The Archean Eon began when the Earth’s crust cooled enough that our continental plates began to form and liquid water covered most of the planet. The earliest signs of life began to form as simple single-celled organisms called prokaryotes. These prokaryotes survived in the shallow waters for hundreds of millions of years until a new microbe came around to work towards making the Earth much different. Cyanobacteria developed oxygenic photosynthesis, taking light and water and turning it into energy with a simple byproduct called oxygen (this is very important… obviously). It took hundreds of millions of years before this did much, but then the Great Oxygenation Event happened. This event killed off almost all the anaerobic life but then life adapted. It discovered the great potential oxygen gives for creating energy. Severson Dells would be underwater for most of this time. 

The Proterozoic Eon started with the beginning of an oxygenated atmosphere. This timespan also developed the first oxygen-dependent animals called Ediacara fauna. The Earth during this time also went through a number of glaciations that took place during this eon. The crust also developed and broke into many supercontinents starting with the supercontinent of Columbia between 2.1 billion and 1.8 billion years ago and then Rodinia which was about 1.0 billion years ago. This eon ended with the Cambrian explosion. During both of these supercontinents Severson Dells nature center would probably be on a landmass called Laurentia and it might have been rotated about 90° clockwise from its current position.

Now we reach the Eon that includes the modern day! The Phanerozoic Eon began 538 million years ago when plants and animals proliferated across all of Earth's surface. This expansion of animal and plant life is called the Cambrian explosion and was the beginning of complex life forming quickly on the Earth. This is the eon where we are all much more familiar with many things that happen like the dinosaurs, ice age, and the modern era. Even now with how close we are getting to the modern era, Severson is unrecognizable from its modern day form but now we get to view some influential parts that built our land into what it is today.

At this time Severson Dells started to sink slowly down allowing a shallow, tropical ocean from the South that covered  the land. Little bits of sand and marine organisms (such as shells, algae, and coral) would sink to the bottom of the ocean and slowly over many years compact together with the weight of everything over them and transform into sedimentary rock. This rock became different types of sandstone and limestone. It was around this time the Dells at Severson Dells began to form as well (but they weren’t the Dells yet because they were just part of the ocean floor slowly being formed)!

Around this time was the formation of the third major supercontinent called Pangea. As the land masses came together, the ocean retreated from the future land of Severson Dells, and large river systems flowed across all of Illinois. At this point Severson was actually much closer to the equator than it is now so much more consistently warm weather. Hills and valleys formed all around Severson for hundreds of millions of years and DINOSAURS ROAMED the land. Unfortunately all evidence of dinosaurs in Illinois was erased for reasons that will be explained later. The odds of large scaled beasts roaming the Illinois landscape are very high, though, given they all lived on one major landmass that had many parts connecting them together. Around 200 million years ago Pangea started to break apart and slowly move towards the continental places that are likely much more familiar to us on a world map. The Dinosaurs lasted longer than Pangea but after about 200 million years being around they went extinct. Practically a blink of an eye when compared to the  age of the Earth (3.68% of Earth's life so far had dinosaurs existing).

The Ice Age was directly responsible for shaping the land that Severson Dells has been developed on. During this time large swaths of land were covered by glaciers including Severson Dells. The first glacial period was called pre-Illinoian and it carved over Severson taking away the hills and valleys and flattening it. Then the next glacial period called the Illinoian took away more land, carving away at the millions of years of rock that formed before it. This left the landscape very flat (which is why Illinois is the second flattest state in the United States). From this land, massive prairies covered much of Illinois. The millions of years worth of rock dragged away included many fossils (like all the dinosaur fossils) that were likely in the rocks. Over 400 million years worth of rock was torn out from Illinois exposing the rocks that formed when it was a warm sea. So the fossils that you can find at the dells include crinoids, corals, and Brachiopods (which are all water creatures that live in oceans). Once the glaciers left and water began to flow, it carved out our little nook of the woods and the dells were formed showing the beauty of time passing.

Now we come to the Holocene, this was when the ice age began to fade and the Earth became warmer. This is the current time period we live in and it only covers the last 10,000 years. So much has happened in 10,000 years, this is the era where humans have truly taken over and expanded worldwide. Every bit of our written history is included in this Epoch. The civilizations that have risen and fallen, the wonders we have built, the wars we have waged. All in just a fraction of a fraction of the Earth’s total life. Even though Severson Dells Nature Center has existed for less than 50 years- an incomprehensibly small portion of Earth’s time- we are thankful to have you as a part of our story. Each moment we share together betters this beautiful Earth and ensures that humans will continue to enjoy it for millennia ahead.