Geology & Fossils
Most of Kentucky’s rocks and fossils are very ancient, dating back more than 230 million years to the Paleozoic Era. Most Kentucky fossils are of marine invertebrates. In coal country, you may find both marine invertebrates and fossils of land plants.
Like many states, Kentucky also hosts the remains of creatures that lived during the Pleistocene Epoch, or Ice Age. These include mammoths, mastodons, ground sloths, bears, tapirs, and giant beavers.
Ice Age fossils from Kentucky played an important part in early paleontology. Mastodon fossils discovered along the Ohio River near Louisville in 1739 were the first fossils from the New World to be studied by French naturalists.
One of the most famous fossil sites in the United States is Big Bone Lick. Licks are places where animals come to obtain salt or other minerals. They are often called salt licks, or mineral licks, because visiting animals lick or gnaw the earth.
In the mid-18th century, when Kentucky was one of Virginia’s western territories, Big Bone Lick was discovered on the banks of Big Bone Lick Creek. At the lick were the bones of animals unlike any living animals. These included tusks and unusually large teeth. Native Americans said they came from an animal they called “big buffalo.” They believed it still survived beyond the Great Lakes.
Thomas Jefferson obtained many fossils from Big Bone Lick for his studies. He sent some bones to Europe. French naturalists recognized the tusks as belonging to elephants. But the teeth were not like elephant or mammoth teeth. They thought they were hippopotamus teeth.
Jefferson thought the tusks and teeth came from the same animal. He suspected the animal was an elephant. But no living elephant lives above the tropics. Was there an American elephant that was adapted to a colder climate?
From explorers, Jefferson received reports of great unknown beasts still roaming the wilderness. He asked Lewis and Clark to keep a lookout for the great Incognitum, as it was called. Lewis and Clark even visited Big Bone Lick to collect fossils.
Examining bones from Big Bone Lick, French naturalists finally described the American Incognitum as a new species — the American mastodon. Mastodons were ancient elephants. They generally lived farther south than mammoths. Mastodons browsed on leaves while mammoths ate grass.
Fossils in Our Lives
Kentucky’s most important mineral resources are fossils. These are coal, oil, and natural gas. Oil and gas were formed by marine animals. But coal was formed by plants that lived on land.
Coal is formed in lowland areas where plants grow near the sea, lakes, or in swamps. The formation of coal begins when plant remains are covered with water. Because oxygen is kept away from the dead plants, they do not completely decay, but leave behind carbon. This is the beginning of a coal seam.
When the water retreats, another forest may grow. If it is also covered by water, another coal seam begins to form.
But it is not coal yet. First, the plants become peat, which is about 50-60 percent carbon. As the seams are buried under other seams or sediments, the pressure changes the peat to lignite or brown coal. This is about 70 percent carbon. If you broke apart a piece of lignite, you could still see some plant material.
More pressure changes the lignite to bituminous coal, which is 75-85 percent carbon. The best coal — anthracite — may be almost 100 percent carbon. If you broke a piece of anthracite, you would see nothing resembling a plant.
Anthracite is the most valuable coal because it burns slowly with little flame and almost no smoke. Anthracite is also the hardest coal to mine because it is usually buried deepest.
Most coal in the Northern Hemisphere is from the Pennsylvanian Period, which began more than 330 million years ago. Amphibians ruled the land during the Pennsylvanian.
Most coal in the Southern Hemisphere, however, is from the Permian Period. The Permian Period followed the Pennsylvanian. During the Permian, the continents came together, forming a super-continent. Coal forests that once grew near the sea or rivers were stranded far from water. Much of the land became desert. The Permian Period marked the end of the Paleozoic Era. It was after the Permian that dinosaurs evolved. Some coal was formed during the Jurassic Period, when dinosaurs ruled the land.
Most of Kentucky’s coal comes from the Eastern Coalfield in the Appalachian Plateau. There are also large coal deposits in the Western Kentucky Coalfield. This coalfield is part of the Illinois Basin, which stretches into neighboring states. Much of Kentucky has been strip-mined. This causes erosion and flooding.
The map below illustrates the ages of Kentucky’s bedrock. Click a region to learn about the fossils of that region, or click the text links below the map to learn about a region’s geological history. The Tertiary period belongs to the Age of Mammals, the Cretaceous Period to the Age of Dinosaurs. All other periods represent the distant past before dinosaurs evolved. (Courtesy Kentucky Geological Survey) Or click the PaleoZoo Time Links above and to the right to get a broader view of these time periods.
Click the links below to learn about the geological history of Kentucky’s regions:
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