The Precambrian Eon, that vast expanse of earth's history prior to 550 million years ago, is not represented in the surface rocks in Kentucky. Rocks of Precambrian age occur in Kentucky, but are below the surface. We know very little about the Precambrian in Kentucky, largely because the rocks are so difficult to reach. Based on the few wells that have been drilled down to it and based on what we know about the Precambrian rocks elsewhere, we can make some inferences about the Precambrian in Kentucky.

The later part of the Precambrian Eon saw the collision of crustal blocks in what is now Kentucky. This collision created a chain of mountains, which were later eroded during the later part of the Precambrian and Cambrian. We are not certain whether Precambrian sediments are still recognizable at depth, because separating Precambrian from Cambrian rocks when they occur below the surface is difficult. Life during most of the Precambrian was restricted to bacteria and algae. Blue-green bacterial structures called stromatolites are found in Precambrian sedimentary rocks throughout the world. During the latest stages of the Precambrian, a variety of fossils of multicelled animals (metazoans), called the Ediacaran fauna, are also found all over the world. This fauna includes animals that have been interpreted as sea pens and jellyfish (Cnidaria), flatworms, grazing animals of unknown type, and other uncertain types. Perhaps stromatolites and the Ediacaran fauna occur in the deeply buried rocks of Kentucky, as well.