Stoked on Science: The Rocks of Revelstoke-Freeze, melt, snow

Jade Harvey

Special to the Review

Right now, for most of us, the longest time span we can envision going forward is getting through Christmas, the holidays and into the New Year.

Looking back, the mild November seems so long ago, with streets blanketed in snow and brightly coloured lights dotting the yards in the neighbourhood.

I am going to ask you however, to throw your thoughts back 2.6 million years — if you ask a geologist, basically yesterday — in our Earth’s history.

It is called the Quaternary period, a supremely important time where our world begins to resemble the one we see today.

It covers the emergence of humans, the development of our current glacial and interglacial (warm) periods, the arrival of our continents to their current position and the resulting ecological zones.

Scientists believe that the Rockies may have stood six kilometres tall after the second mountain building phase, 125 million years of layers of accreted or scraped up rock.

The modern landscape is a result of differential erosion between soft and hard layers of the accreted rock.

The soft layers were worn down more and became the valleys we nestle our communities in.

The hard rock, the ridges and peaks we recreate upon or simply view with admiration for their stature.

Herein lies a wonderful paradox. The Rockies and Columbias have steadily lost elevation due to erosion, but because the valleys have deepened faster, the ridges and summits lie farther above the valley floors now than they once did.

Our landscape is glacial, carved out by the up to 14 ice advance and retreats of the ice sheets and glaciers of British Columbia in the last 2.6 million years.

The most recent major glaciation occurred between 25,000 and 12,000 years before present, named The Late Wisconsinan Glaciation.

Glaciers expanded, early humans were forced south or to adapt to extreme cold and the rocks were covered with ice.

If you see jagged, sharp peaks on mountains, they escaped being submerged under ice caps or glaciers.

Smooth mountain skylines indicate they were beneath the ice surface, being polished as the ice flowed with gravity from on high.

Often in B.C. you can see, below jagged peaks, lighter horizontal lines like someone got a ruler out and traced across the face of the mountain.

These “trimlines” indicate the highest extent of the ice up the rocks.

The depth to valley bottom truly allowing to envision the magnificence of a landscape once filled to the brim with ice.

In the middle of the Quaternary period, something significantly changed in the way our climate interacts with the suns orbital forcing — that is to say the way our movement around the sun impacts on our climate.

Before 1.2 million years ago, our climate worked on 41,000 year cycles with less fluctuations and thinner ice sheets. After the Mid-Pleistocene transition around 1.2 million years ago, our climate began to wax and wane on 100,000 year cycles creating higher amplitude changes that have resulted in the huge changes between cold and warm temperature that we see between the last ice age and our warm climate today.

So how do we know this? One way is from deep ocean sediment cores.

All elements on Earth exist with different isotopes. This is basically the mass of an element depending on how many neutrons it has in its atom nucleus or centre.

You might have heard of carbon 12 or carbon 14, oxygen has three main stable ones — O16, O17 and O18.

When water evaporates from the oceans and locked up in ice it has more of the lighter (lower number) O16 isotopes. The heavier (higher number) isotopes remain in the ocean.

Sediment that falls and settle to the bottom of the ocean records the ratio of these different isotopes.

Thus if we find sediment with more O18 its deemed a cold period as the O16 is in the ice, or if there is proportionately less of O18 in there it’s a warmer period.

This is a tried and tested way to recreate paleo or past climatic history. Its amazing to think we have machinery that can take sediment cores that span back five million years of Earth’s history from the bottom of the ocean.

So the recent times are less about rock and more about climate.

When we came out of the last ice age 12,000 years ago, the climate warmed, ice melted, water flowed through the valleys we see today and created a myriad of lakes on route to the ocean.

The wind and precipitation since has shaped our world into one of jagged peaks, flat valley floors, frost fractured cliffs and everything in between.

This landscape around is unique. Created by a set of circumstances so individual and complex scientists have been arguing about it for centuries.

As our scientific and technological advances have allowed us to test hypotheses that have been espoused for hundreds of years, it now becomes clearer how our world was shaped around us.

Revelstoke, The Columbias, The Rockies. So special. So perfect in their journey.

Billions of years to bring us to this place we call home. The rocks of Revelstoke, well, they rock.

Jade Harvey has a degree in physical geography. She owns and operates Stoked On Science delivering science and sports programs in schools across the district and through the City of Revelstoke and ACC.

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