Feeling old? Check this out.

When I first saw the rock pile, through a couple hundred yards of sparse mountain hardwood, it looked as though the boulder had been stacked atop a section of bedrock. I wondered how it got there.

[pullquote]Mud that had become home to swamp plants was compressed into anthracite coal, to be mined several million years later by Irish laborers.[/pullquote]I knew it was not from glacial action. Between 2.5 million years and about 12,000 years ago, glaciers made multiple forays over North America. Some scientist believe that, left to its own devices, another Ice Age could occur, though we humans seem to be doing an excellent job of keeping the heat turned up.

The blanket only covered Pennsylvania nearly to Pittsburgh in the west, and almost to Allentown in the east. Here in central Pennsylvania, there was only frozen ground – tundra and permafrost, like in Alaska, but no glaciers.

My search for answers led me to a geology professor retired from his post at Dickinson College. Noel Potter, 75, has seen some rocks.

“There are knobs like this all up and down South Mountain,” he said, adding “They’re called ‘tors.’”

He explained that when temperatures were above freezing, water entered crevices and faults in the rocks. When temperatures fell, water – which expands in volume about 10 percent as it turns to ice – broke apart the smaller pieces from under the main boulder like a wedge would split a piece of oak firewood. Over time, the smaller rocks slid down hill from the high spot that was the larger boulder’s support.

At 12,000 years, the humungous boulder seems old, but in terms of the 4.6 billion-year-old planet, even it was young.

A company a few miles from that “tor” mines rock it crushes into the grit used on roofing shingles. The 600-million-year-old rock, called basalt, was created when an ocean called “Iapetus” opened in the vicinity of the current Appalachian Mountains, and a molten mineral soup gushed up through the crack and cooled suddenly in the water. The rapid cooling resulted in a mountains of tiny crystals ideally suited for crushing into the purpose they now serve.

Around 300 million years ago, the east coast of the United States slid across the space that would become the Atlantic Ocean, to become part of the west coast of Europe. It was the making of Pangaea, a giant continent formed when New York, New Jersey and eastern Pennsylvania crashed into Ireland and Spain and folded up the Allegheny Mountains.

Some geologists think the Alleghenies were once as high as the Andes Mountains of South America. A few hundred million years of wind, rain and ice can carve some serious graffiti into a mountain.

Mud that had become home to swamp plants was compressed into anthracite coal, to be mined several million years later by Irish laborers. Extinct plants and marine life became natural gas, to be stored in what would be called Marcellus Shale. (Most of that formation is under about two-thirds of Pennsylvania, but it takes its name from an outcropping in Marcellus, New York.)

Dinosaurs appeared 100 million years later, leaving footprints and bones in the mud in and near Gettysburg before they vanished from the planet.

Then, at about the aforementioned 2.5 million-year to 11,700-year mark, the ice overran portions of the earth and freezing spring water broke big rocks into little ones, leaving high hills and mountain peaks marked by piles of boulders, like monuments carved in place to battles fought by an ever-changing roster of combatants.

Some of those combatants have been human – our ancestors – but that is a story for another telling.

I would like to be around to wander the hills and see how long it takes that boulder to disappear. Another 12,000 years, or so, I reckon. I don’t think I can wait that long.

I may have to come back.