Devonian delight

The Devonian Period fell in the middle of the Paleozoic era, between about 420 million and 360 million years ago, when the amount of oxygen in Earth’s atmosphere was 75 percent of what it is today, and high CO2 levels kept temperatures warm and sea levels high. Nevertheless, primitive plants began to invest in real estate on land and build primordial forests, and diverse species of fish developed to compete with other marine life, including trilobites, brachiopods and coral. The earliest four-limbed vertebrate animals, tetrapods, crawled out of the crowded seas and began to take up residence alongside marshes and estuaries, a surprise evolutionary move that led to global gentrification. Future descendants would include creatures as distinct as the gastornis (a giant and sadly long extinct flightless bird), garter snakes, the naked mole-rat and yours truly. (We humans would first show up in our ancestors’ scrapbooks on the second-to-the-last page.)

To faraway and hypothetical aliens this blue orb hanging around the sun would have looked like a very different marble then. Euramerica was still debating whether or not to hook up with her bigger planetmate Gondwanaland, and Pangaea remained a mere twinkle in the Carboniferous period’s eye. Places we now call the Midwest and Mississippi River valley were covered by shallow seas that, sometime later in the period, began to dabble with acidification that helped lead to the Late Devonian extinction. Then nothing of real interest happened until the middle of the 19th century, when workers at the quarry of a brick and tile business outside of Rockford, Iowa, discovered “seashells” discrete from the red clay that was the company’s bread and butter. A century and a half after that, conservationists working to preserve prairie habitat in the Hawkeye State turned the defunct quarry into a county preserve, and the Floyd County Fossil & Prairie Center came into being.

I rolled in after a gray drive from the west at 10:30 in the morning, but a sign on the museum door said it was closed until 1 p.m., and the breeze was a bit chilly. I dug out my winter coat from the trunk and put on some gloves and a knit cap and headed off toward a field with a pathway mowed out of the tall green grass. I thought I’d have the place to myself, at least, to wander around the acreage and take some pictures, but as I neared the trailhead, I began to hear children squealing and shouting back and forth in excitement. A minute later I came upon a weathered sign that said, “Start Collecting!” and at that moment everything changed. I glanced down and immediately spotted a seashell-shaped stone about the size of a dime beside my right foot and picked it up. Sure enough, it was the fossil of a 365-million-year-old brachiopod.

This was a bit of a surprise. I hadn’t known the quarry grounds were open to collectors. The truth is I hadn’t researched the site at all. I pocketed my prize and walked a bit further, climbed to the top of a ridge and found dozens of people scrambling over piles of rocks and gravel and scouring the open quarry as if on the hunt for gold. A couple days of rain had eroded and shifted the soil, so new finds were likely, and folks had parked in a different lot down the road and come from the opposite direction, turning the drizzly morning into a family outing. I steered away from the dads and kids on the vertical cliffs and the women hanging back near the water down below and stuck to gulleys and eroded ravines closer to the top. For the next hour and a half I dug my cold fingers into the mud and filled my coat pocket with fossilized evidence of that Devonian inland sea: nothing uncommon, nothing spectacular, but a few dozen pieces of ancient history to keep for myself.

What drove me to collect these fossils, squinting through the wrong glasses, muddying my shoes, the fingers of my right hand numb? I don’t have a need for any more rocks, and the ones I found on Saturday morning certainly aren’t of any value. Marine shells from the distant past are the most common fossils in the world. And yet I can’t help picking up rocks when I like them — I still have quite a few I found as a child. Maybe it’s a compulsion brought on by instinct: The inherent fragility of life on this planet is found within rocks, and fossils in particular tell fascinating stories. But that’s just intellectual posturing. At my age I should know better than to overthink what I enjoy. It’s a terrible habit that ruins all the fun.