Ever since the film Jurassic World was released last year, young visitors to Crossroads seem intent on searching for dinosaur bones. And while we have fossils which are hundreds of millions of years older than the beasts that roamed the Earth during the Jurassic period, Crossroads at Big Creek is just not a good place to hunt for evidence of dinosaurs.
Back some 425 million years (or so) ago, the area we now call the Door Peninsula was covered by a warm, shallow sea. Conditions were ideal for fossil formation. Creatures including corals, cephalopods, and crinoids secreted hard shells. Many of these shells were preserved in the dolomite which forms our bedrock.
This bedrock is sedimentary, a type of rock which forms in layers. Obviously, if one layer of rock is formed and then another and another are formed on top of it, the bottom layer is the oldest, usually. [There are exceptions, but not in our region.] If there are many layers of rock, the bottom layers are oldest, the top layers are the youngest. Each layer is younger than the one below it.
This makes perfect sense and the concept is very important to geologists. [You can tell how important a concept is by the length of the name.] Geologists call it The Law of Superposition.
So it follows that if we find fossil corals at Crossroads, and they are more than 300 million years older than dinosaurs, then dinosaur fossils should be closer to the surface. IF there were dinosaurs here. And we don’t know if they were in Door County. It’s rather a mystery just what Wisconsin was like because there is a major… MAJOR….. gap in the fossil record. Millions of years worth of fossil evidence is missing. Scientists call it The Lost Interval.
A few years ago, I wanted to illustrated this situation to a Learning if Retirement class. I had an old text book–outdated to the point that it was downright inaccurate. I took that worthless book, and in front of the group, ripped almost half of the book right out of its binding, leaving only the first half and then two or three pages at the very end of the book intact. As I desecrated the book, a collective gasp went up from the class. Noting their visceral reaction [apparently destroying even a worthless book is an unpardonable sin] I vowed never again to tear up a book in public. But this is exactly what geologic forces did in our region.
Where did the evidence go? Not sure. It is hard to imagine that in all of that time, layers of rock did not form. Presumably, many layers of rocks formed and then were eroded away by weather. Probably, additional of layers were scoured away by Ice Age glaciers. Based on rocks found in unglaciated areas of North America, scientists speculate there were younger rocks and that during the Age of Dinosaurs and the Age of Mammals, animals live in Door County. But those chapters of geologic history are gone. Nobody will ever know what was here or when.
So when kids come fossil hunting at Crossroads–as participants in our family programs or just as an outing– they will find fossils of creatures that are ancient beyond imagining or else bones of creatures which lived during the last ten thousand years.
Our Summer Family Programs are offered at 10:00 Monday through Thursday in the Collins Learning Center. The programs are free and open to the public. We welcome participants of all ages—families not required.