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Hall: A bedrock connection between the Earth and the Moon

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Canada geese (lower right) flock beneath the Canadian flag at Sault Ste. Marie, Ontario, Canada.


Monday, August 29, 2016

I stand on the Canadian Shield.

It’s hot in Greenville in August. It’s not in Canada. The Canadian Shield is just right!

The Canadian Shield isn’t just coolness. It is stability. It is solidity. It is solace. In a crazy world, the Canadian Shield is a rock.

Even in an uncrazy world, the Canadian Shield is a rock. A very old rock.

Many scientists consider the it to be one of the earliest pieces of continent on the Earth. It is older than Grandpa. Older than George Washington. Older than dogs, older than dinosaurs, older than dirt. Almost as old as the Moon.

Four thousand million years ago, geologists say, the Earth had cooled enough for rain to collect in oceans and not boil away. The continents were aberrations that stuck up. Variations deep inside the Earth caused volcano bumps and earthquake jumps, making the Earth lumpy.

The Canadian Shield was one lump of island in that early ocean, and seems to have remained above water. In the billions of years since, its features have been washed by erosion, edged with new land, topped with sediments, squeezed by other continents, riddled with fresh magma, scraped bare by glaciers, and cracked by earthquakes over and over again, but the 1500-mile-wide shield of modern-day eastern Canada has continuously protruded from the sea.

In a fraction of that history, Canada is inextricably linked in my mind to the Moon. I grew up in a village eight miles from Woodstock, N.Y., which in the summer of 1969 was considering hosting a little rock concert. The Moses family had no intention of setting the sights and sounds of psychedelic songsters on its sensitive offspring. We fled to Canada.

So we were in Quebec at the greatest moment of all history. In July of 1969, a species transported itself, deliberately, from one globe to another. After centuries of human enlightenment and decades of human industrialization, on a countdown to zero that began with Galileo Galilei and ended with “one small step for man,” the United States launched a fragile-skinned, spider-bellied, fire-tailed missile on a journey of 240,000 miles across empty space to land on a hot and cold, dark and light Moon, with humans aboard. The world watched, spellbound.

We watched, spellbound, on a small black and white television as President Nixon spoke to the astronauts in French subtitles.

This year, the travel is mundane. No missiles, no astronauts, no psychedelics. We came to stand on the rocks and feel the washed and edged and topped and squeezed and riddled and scraped and cracked history.

It is tough forensics work to retrace the journey of a continent through that history, unwrapping the folds and unwinding the flows and distinguishing the wash from the riddle, and it is fraught with scientific argument, but every rock interaction leaves a distinguishing scar behind as a clue.

Determining the exact saga of a continent is like estimating the precise path of a raisin kneaded through a loaf based upon its character in today's buttery toast, using grill lines and bread crumbs, cinnamon residue and yeast bubbles, raisin wrinkles and slice patterns to guide one’s deductions. The Canadian Shield is such a raisin toasted into the Earth.

The Shield began as a blister of magma swelling from deep in the Earth, feeding volcanoes that no longer erupt or even exist. Over time, wind and rain sanded them, and the dust settled to the flanks of the Shield. Hot magma below roasted the granite, and deepening dirt overhead squeezed it, baking much of it into gneiss.

The gneiss bent and cracked from those pressures. Liquid magma seeped up through those cracks. Repeatedly, offshore volcanoes inched against the Shield. Glaciers came and went, grinding the Shield surface, and weighing it deeper into the hot mantle on which it floats.

Rivers carried dirt and rocks from upstream to downstream. Earthquakes ripped rifts and cliffs as the land stretched and squeezed. Several times, the crust froze nearly worldwide. Continents slammed against the Shield, rippling up new mountains. The Canadian Shield is a rock, but it is taffied with other rocks, a topsy turvy tumble of terra cotta firma.

Then, in 1969, humans traveled skyward from a fingery, Florida flange on the newer ledges and edges of the Shield, traveled beyond the continent, beyond the Earth, to leave a new layer of dust and dirt and debris on the Moon.

All that coolness fans a hot August day.


Joy Moses-Hall teaches physics and astronomy at Pitt Community College. She has a PhD in oceanography and is the author of the novel Wretched Refuge.