Land of Nipigon

Geological History

The first 3.5 Billion Years

Dust, swirling and coalescing in space. That’s how the earth starts. The dust is remnants of an older star system long since gone and reduced to the dust and rock. Something causes the dust and rock to start to consolidate into larger and larger pieces, like a snowball rolling down a hill, gathering more and more dust and rock as it goes. After aeons, the dust ball is so large and generates so much heat that it melts from the inside out. Welcome to earth.

Still bombarded by dust and other larger chunks, all the material that makes up the planet and the life was deposited billions of years ago.

As the earth cooled from the outside forming a thin crust, the heat from inside the earth was constantly melting it and ejecting it to the surface again. Every time the newly formed crust would melt, some of the heavier stuff would sink, leaving the lighter stuff on top. Over and over this would happen until the lighter material formed solid islands, floating on the sea of molten heavier rock.

Heavier rock started sinking under the lighter rock, we now call that subduction and it is the basis for plate tectonics today. As today, areas where one rock “plate” subducts under another we have volcanoes and earthquakes and a highly dynamic margin referred to as an island arc. Over time, the volcanoes spewing forth and subducting fundamentally changed the rock as every time it melted it lost a little of its heavy stuff. This newer, lighter rock is what make up the continents today, with the more massive rocks making up the ocean floors.

Ocean floors are made of heavier materials which are darker to the eye, called mafic rocks. Continental rocks tend to be both lighter physically and visually; we call these felsic rocks. All the rocks float on a semi-molten, almost plastic type layer of rock which allows the solid rocks above to flow and move.

As the lighter continental rock floats around, they begin to interact with other islands of continental rock. When two chunks of continental rock meet, they tend to stick together and build huge mountains. As they make mountains, the form deep roots, thickening the crust even more, which in turn collects and combines with more continental crust. These are the first true continents and are the oldest surviving rocks on earth. We refer to them as continental shields, and they are thick, stable and old chunks of rock which are very hard to break apart.

Continental shields make up the core of all the continents of the earth. North America, South America, Africa, Europe, Asia, India, Antarctica and Australia all have shield rocks at their core.

Today the continent of India is colliding with Eurasia, and the results are the spectacular mountain ranges of the Himalaya’s and Mount Everest itself. This gives you an idea of scale on how big the mountain chains that were created when the shields came together.

When travelling the Canadian shield, you are walking/driving on the roots of ancient, great mountains.