Ohio rocks have some interesting stories to tell, and lucky for us, geologists can read those rock-bound tales like a book. In fact, the Buckeye States geologic history is full of surprises: rocks that once were alive, rocks that burn and rocks that whisper revealing clues about our prehistoric past.
Did you know that Ohio wasnt always a four-season kind of state? Before the age of the dinosaurs, warm, shallow seas covered this land. For 325 million years, the trilobite an early relative of todays lobsters and shrimp flourished within these tropical waters. Today, like the ancient salty sea in which they swam, the history of trilobites is literally written in rock, especially, in southwest Ohio.
Its been estimated that at least 20,000 different kinds of trilobites once crawled and swam along the sea floor, eating mud and chasing other aquatic creatures. Trilobites had hard outer shells, which they shed many times over a lifespan, creating numerous fossils for modern-day rock hounds to discover. Most trilobites were one-to-two-inches long and, when disturbed, theyd roll up like a pill bug to protect their bellies and legs.
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| Ohio's Official State Fossil |
Ohios official state fossil is a trilobite genus known as isotelus (pronounced eye-so-TEE-lus). It was the T-rex of its kind, a predator reaching as much as 28 inches in length.
Geologists calculate that trilobites disappeared from Ohio some 245 million years ago. Today, fossils imbedded in shale are all that's left of one of the most successful organisms that ever lived. If youre interested in fossil hunting, consider visiting Caesar Creek State Park in Warren County, which has a museum display to help you identify your find.
Across the state in Perry County, another geologic tale is told at New Straitsville, which can tout itself as one hot town! For the past 119 years, underground fires have burned through coal mines lying beneath the otherwise peaceful village. Sometimes flames and fumes escaped from the ground, making life unpleasant for residents. At other times, the fires smoldered, remaining hidden from view.
The fires were deliberately set in October 1884 during a contentious labor dispute. Disgruntled mine workers sent blazing railroad cars into mine openings; over several days, the unstoppable fire spread throughout the entire coal seam.
By the 1930s, the fires had reached dangerous levels. Flames, smoke, and poisonous gases routinely belched from fissures and old mine openings. Some homes were lost, cisterns boiled, yards collapsed, and, it was said, potatoes baked right in the garden.
In 1938, workers finally managed to slow down the fire and significantly contain it, but they could not put it out completely.
These days, while the hot earth has cooled somewhat, it's a pretty good bet the devil's still cooking down there. Experts have no plans, however, to open up the ground to see whats going on because that would just let air in, giving fuel to the flames and making things worse.
Since the fires were set more than a century ago, millions of tons of coal worth about $50 million have gone up in smoke. When will the fires burn out? Who knows, but experts estimate things will keep on smoldering down under for perhaps another 100 years.
An even odder geologic tale is told by the Serpent Mound in Adams County. If that coiled earthwork isnt mysterious enough, another nearby enigma has also stumped geologists. Serpent Mound lies on the western edge of a circular area about four miles in diameter. Beneath it, the bedrock has been disturbed, intensely cracked, jumbled, and dislocated. To geologists, it is obvious that some major disturbance occurred here, but exactly what happened has been cause for debate since the early 1800s.
The circle of fractured bedrock features three rings, one inside the other (like a bulls-eye), with the oldest rocks sticking up highest in the center. So what caused these eons-old rocks to rise up? On the one hand, it's typical of an impact crater caused by a meteorite (picture a small asteroid, weighing about two billion tons, smashing into the Earth at 15 miles per second)! Or it could also be a crater caused by an underground explosion, such as an eruption of explosive gases or ground water heated by molten rock deep inside the Earth.
Confusion intensified when early studies could find no evidence to support either theory no volcanic material or meteorite debris. Geologists weren't even sure when it happened some time between 345 million and 125,000 years ago a vast spread of geologic time.
But after all, a good geologic puzzle requires time to be solved. The Ohio Geological Survey is close to publishing a report on the rocky riddle. Through the examination of rock core samples, their study gives every indication that a meteorite hit the site some 260 million years ago. That was so long ago the Appalachian Mountains had not yet fully formed! Skeptics still exist, according to Ohios top geologist Tom Berg, but hes convinced the mystery has been unraveled.
Tales told by Ohios geology are amazing and diverse. From glaciers and mastodons to ancient river valleys and coastal swamps, it's all here to see, written in stone.