| 词条 | Pennsylvanian Subperiod |
| 释义 | Pennsylvanian Subperiod geochronology second major interval of the Carboniferous Period, lasting from 318.1 to 299 million years ago. The Pennsylvanian is recognized as a time of significant advance and retreat by shallow seas. Many nonmarine areas near the Equator became coal swamps during the Pennsylvanian. These areas are mined for coal today. See Carboniferous Period. |
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