The Silurian Period of the Paleozoic Era occurred between 408 and 433 million years ago. The Silurian world was very different from the world of today. North America was shaped much differently and was located so that the equator passed through it. Much of North America was covered by a warm, shallow sea, called the Silurian Sea. This sea held coral reefs and marine wildlife. Some fossils can still be found today.
Limestone was deposited in the sea, layer upon layer, which geologists estimate began to form 450 million years ago, and is known as the Mississippian layer. The second layer is called the Jefferson and the third layer is the Gasconade Dolomite. It was primarily in this third layer that Missouri caves were formed.
Before the first big upheaval 42 to 46 million years ago, this shallow sea consisted of 60 feet of water over about 200 feet of silt. Caves began to form after this upheaval occurred. In all, six ice ages have occurred over North America at widely spaced intervals of geologic time.