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The Mississippian is about twice as long as the Pennsylvanian , but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America , the two subperiods were long thought to have been more or less equal in duration .
 Mississippian, Pennsylvanian, Europe, North America
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Mississippian, Pennsylvanian, Europe, North America