Wednesday, December 4, 2013
Strolling a beach, have you ever stopped and thought about just where all that sand has come from? A handful of sand can contain 10,000 stories. Some of them half a billion years old. Here’s the story of one grain.
It starts 600 million years ago, back when North America looked very different.
Maine didn’t even exist yet! Nor the rest of the eastern seaboard.
Somewhere near modern Ottawa, a storm brewed. It burst against an aged, weathered stump of a mountain. Rainwater lashed the dead granite,* seeping into tiny fissures.
A freezing night followed, cracking free a massive block of stone. Mid-morning’s thaw brought the block down, exploding into a thousand fragments. All tumbled into an ancient river, which tore them apart, setting a grain of sand free. For years that grain bounced and rolled down the river, eventually finding the Iapetus Ocean (the precursor to the Atlantic).
There it settled to the seabed -- near the modern New York/Vermont border -- and was buried deeply by more & more sand. After millions of years, pressure & chemicals fused it into sandstone.
Seemingly lost to time.
But the world is never still. Tectonic forces grind plates past each other, into each other. Oceans widen, oceans shrink. By 450 million years ago, large land masses were closing in on North America’s east coast. They squeezed the Iapetus Ocean, to death. As the seabed buckled, our grain of sand -- locked in its sandstone -- suffered under incredible pressures and heat. It bent, folded, and turned into a metamorphic rock called quartzite.
This rock rose, along with the rest of the newborn Appalachian Mountains, as North America slammed into Africa and Eurasia. By 250 million years ago, Maine existed as dry land. But it was in the middle of a huge supercontinent, Pangea!
The Appalachians towered as high as the modern Himalayas. Our grain of sand, now 1 mile up, was still buried by another 2 miles of material above it!
~200 million years ago, the same forces that pulled the continents together started to tear them apart. But they tore apart further to the east from where they had been welded.^ North America separated again from Africa and Europe. And Maine was part of it, its coast lapped by waves from the brand-new Atlantic Ocean.
(The Atlantic Ocean is still widening. Every year Maine gets about an inch further from Europe, thanks to the mid-Atlantic Ridge.)
Our tiny grain of quartz now lay 100 miles away from Maine's new coastline, still trapped high up in the Appalachians. Over the eons, erosion whittled the majestic range to low humps, and our seam of quartzite was exposed. But quartzite is tough. It resisted further erosion, and our grain of sand remained locked tight.
Then, 1.8 million years ago, the glaciers began arriving. 20,000 years ago, they reached their greatest extent, covering Maine in a mile-high wall of ice!
That glacier’s terrible weight dragged, ground, and pulverized the rocks beneath. It rode up and over the mountain holding our sand grain. It scoured the surface, freeing & carrying off the little fleck of quartz. 10,000 years ago, when the glacier finally receded, the sand grain lay 50 miles west of the coast in the Saco Valley, amid a heap of “glacial till” 500 feet deep.
Since then, the Saco River has steadily carved away this debris. 200 years ago the sand grain fell into the river, and traveled the last 50 miles to the ocean. The ocean then tossed it up onto a local beach. Where maybe you’ll scoop it up. Along with 10,000 other grains with their own tales to tell.
It’s a remarkable thing, holding half a billion years in the palm of your hand.
* The oceans already teemed with life, but there would be no life on land for another 150 million years!
Visiting a Maine beach in March 2010, Harold Johnson was shocked by the ocean-borne debris left by recent storms. He grabbed a garbage bag and a camera, and hasn’t looked back.
Since then he has spent most of his free time studying marine pollution, coastal ecosystems, and the mysteries and science of ocean and shore.
Copyeditor and writer by trade, historian and archaeologist at heart, Johnson’s philosophy is simple: Dig below the surface, travel the currents, make the connections, learn. Then share what you learn. He lives in Saco with his wife and young daughter. Follow on Twitter @FlotsamDiaries.