Understanding the concept of time in seconds, minutes, days, years, and even centuries is easy for us to comprehend. However, the concept of geologic time is very hard for most of us to wrap our brain around. How can you put into perspective 4.6 billion years, the estimated age of the earth? Let’s try. It would take you 95 years to count to one billion if you averaged 3 seconds per number. (remember when you get to 999,999,999 it takes longer to say it). If you spent $100.00 per day, it would take you 27, 360 years to spend one billion dollars. Hopefully these examples put things into perspective.
Geologists have divided Earth’s history into a series of time intervals. These time intervals are not equal in length like the hours in a day or days in a week. This is because geologic time is divided using significant events in the history of the Earth. For example, the boundary between the Permian and Triassic is marked by a global extinction in which a large percentage of Earth’s plant and animal species were killed. Eons are the largest intervals of geologic time and are hundreds of millions of years in duration. Eons are divided into smaller time intervals known as eras. Very significant events in Earth’s history are used to determine the boundaries of the eras. Eras are subdivided into periods. The events that bound the periods are wide-spread in their extent but are not as significant as those which bound the eras. We all can relate to the Triassic and/or Jurassic period, this was the time of the dinosaurs. In the time scale you can see that the Paleozoic is subdivided into the Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician and Cambrian periods. This is the “period” when Nelson Ledges was being formed. Finer subdivisions of time of the periods are frequently subdivided into epochs. Subdivision of periods into epochs can be done only for the most recent portion of the geologic time scale. Many scientists believe that we have entered into a new epoch, The Anthropocene, this time period is characterized by human-influence. This is based on overwhelming global evidence that atmospheric, geologic, and hydrologic process, are now altered by humans. Especially with the advent of the atomic era.
Enough science talk, back to Nelson Ledges. At the time Nelson Ledges was formed, Ohio was located on the equator. This was during the Pennsylvanian epoch of the Carboniferous period. This was the age of insects, amphibians and ferns. This is when the first reptiles began roaming the earth’s surface. It is also known as the age of coal. At this time, Ohio was under an ancient sea. This was 120 million years BEFORE the dinosaurs! That is why you don’t find any fossil evidence in the rocks in or around Nelson Ledges. During this time, there was significant movements of land. The Land mass know as Laurasia was merging with the land mass called Gondwana to create one huge land mass called Pangea. Pangea subsequently broke apart into the seven continents we know today. This collision cause the formation of the Appalachian Mountains, the Acadian Mountains, and the Caledonia Mountains in northern eastern Canada. Remember that Ohio was sitting on the equator during this time. It was hot, humid, and very wet. As a result, the mountains in north eastern Canada began eroding. Huge quantities of quartz (lucky stones) began traveling down from the north along with huge quantities of sand. Over the next 10 million years the Ledges were formed. So the next time you pick up a lucky stone from Nelson Ledges, you might give it the respect it is due, since it is 300 million years old!