Paleontology and geology
The Precambrian: There are no Precambrian rocks in Mississippi. The state, as such, did not exist during this time.
The Paleozoic: The youngest rocks found in Mississippi are marine in origin, formed during the Late Devonian. A sea with pockets of deep, oxygen-poor water covered the northeastern part of the state at this time. The fossils in these dark-colored rocks are primarily plant fragments and the remains of animals that could swim above the oxygen-starved depths. The sea continued to cover portions of the state into the later part of the Paleozoic and provided a home to molluscs, crinoids, brachiopods, and trilobites. During the Late Carboniferous, the water retreated as vast amounts of sediments were poured into the sea from the erosion of newly formed mountains. Forests of primitive trees and fern-like plants grew on the resulting broad coastal plains. By the end of the Paleozoic, the entire state was above sea level and exposed to erosion.
The Mesozoic: Mississippi remained above sea level for much of the Mesozoic. During the later part of this era, however, a shallow sea flooded the region as North and South America moved farther apart during the breakup of the supercontinent of Pangea. The rocks originally deposited as sediment on the floor of this sea contain abundant fossils of both invertebrates and vertebrates. Pieces of petrified wood are also common.
The Cenozoic: Warm, tropical seas periodically flooded southern Mississippi during the early part of the Cenozoic, while the northern part of the state remained above sea level. Marine fossils include whales, sharks, and bony fish, as well as numerous molluscs and other invertebrates. Fossilized wood found in northern Mississippi provides evidence of the forests and swamps that existed there at this time. In the Late Cenozoic, most of the state was covered by coastal plain and shallow sea. Glaciers far to the north of the state affected the climate and caused fluctuations in sea level. Blankets of wind-blown silt (loess) eroded from the Mississippi River floodplain cover large areas in the northwestern part of the state. Fossil shells of various terrestrial and freshwater molluscs, as well as the fossil bones of a number of terrestrial mammals, have been recovered from the loess deposits.