Originally published in Castine Patriot, May 23, 2013
Digging into the past of Maine’s geology
Naturalist Sarah O’Malley gives a crash course in plate tectonics
Sarah O’Malley describes how Maine—geologically speaking—became Maine at a talk at Witherle Memorial Library on April 29.
by Anne Berleant
Starting from one road in Sedgwick, Sarah O’Malley traced the geological beginnings of Maine. Now known for its rocky coast, it took millions of years of geological activity for the Maine we know today to evolve.
O’Malley, an adjunct professor of communications and ocean studies at Maine Maritime Academy, outlined her investigations in a talk at Witherle Memorial Library on April 29.
“I started thinking about my environment, my neighborhood,” she said, while searching for a Capstone Project, a requirement of the Maine Master Naturalist Program, a nonprofit organization started in 2011 to train volunteer naturalists.
O’Malley began her Capstone Project, a piece of research resulting in a tangible product, by exploring Walter Green Road in Sedgwick, “an old, disused road,” where she walked her dogs.
A 1960 photograph of the road showed an old house that contained a wreath making business. The house is now gone.
Starting with the question, “Who made this road?” O’Malley peeled back the geological layers 650 million years to when Maine was formed.
Using the relatively new theory of plate tectonics, O’Malley outlined how, starting billions of years ago, the earth’s continents broke apart and came back together, changing the earth’s surface until the continents as we know them today were formed. Tectonic plates are able to move because the Earth’s lithosphere, or crust, has a higher strength and lower density than the underlying upper mantle of the earth.
“Plates move about as fast as your fingernails grow,” O’Malley said.
She used the metaphor of a snowball—as more snow is packed around its base, forming layers, so did the movement of the earth’s tectonic plates pack layers onto the continents.
By three hundred million years ago, all the pieces of Maine were in the middle of the supercontinent Pangaea, which eventually broke apart into the continents we have today.
“Europe and North America came together and ripped apart, came together and ripped apart,” O’Malley said. As smaller “microcontinents” were “squished together in the middle,” sediment turned into rock.
Flash forward to the present, and O’Malley begins searching for bedrock, “really solid rock connected to the rest of the earth,” on Walter Green Road.
She showed a slide of one huge piece of rock sloping out of the ground—a familiar site in Maine—the only example she found on that road.
Working against tectonic action is erosion, “breaking down rocks chemically and physically, moving everything towards equilibrium.”
The second geological force came hundreds of thousands rather than millions of years ago, when glaciers began to melt.
The large boulders that mark Maine’s coastline appeared as the Ice Age ended. As glaciers receded, they left gravel and boulders, like “Elephant Rock” on Wadsworth Cove, O’Malley said.
That helped Maine’s rocky coast evolve.
When the ice melted, the sea rose. Over thousands of years, the frozen crust of the earth “bounced up” as it warmed and sea levels dropped.
“Then, the crust bounced down and stabilized a few thousand years ago,” said O’Malley.
Maine’s soil took “only 10,000 to 12,000 years to form…the glacial till of rocks and soil,” said O’Malley. “It takes a long time for soil to build up and we haven’t had a lot of time.”
The third force in geology, after tectonics and glaciers, is humans, “which is “still in progress,” said O’Malley.