The Everglades a huge freshwater marshland and in part peatland developed in recent geologic time during a globally controlled convergence of both climate change and sea level rise within a shallow bedrock trough located in Southern Florida. The recession of glaciers in northern North America at the end of the Pleistocene period and the change to a subtropical climate in Southern Florida provided both the abundant precipitation and the seasonal rainfall climate necessary for the generation of the Everglades wetland ecosystem. The rising sea level has undoubtedly retarded runoff and downward leakage out of the trough or helped to retain water within the Everglades basin. This, in turn, has allowed thick accumulation of peat (3 3.7 meters thick) to develop within the deeper parts of the basin.
Formation of the Everglades peatland, which is supported by a freshwater wetland system of seasonal flooding and dominated by marshes with scattered free islands, began on a large scale by about 5,000 years before present (YBP). Portions of the present Everglades area had become short flooded, seasonal, calcitic mud marshes around 6500 YBP or even earlier. Extensive areas of marsh peat, with basal dates in the 5000 4500 YBP range, indicate the widespread development or rapid expansion of wetland environment with long peat-forming hydroperiods early in the history of the Everglades.
A closer look at the Everglades' geology can be seen at the Eastern Coastal Ridge.
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