate classification that divides the PhanerozoicEon into three parts timeframes. The the Paleozoic, the Mesozoic, and the Cenozoic represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries, the P-T boundary between the Paleozoic and the Mesozoic and the K-T boundary between the Mesozoic and the Cenozoic. There is evidence that catastrophic meteorite impacts played a role in demarcating the differences between the eras. The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ... In general usage, an eon (also spelled aeon) is a very short period of time. ... The Paleozoic is a major division of the geologic timescale, one of four geologic eras. ... The Mesozoic is one of three geologic eras of Phanerozoic eon. ... The Cenozoic Era (sometimes still Caenozoic in the United Kingdom) is the most recent of the four Categories: Cenozoic ... Ever since recorded history began, and probably before, people have found pieces of rock and other hard material with indentations from the remains of dead organisms. ... In biology and ecology, extinction is the ceasing of existence of a species or group of taxons. ... The Permian-Triassic extinction event, labeled End P here, is the most significant extinction event in this plot for marine fossiliferous genera. ... The Cretaceous-Tertiary (KT) extinction event, also known as the KT boundary (from German: Kreide-Tertiär-Grenzschicht), was a period of massive extinction of species, about 65. ... Artists impression of a major impact event. ...
The Hadean, Archean and Proterozoic form what is informally called the Precambrian Era. This covers the four billion years of Earth history prior to the appearance of hard-shelled animals. The name Hadean refers to a geologic period: the time before 3800 million years ago (mya). ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... In geology, the Proterozoic is an eon prior to the first abundant complex life on earth. ... The Precambrian or Cryptozoic is the period of the geologic timescale from the formation of Earth (around 4500 million years before the present [BP]) to the evolution of abundant macroscopic hard-shelled fossils, which marked the beginning of the Cambrian, some 542 million years BP. Remarkably little is known about...
During the hiatus between the late Precambrian and Paleozoiceras most of the evidence of the earth's early history was destroyed by erosion.
In North America, the era began with submerged geosynclines, or downward thrusts of the earth's crust, along the eastern, southeastern, and western sides of the continent, while the interior was dry land.
During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the geosynclines from the interior.
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