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After the Cretaceous, a new era of geologic time began; the Cenozoic era, which means the era of "recent life". Traditionally, the first period of the Cenozoic was called the Tertiary , [ 131 ] however recent recommendations of the International Commission on Stratigraphy discourage its use, with the correspondent time span divided between the ...
Later, the Yarmouth (Yarmouthian) stage in Illinois was defined on the basis of the Yarmouth Paleosol (Soil), developed in the surface of what were thought at that time to be "Kansan" glacial tills, and buried by Illionian glacial tills of the Glasford Formation in southeast Iowa and east-central Illinois. At this time, it was incorrectly ...
Because defining a GSSP depends on finding well-preserved geologic sections and identifying key events, this task becomes more difficult as one goes farther back in time. Before 630 million years ago, boundaries on the geologic timescale are defined simply by reference to fixed dates, known as "Global Standard Stratigraphic Ages" (GSSAs).
Each period is marked below the era bar on top of its subdivided epochs and stages. Each stage is assigned an age in mya , an acronym for million years ago, which is the age at which it began. Most of these ages are derived from astronomical cycles in sediments, magnetic data, biostratigraphic data, and radiometric dating methods.
Geologic Time – Period prior to humans. 4.6 billion to 3 million years ago. (See "prehistoric periods" for more detail into this.) Primatomorphid Era – Period prior to the existence of Primatomorpha; Simian Era – Period prior to the existence of Simiiformes; Hominoid Era – Period prior to the existence of Hominoidea
The North American land-mammal-age system was formalized in 1941 as a series of provincial land-mammal ages. [2] The system was the standard for correlations in the terrestrial Cenozoic record of North America and was the source for similar time scales dealing with other continents.
(Click to zoom) See legend below This is the legend for the North American geological map above. Geologic map of North America. The geology of North America is a subject of regional geology and covers the North American continent, the third-largest in the world. Geologic units and processes are investigated on a large scale to reach a ...
The Gasconadian Stage is the 1st stage of the Ordovician geologic period in North America and of the Lower Ordovician Canadian Epoch, coming immediately after the Late Cambrian Trempealeauan and preceding the middle Canadian Demingian Stage.