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Pennsylvanian

Geologic period
The Pennsylvanian is, on the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly 323.2 million years ago to 298.9 million years ago. Wikipedia
Chronological unit: Subperiod
Lower boundary definition: First appearance of the Conodont Declinognathodus nodiliferus
Lower boundary GSSP: Arrow Canyon, Nevada, United States; 36°44′00″N 114°46′40″W / 36.7333°N 114.7778°W
Lower GSSP ratified: 1996
Upper boundary GSSP: Aidaralash, Ural Mountains, Kazakhstan; 50°14′45″N 57°53′29″E / 50.2458°N 57.8914°E