If Ordovician continental blocks had similar hypsometries to modern continental blocks, glacially-induced regressions would have increased shallow water areas. Thus species/area effects cannot be invoked to explain extinctions during these regressions. Because late Ordovician sea level was so high, glacially-induced regressions of similar magnitudes to Quaternary regressions would have dramatically increased the input of dissolved load into the shallow sea. This ‘pollution’ effect may have been one cause of the extinctions.

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