Mad About Science: 7B before people

By Brenden Bobby
Reader Columnist

I first learned about the Great Missoula Floods when I was in elementary school in the ’90s. I listened in wide-eyed wonder to my teacher describing the events of the floods: massive walls of water once held back by the Missoula ice dams unleashed to rip through the entire Pacific Northwest. What it must have been like to stand on the top of Schweitzer and watch mountain-sized tidal waves of ice and water come roaring through the basin and carve away the dirt and stone to create the fifth-deepest lake in the United States.

It’s easy to think that this place has always looked this way, with a big, beautiful lake and conifer-covered mountains as far as the eye can see, but Bonner County’s current configuration is relatively recent. Our wonderful lake is only around 18,000 years old, barely a fledgling puddle compared to Lake Baikal in Siberia, Russia, which is believed to be at least 25 million years old. What did home look like throughout time? Before the lake was here, before the first Indigenous peoples ever set foot here, before the dinosaurs roamed the Earth?

It’s important to know that talking about locations across such huge spans of time is difficult. Continents by their very nature move. Huge oceans of molten rock in the Earth’s mantle are constantly in motion. Massive glaciers etch away dirt and stone, and deposit them elsewhere. Precisely tracking where this tiny area was throughout prehistory becomes difficult and problematic. Are we tracking a coordinate, a single stone or a precise amount of acreage?

Most geological tracking has been done by approximating locations of tectonic plates aided by computer simulations, which are supported by fossil and geological evidence. Basically, if we found a fossil of a mollusk from 200 million years ago, that means this area was underwater at one point or another. Based on our own measurements of how the continents have moved, however slightly, we’re able to project how they shifted and moved across hundreds of millions of years.

Taking that into consideration, let’s take a trip back in time.

The location that would become Bonner County in 1907 has moved considerably throughout the geological history of Earth. The vast majority of time was spent under the ocean, particularly when the Earth was hot. Even more curious, our area was quite close to the south pole for many hundreds of millions of years. Throughout the Cambrian Period, around 500 million years ago, the continent that would eventually become North America was far to the south. Our area was part of the shallow ocean at this time, and likely stayed this way until around 240 million years ago, when we were a part of the western shore of the Pangaean supercontinent. What would become Bonner County was remarkably close to both the equator and the ocean, as what would later become Washington state hadn’t quite formed yet. This was the beginning of the Triassic Period, which was the apocalyptic beginnings of dinosaurs on Earth.

The climate of the early Triassic was harsh. Earth was dry and hot, with limited rainfall and arid conditions across most of the planet. Just 20 million years before, Earth suffered its greatest extinction event ever — the so-called “Great Dying” of the Permian-Triassic cusp — which wiped out an estimated 90% of all ocean life and 70% of terrestrial life on the planet, including a number of plants that had helped to regulate climate conditions by manipulating carbon and water. As the world continued to warm, life evolved to adapt and Bonner County sank back beneath the ocean.

About 200 million years ago, at the end of the Triassic, another mass extinction occurred. This was the period when dinosaurs first began to dominate the Earth. The planet cooled, oceans receded and this area may have had some actual beachfront property for a few million years.

Through the Jurassic Period, 199 million years ago to 145.5 million years ago, our area stayed above water. The planet was warm and wet, as vegetation flourished and dinosaurs grew to enormous sizes. Our area was likely a basin ringed by large mountain ranges, while everything from Montana eastward was beginning to resemble the North American continent we’re familiar with today.

Earth grew warmer for the following hundred million years as the Jurassic became the Creataceous. Dinosaurs would continue to dominate the North American continent until one fateful day about 65 million years ago, when an asteroid with a diameter equal to the size of Kootenai, Sandpoint and Dover combined, smashed into Earth at Mexico’s Yucatan Peninsula.

This was a bummer for the dinosaurs, but it worked in our favor. Earth cooled due to the massive debris cloud and smoke from global forest fires, throwing the planet into a series of ice ages that would alternate between phases of cold and warm.

While the continent itself didn’t go through any giant changes like Pangaea, it’s undeniable that this area must have changed dramatically throughout the past 65 million years. The repeated heating and cooling of ice ages and the tremendous eroding force of water altered the landscape an untold number of times until it finally appeared to us as it does today. Even now, if you look closely enough, you can see the scars of glaciers pushing through the mountains like a garden trowel through soil. 

The first humans set foot in North America during one of the glacial periods 20,000 years ago. This means the ancestors of the Indigenous peoples were present on the continent when Lake Pend Oreille was first carved from the basin. I’d like to imagine that someone, somewhere, must have witnessed one of these great floods, perched safely upon a mountaintop bundled in furs to see the cataclysmic birth of Lake Pend Oreille.

Unfortunately, it was probably way too cold for anyone to be here for that, so that awesome splendor remains a secret kept between the stone and the sea.

Stay curious, 7B.