Saturday, April 11, 2015

Through the Past and into the Future: A View from the Harpswell Cliffs

The cliff walk in Harpswell lives up to its name. The trail makes a turn and dumps you out on a view worth far more than the effort required to hike to it. While it didn't take me long to reach the top of the 150 foot cliff, the rock itself would have taken far longer to make the climb. The rock is schist - the glittery remains of mudstone that has been crushed and baked in Earth's oven. The mud itself piled up in some prehistoric ocean bottom, perhaps at a rate of a foot every thousand years. Peering down the 150 foot cliff to the estuary below, I imagined a stream tediously cutting through millennia worth of deposition, time traveling further and further into history. This erosion might open a window into a time period 150,000 years before the rocks on which I stood formed. As it turns out the chasm was a portal through time, but the time machine traveled into the future.

Around 490 million years ago, a slab of continent we call Avalon near the South Pole cleaved itself from its parent, a supercontinent called Gondwana.  As it journeyed northward it developed a predictable series of layers.  An early layer became our cliff. Not long after it left the Antarctic Circle mud rained down on the ocean floors of the microcontinent's coast. It accumulated for that 150 thousand years and longer.  As the microcontinent scrolled past 40 South, 445 million years ago, volcanoes laid new rock on top of old. This was, in turn, buried by ocean bottom. The new ocean floor was topped by one final, explosive, volcanic eruption, the icing on a layer cake of rock that was a testament to the long journey. 

A lot went on to make the Harpswell Cliffs time portal.
First the layers of rock were laid down flat (with the
schist of the cliffs in blue and the volcanic rock across
the estuary in red).  Then the layers cracked and stacked.
Next they bent into wavy layers.  Finally the tops were shaved
off by erosion, exposing our cliffs and the peninsula below.
In an orderly world, where progress is constant, it is obvious that the rocks of the Antarctic circle would never be seen again. Instead they would be buried deeper and deeper. But these rocks lived in a world where journeys end. The unstoppable northward force would eventually meet its harbor, the immovable North American continent. This collision was massive. Pieces of continent were flung and tumbled, like ice onto a spring shore.  Avalon cracked and its parts were thrust on top of one another.  Now it was that final explosive eruption, the icing on the cake, that had been interred by its own past.

The compression of this part of the Earth continued. The heat and pressure of the collision would transmogrify the fine grained mudstones into glittery schists. The layers would flex into a washboard of ridges that make southern Maine's coastal islands and peninsulas so multitudinous, lifting the schist of those cliffs to their present height and higher.  The problem was that gravity abhors a ridge. Ice, water and good old falling did their best to even off the tops of the rolling ridges. Sanding of those tops meant revealing the bowed edges of the cake layers.  

It may have been a glacial flood, a stream funneled by a weak layer of rock, or just plain luck that cut through those last 150 feet. Whatever it was gave me a window through one hundred and fifty thousand years of mud to a blue estuary below. Looking across the water revealed not a predictable past, where time moves ever forward. Instead, I looked into an explosive future where, given enough time, the world could be turned upside down.

Liu, Dennis. Earthviewer. Computer software. Vers. 1.1. Howard Hughes Medical Institute, Jan. 2013. Web. 11 Apr. 2015

Hussey, Arthur M., and Henry N. Berry. Bedrock Geology of the Bath 1:100,000 Map Sheet, Coastal Maine. Augusta, Me.: Maine Geological Survey, Dept. of Conservation, 2002. Print.

Druyan, Ann, and Steven Soter. "The Clean Room." Cosmos: A Spacetime Odyssey. Fox. 20 Apr. 2014. Television.

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