Stop ignoring rocks

Most of us don’t think about rocks very often. But we should.

Why? Because they’re cool. Literally cooled down magma from deep inside the planet, sometimes crystalized, sometimes squished and bent, sometimes ground up into dust and reformed.

But also cool for this reason: if we want to know anything about this planet we live on, rocks can quietly tell us. That’s because they’re the only things––not trees, not mice, not us––that can outlast what the earth throws at them. And life on earth can be beyond tough.

To get metaphoric, the layers under our feet are a book recounting the dramatic story of our planet, written in rock chapter by chapter from our violent beginnings pummelled by city-sized asteroids, through endless continental roaming and smashing, through land and oceans rising and falling, through endless winters and summers. And the stony story continues today.

Adrift on earth

Here’s an excellent YouTube animation by Algol that will help you picture this whole geology thing: 3.3 billion years of continental drift. Don’t worry, the action is packed into 4 minutes. Go watch it now!

Did you watch it? If so, you probably noticed that continents aren’t just sliding a bit one way or another. Over earth's history, they've roamed endlessly and widely around the planet like cereal bits swirling around in a bowl of milk, violently colliding to form supercontinents and breaking apart again, only to crash and form the next supercontinent in a completely new way. Okay, the crashes are very slow, we’re talking millions of years, but the results are big: Mount Everest big.

A very worldly capital

Watching this epic re-enactment, you may also have realized that the idea of “here” is very abstract, since the rocks under us in Canada’s capital region have been almost everywhere else on earth at some point in the planet’s 4.5 billion years of existence.

So what do the rocks under Canada’s capital region say about our world and what happened ‘here’ long, long ago? Quite a lot, as it turns out. This region has been by turns:

• pocked with volcanoes

• raised as high as the Himalayas

• squashed and scoured under kilometres-thick ice sheets

• drowned under warm equatorial seas

• dropped a full kilometre along a double fault

A lot of drama, but also: a lot of time

Today, rocks in Ottawa-Gatineau give us glimpses into a billion years of deep time, about a quarter of the history of this planet. But we also see (or rather don’t see) some huge gaps of missing time.

Of course no region will have a complete record of earth-time visible at the surface. Much of the geological record is buried deep below us, and only boring down through rock (which the Russians did, for 12 km) can reveal what’s there. The most you can hope for at the accessible surface (and in excavation sites) is a few windows on the past, and the capital region offers just that. Here we can see rocks from three main eras:

1. 1 billion years ago, a time when bacteria was the only living thing (Proterozoic eon)

2. 450 million years ago, when complex life meant snails (Ordovician period)

3. 12,000 years ago, when fully evolved humans hunted by the retreating ice sheet using gorgeously-carved and hyper-tuned stone tools like atlatls (Holocene epoch)

Combine old age and variety with some rocks that were actually created by bacteria, and Ottawa-Gatineau is a geologist’s paradise.

A picture to help us picture

Okay, there were a lot of terms in that last section that at least I didn’t remember from my last geology class ten thousand days ago. Here’s a handy graphic from the excellent Geoscape Ottawa-Gatineau by J. M. Aylsworth and others from the Geological Survey of Canada. On the left you see all the geological time periods, and on the right are those represented in this region’s rocks. We’ll talk about those gaps of missing time in Making gneiss and Sea snails and sediments.

Not actually a secret

So the history of the earth is not actually a secret; it only feels that way for most of us who don’t think much about how that boulder sitting on the lawn arrived there. But now that I’ve relearned some basic geological facts, thanks to the internet’s many passionate geologists, I can tell you that these stories are fascinating and, as always, way more complex than we can imagine, because earth is really, really old.

Over three posts (Making gneiss, Sea snails and sediments, and Just yesterday) I’ve tried to lay out the broad strokes of capital rocks: what was happening during those three time windows and why the rocks turned out the way they did. After reading these posts, you may never look at a pebble, slab, or outcrop without wondering how it came to be. And I am truly sorry about that.