Ancient Shore

The following is lightly edited from notes written last week, as I travelled westward on a flight from Fredericton to Toronto.

Across northern Maine and southern Québec, those ever-changing landforms are ghosts and memories. We cannot say that the Earth remembers everything that has ever happened to its surface – it has forgotten far more than it remembers, but it remembers a lot.

Every one of those features below us has a memory to tell, the story of how it was formed and how it changed through time – some of them are rich memories, full of detail and arc of story. Others are faded wraiths: you might just make them out if you look at them out of the corner of your eye, but they disappear when looked at straight on or in bright sunlight. Perhaps the dark arts of remote sensing, isotope analysis, and X-ray diffraction will divine their stories, but they hide their secrets deeply.

Wind generators on the Appalachians, along the Québec-Maine border near Lac Mégantic

So many features, and so many of them are scars. Earth has had a long history of damage and injury – some of the injuries have come from outside, but some have been self-inflicted. Poor thing, our old Earth. We need to understand it better and treat it far better.

Walking with my brother earlier today, we compared injuries and war wounds – a chronically sore ankle here, an arthritic hip there. We commented that the human body might appear to heal, but it still carries the scars and damage within itself. That damage can rear up and reveal itself at some later date –  if we had known what we know now, we would have been more careful decades ago when we hurt ourselves.

Lac Mégantic

Earth is like that, too: many of its scars are not obvious to most of us. Those Appalachians we just passed over are one such scar – they tell us how tectonic plates crashed together oh so many years ago (starting about 480 million, actually), when Laurentia, the ancestral heart of North America, began to push into the crust of the ancient Iapetus Ocean (the continuation of this would eventually lead to the formation of Pangaea, as Laurentia pushed into northern Africa). In the process, Earth’s crust was buckled and pushed up into mountain ranges that, at their highest, may have been as tall as the Himalayas are now. Even Mount Katahdin, at a full mile high (including the cairn on top), is just a low remnant of those mountains. What happened to them? Earth may have self-harmed through plate tectonics, but it has been self-healing ever since through the use of weathering and erosion.

Earth started self-harming early on, apparently as a result of poorly resolved heat issues deep within. Plate tectonics began billions of years ago. The plates slowly move from one self-inflicted scar to another; the new crust rises at spreading centres (divergent boundaries) such as the mid-Atlantic Ridge, and crust is subducted and melted at convergent plate boundaries such as that along the Aleutian Islands. The scars are long and jagged, extending all around the planet’s face.

The sediment of the Saint Lawrence Lowlands plain is cut by rivers. Note the characteristic Québec field pattern, with long narrow fields extending away from the waterways.

You might argue that Earth is not really self-harming, that plate tectonics is nature’s course, and just the way a planet has to be. But other terrestrial planets aren’t like this. They have managed to grow up without plate tectonics (like Mars?), or they may have experimented with plate tectonics in their early years (like Venus), but later outgrew this juvenile deviance.

And sure, Earth self-harms, but at least that self-harm prevents it from showing many scars of external violence, unlike the Moon and Mars. All these bodies have been bombarded by meteorites, comets, and other space debris, most notably in their formative years – they all had a tough childhood. Earth’s self-harming may have allowed it to overcome that childhood damage – the scarring from plate tectonics effectively hides most of the pitting and damage from that external violence, except for a few places like the Manicouagan crater (which isn’t all that far to the northeast of us here).

Mont Rougemont, rising out of the Saint Lawrence Lowlands, is one of the Monteregian Hills. These igneous hills, which include Mount Royal and mont Saint-Hilaire, were formed as North America slid over a “hot spot” during the Cretaceous Period.

Now we are out over the flat Saint Lawrence Lowlands. We could consider this sort of sediment-covered plain as being a “fully healed” patch of the Earth. The sediment has accumulated on and off over the past 500 million years or so. It blankets and hides the far less regular terrain beneath, including Logan’s Line where Appalachia and the Canadian Shield butt up against one another. Even below all that sediment is a scar that has never quite healed, as evidenced by the earthquakes that have occasionally struck Québec during the past few hundred years.

But wait. I can see some fresh wounds down there. Erosion never sleeps, and those valley sediments, even the relatively recent ones deposited under the Champlain Sea  some 10,000-13,000 years ago, are cut by fresh narrow rivers that knife through the surface and carry away the clay and soil.

Montreal and the Saint Lawrence River

Flying over Montreal, we see some of the most recent of Earth’s cuts and scars. But these are not self-caused; rather, they come from a parasitic infestation. The deep slicing of the St. Lawrence Seaway, the piling of stone on the side of Mount Royal, the piercings constituted by the Lafontaine Tunnel: these are not Earth’s own doing.

Will Earth’s scars and damage ever heal?  With enough weathering and erosion, all those hills would be flattened, rock fragments and clay would be transported away by rivers, and the entire surface of the planet would be a nearly level plain, probably located somewhere below sea level. But fortunately for all life, that won’t happen, because there is no evidence that Earth will ever cease self-harming. Even as I write this it is creating new crust along the ocean ridges, and pushing the Himalayas just a little bit higher. We can rest secure in the knowledge that tectonism never sleeps.

The blue arrow shows the approximate route of the plane over southern Québec. (based on Google map)

© Graham Young, 2016