By Rick Guenther, © 2001, All Rights Reserved
Somewhere on the plains of the Peace Region many eons ago, a ten-meter long bipedal dinosaur bends down to grasp some succulent willow leaves and shoots with its broad mouth. With a quick jerk of its head it breaks the foliage away and begins to munch nervously, its jaws grinding the leaves and stems between large teeth.
Frequently it lifts its head to smell the air while its eyes scan the nearby forest depths for any sudden movement. Tenontosaurus, similar to duckbill dinosaurs, has reason to be wary for it knows what every herbivore knows. Where there are plant eaters there are also carnivorous predators, which in this age developed into the most fearsome the Earth has known. Hidden in the shadows of nearby coniferous trees lurks a pack of Deinonychus, models for the raptors of
Jurassic Park fame. Less than a meter and a half tall, these small dinosaurs made up for a lack of size with speed and the “cutting edge” armament of the day. On each foot one toe was equipped with a long sickle shaped claw specifically designed for the purpose of slashing raking wounds in prey. Deep, meter long slices, inflicted by a pack of these animals, were capable of bringing to earth creatures much larger than themselves.
With some noiseless signal, pack members are alerted to the presence of the lone herbivore and with blinding swiftness, they attack. In its vain attempt to survive. Tenontosaurus whips its long tail, toppling some of its tormentors and stomping others. But the numbers are too great. In seconds the hapless herbivore is surrounded, and in spite of a valiant struggle, is reduced to bloody shreds, a meal for the hungry carnivores.
While this image of the Earth’s past has been popularized by Hollywood, it nevertheless represents a plausible event in the history of the Peace Region. In that distant past the Rocky Mountains were still infants continuing to grow. The continent of North America was situated in warmer latitudes and the Peace Region consisted of broad, lush deltas feeding a shallow inland sea.
The geologic history of the Peace Region begins much earlier, however, and properly begins with the origin of the Earth, approximately 4600 million years ago. Condensed from a vast cloud of dust and gas, the primordial Earth was more like Dante’s vision of Hell than any environment existing today. Heat, from gravitational collapse, turned the young planet into a molten cauldron of minerals and elements surrounded by an atmosphere of predominantly hydrogen and helium. Planetesimals, bits of this and that left over after the planets and sun formed, plunged through the atmosphere for the next several hundred million years maintaining temperatures which kept the Earth a fiery liquid. Eventually this cosmic rain abated and the Earth began to cool allowing islands of rocky crust to form. These islands enjoyed only an ephemeral existence however. The liquid mass underneath churned and the islands were consumed like macaroni rolling in boiling water. Approximately 4100 million years ago, temperatures had fallen enough to allow the entire outer layer of the Earth to solidify forming a crust which floated on a mostly molten layer below, the Earth’s mantle. Water, outgassed from the Earth’s interior by volcanoes and imported form space by comets, accumulated in the low lands as the world’s first oceans. Continued cooling increased the thickness of the crust and changed the mantle below from liquid to a plastic state, not quite solid but soft enough to flow in huge convection currents. Driven by the energetic currents in the mantle below, the Earth’s crust was broken into a vast number of rigid plates similar to the cracked shell of an egg.
There are three types of boundaries between these tectonic plates. Plates can separate or rift, they can collide or converge and they can slide horizontally past one another. This plate tectonic activity causes volcanoes and Earthquakes, raises mountains and changes the Earth’s surface like a jigsaw puzzle whose pieces change shape each time they are connected. As time passed, small slivers of continental crust collided, stuck together and formed larger masses which became permanent fixtures on the denser rock below. These welded assemblages of ancient crust, called cratons, form the cores of present day continents.
About 4 000 million years ago, the Earth’s surface had cooled enough for water to remain liquid and shortly after, the first life-forms appeared. The oldest fossils known are those associated with primitive, single-celled marine organisms. Found in Canada’s northern lands, these 3800 million year old rock records indicate that life had gained a foothold on Earth very soon after the first crust had solidified!
The first cells were probably similar to varieties of bacteria living today in the dark ocean depths. Along rift zones, where magma lies close to the surface, the crust is fractured allowing sea water to infiltrate. As the water flows near the magma its temperature rises, increasing its ability to dissolve minerals, and when it returns up to the sea bottom it exits from vents at temperatures of several hundred degrees Celsius. When this mineral laden water mixes with the near freezing sea the minerals precipitate producing clouds of fine particles. This mineral soup feeds colonies of bacteria who obtain their energy from the inorganic compounds. Like green plants on and near the Earth’s surface, these bacteria serve as the primary producers, converting inorganic into organic compounds which become food for the other animals which live in the dark isolation of the ocean depths. Eventually the forces of evolution modified some of those ancient bacteria, equipping them with the biochemical machinery to use sunlight as a source of energy. In this process of photosynthesis carbon dioxide is converted into carbohydrates and oxygen is released as a waste product. When these photosynthetic cyanobacteria first appeared, the atmosphere was predominantly carbon dioxide with little or no oxygen. For at least three-quarters of the Earth’s history these humble organisms remained one of the dominant life forms, gradually modifying the atmosphere and preparing the Earth for all of the oxygen consuming creatures which followed.
While single-celled organisms dominated the biosphere, geological forces continued to change the physical features of the planet. As the internal heat of the Earth radiated away into space, the energy and speed of the huge convection currents in the mantle decreased but they continued to push and pull the crustal plates above. Small landmasses collided creating supercontinents to be torn apart later in a global cycle which persists to the present. At least four supercontinents have appeared in the Earth’s history but only the origin and fate of the last one, Pangaea, is well understood. Plate tectonic activity tends to destroy geological evidence so only recently has some comprehension been gained of Pangaea’s predecessor, Rodinia.
Approximately 1100 million years ago Rodinia had been assembled with ancestral North America at its core. Evidence suggests that for several million years the centre of Rodinia, including the western part of North America, was covered with a shallow inland sea. The processes of erosion ground down surrounding mountain ranges and wind, water and ice transported the sediments to the sea floor. Sands piled up near the shoreline, myriad cyanobacteria grew in slimy mats secreting limestone in the shallow waters nearby and further out, in deeper water, muds accumulated. At least 8000 m of these sediment layers, which geologists call the Purcell group, eventually turned to stone.
Subsequent uplift of the continent above sea level allowed erosion to remove some of those sedimentary rock strata but a substantial thickness remains, resting on the ancient craton several kilometers beneath our feet. Life, during Rodinia time, remained primitive. Single-celled organisms still dominated, living in the oceans and possibly in ponds and pools on the barren land. No vegetation existed to colour the harsh landscape. Nothing flew or walked or crawled over the rocks of dry land. The only sounds would have been those created by physical phenomena such as winds howling over sharply sculpted outcrops, water gurgling along serpentine channels carved into bedrock or waves crashing onto a beach. No fishes swam in the seas and no lobsters scuttled along the ocean floor.
Not until 600 million years ago, after 85 % of the Earth’s history had passed, did multicellular life appear. Approximately 800 million years ago the convection currents in the Earth’s mantle shifted and changed directions. Tensions in the Earth’s crust broke Rodinia apart along rift zones, one of which separated North America from the landmass to which it had been attached. North America’s new coastline extended roughly along a Northwest-Southeast line through the middle of what is now British Columbia. In the process much of the rock which had accumulated in the inland sea of Rodinia was ripped away leaving remnants only in the southern and northern ends of the Rocky Mountains. Geological field work completed over the last couple of decades has finally discovered the identity of the missing continent to which British Columbia and the North-West Territories had been attached. We call it Australia, mate!
During the process of rifting the western margin of North America became thinned and torn, resulting in a broad but chaotic coastline. Huge blocks of crust tilted and slid along faults and, where their summits broke the ocean surface, appeared as islands. Rivers now found easy paths to the sea, rapidly eroding the rocks of the continent’s interior and depositing the sediment in the submerged canyons and plains off shore. For approximately 200 million years sedimentation continued, eventually producing a sequence of rocks at least 8 kilometers thick. This sequence, referred to as the Windermere group, rests on top of the remains of the Purcell group.
After the breakup of Rodinia, the North American plate began a slow march north until it straddled the equator 515 million years ago. Our “West Coast” then faced north and the Peace Region occupied a broad plain, flattened by eons of erosion, on a shoreline which roughly followed the present boundary between British Columbia and Alberta.
Over the next hundred million years the shore line advanced and retreated across the Peace Region, inundating western Canada as far as eastern Saskatchewan. In shallow waters cyanobacteria and primitive sponge-like creatures secreted limestone, building reefs while muds accumulated in the depths around them. When the sea advanced, water depth increased killing the reef builders and they became buried in sand and mud. Cycles of advance and retreat thereby constructed the layer cake of shale, sandstone and limestone which comprise the bedrock of the Peace Region.
Geologists divide the Earth’s history into time intervals based primarily on the types of life which existed, as indicated by the fossil record. Until 544 million years ago life on Earth remained primitive, consisting of single celled organisms and some soft bodied worms and jellyfish like animals. Rocks younger than 544 million years reveal a far greater diversity of life and are divided into three eras, the Paleozoic (544 – 245 My), the Mesozoic (245 – 66 My) and the Cenozoic (66 My – present).
At the beginning of the Paleozoic era remarkable changes in the Earth’s living community were taking place. For a few million years a rapid diversification in the variety of life forms occurred, with the appearance of most of the major biological groups known today as well as several which have long since become extinct. Familiar and bizarre forms populated the oceans of the world although no life, plant or animal, had yet made the transition to dry land. This explosion of life is nowhere better exposed than in the Burgess Shale of British Columbia’s Yoho National Park. Discovered just past the turn of the century, the stone in this small quarry, perched high on a steep slope between two mountains, has yielded thousands of exquisitely detailed, 515 million year old fossils of both hard shelled and soft bodied animals. At the base of an underwater cliff less than two hundred meters high, unusual conditions favoured the preservation of fine structures of muscles, organs and skin of the hapless denizens who were swept down from the shallow seas above. Almost all of these creatures were one to ten centimeter long invertebrates with the occasional monster reaching as much as a meter in length. While these spineless animals dominated the waters there was at least one small, seemingly insignificant creature which coexisted, biding its time, waiting for its moment in the sun. Fossils of a small, centimeter long swimmer show the rod like structure in its back and the V-shaped muscle bands characteristic of vertebrates. Possibly the descendants of this humble animal now gaze with wonder on its delicate remains.
Around 425 million years ago the Earth’s crust, with its icing of sedimentary rock, bent gently upward along a line just east of the current boundary between British Columbia and Alberta, possibly due to the continental collisions which had begun sometime earlier far away on the east coast of North America. This West Alberta Ridge extended as far north as the Peace Region and as far south as Montana, forcing the ocean to enter western Canada’s shallow inland sea from the north.
The tropical location of North America resulted in warm seas, fostering a wide variety of life. For the last 100 million years evolution had worked its magic and animals with internal skeletons and backbones joined the invertebrates in the oceans of the Earth. Possibly one of the groups of small eel-like animals of the Burgess Shale, over countless generations, evolved into the diverse collection of fishes which now existed. In this time period sharks appeared, many with bizarre appendages unknown today. Their basic form has remained essentially unchanged making them one of the longest lived animal groups known. More importantly for us, some fishes developed rudimentary lungs which allowed them to creep out of the oceans for brief periods of time. These ancestors of the amphibians became the first vertebrates to venture onto dry land, although they were not the first animals to leave the seas. They were preceded by invertebrates, such as insects, who were the animal masters of the terrestrial environment. But before any animals could gain a foothold the land needed plants, the only organisms capable of harnessing the sun’s energy to produce food. For plants, this posed a formidable challenge. Surrounded by water, aquatic plants were in intimate contact with necessary nutrients and did not require strong structures for support. In order for plants to exist out of water, they needed to develop interconnecting cell walls for support and ultimately a vascular system to transport water and nutrients from the soil. This transition occurred more than 400 million years ago and shortly after the Earth was covered with shades of green.
While life was thriving in the sea and on the land, the land continued to change. Erosion removed the rock of the Alberta Ridge until it was completely submerged except for an island at its northern end, the Peace River Arch, which persisted for a few million years more. The sea advanced and receded several times across the broad shallow coast and each recession left huge lakes which evaporated in the hot climate leaving behind thick deposits of salt. Covered and preserved by layers of sediment these buried salt deposits are now mined commercially in Saskatchewan.
The warm shallow waters also promoted the growth of a variety of limestone secreting organisms. The most abundant of these were stromatoporoids which created porous, sponge-like skeletons. As they grew, their limestone skeletons joined together to construct huge reefs which surrounded the Peace River Arch and extended across the inland seas covering western Canada. Eventually, conditions grew unfavourable for the reef builders. A rapid increase in water depth followed by an influx of sediment buried the reefs and killed the stromatoporoids.
In the thick mud on the sea floor, organic oil, the product of countless dead algae, was squeezed through permeable strata to collect in the reservoir created by the interconnected pores left by the stromatoporoids. In time, heat and pressure converted these organic compounds into crude oil and natural gas. Today we drill down through kilometers of sedimentary rock to tap this ancient resource, thanking the tiny organisms who laboured unwittingly on our behalf. From 475 to 245 million years ago western North America remained tectonically quiet, a “passive margin”. The Earth’s tectonic plates continued to move but the collisions which create mountains occurred elsewhere. The sea advanced and retreated many times over this passive margin, allowing erosion of exposed rock when it was gone and deposition on its floor when it returned. In this way a layer cake of sedimentary rock was gradually constructed on top of the craton underlying western North America.
Unbeknownst to the creatures of the Paleozoic era, a catastrophic change was about to take place, an event or events which would eliminate more lifeforms than any other in the Earth’s history. While the exact nature of the catastrophe is not yet known, some action or process caused the extinction of 95% of all existing species of life! Causes may include rapid changes in climate, a drop in sea level allowing detrimental chemical reactions between the exposed sediment and the atmosphere, diseases, volcanic outbursts or cosmic collisions. The discovery of the Chixulub impact crater in the Yucatan peninsula of Mexico, which is widely accepted as the great terminator of the Mesozoic era, certainly supports the last possibility.
The Mesozoic era, extending from 245 million to 66 million years ago, began and ended with major extinctions. This, the age of dinosaurs, represents a time period in which western North America changed from a relatively flat and quiescent continental margin into the mountains and foothills we see today. Near the beginning of the Mesozoic all of the Earth’s continents had again been
assembled into a supercontinent, Pangaea. North America had become attached to Pangaea along North America’s eastern coastline and the collision resulted in the creation of the Appalachian mountains. The west coast of North America now actually faced west over the global ocean, Panthallassa. Near the end of the Paleozoic era sea levels had fallen and they remained low for the first part of the Mesozoic. Prevailing winds blew hot air from the east over the dry interior of Pangaea making most of North America a desert. While the winds eroded the exposed rocks and piled the sand into dunes on the land, rivers carried their share of sediment into the oceans, adding them to the older rocks on the wide continental shelf.
About 210 million years ago Pangaea began to break apart, when the first rifting occurred between North America and Europe. As the primordial Atlantic ocean widened, the plate carrying North America began to move towards the northwest. The Pacific plate resisted, but because it is much thinner than that of North America’s, it broke. This convergence had two effects. One was to force the oceanic crust to dive down or subduct beneath North America and the other was to compress the western margin of North America causing the continental edge to buckle.
As the Pacific plate continued to subduct, volcanic islands and other geologic passengers were scraped off and welded to the continental margin in a process called accretion. Approximately 175 million years ago, two parallel island chains collided with western North America.
Over 50 million years this collision peeled the islands from the oceanic plate pushing them up the sloping edge of the continent. As the collision between North America and the Pacific plate continued, both the accreted lands and the edge of the continent become folded and faulted creating a mountain range possibly as high as the Himalayas, the western Rockies. Between this new stripe of mountainous land and the interior of North America lay the remains of the shallow coastal sea which covered most of what is now Alberta and the Peace Region. Sediment poured into this inland sea from both the new mountains to the west and the old weathered rock of the Canadian Shield to the east.
As the layers of rock flexed under the pressure they broke. Slabs of crust were pushed up and over their neighbours increasing the weight on the crust below, bending it down, creating a water-filled trench just to the east of the mountain front. This “foredeep” collected the sediment from the rising but rapidly eroding mountains to the west. The convergence of the Pacific and North American plates did not proceed smoothly, however. Periods of active mountain building alternated with lulls. Each time mountain building resumed, additional rock became involved and the mountain front moved further east, much like the progression of ripples in a carpet pushed along one edge.
During the last 80 million years of the Mesozoic era global temperatures rose, ice melted, flowed to the sea and ocean levels rose more than 200 m above current levels. Vast areas of land were flooded, creating large inland seas which reduced the continents to collections of large islands.
From the Arctic to the Gulf of Mexico a shallow sea separated the young mountainous terrain to the west from the old eroded Canadian Shield to the east.
Warm temperatures and large areas of exposed waters resulted in lush tropical environments. Heavy rains fell on lofty plateaux and the steep rivers rapidly eroded the uplifted rocks. All along the western edge of this inland sea, rivers deposited their loads of sand and silt, creating vast deltas where a diverse community of plants and animals lived and died. The conditions were ideal for the accumulation and burial of dead plant matter and eventual conversion of that organic mass into the coal deposits of the Peace Region.
The Mesozoic era profoundly changed both the geology and the biology of western Canada. In the Paleozoic era a group of fishes developed primitive lungs, allowing excursions on to dry land. These creatures evolved into amphibians who thrived on dry land but returned to water to reproduce. Evolving from amphibians, the reptiles were the first vertebrates who could live on land full-time. Their eggs had developed shells and membranes which protected and prevented them from drying. While the great dying at the end of the Paleozoic removed many species it spared some, including the reptiles.
At the beginning of the Mesozoic many ecological niches were left vacant. The plants and animals, which survived from the Paleozoic, were now offered a cornucopia of habitats in which to live. As a consequence, new species evolved rapidly. While reptiles thrived as a distinct group, they diversified greatly with some returning to the sea, some developing the gracile fingers and stretched thin skins necessary to fly while others remained on dry land. Remarkably, some of them evolved through stages into dinosaurs and more importantly for us, into the first mammals. Life continued to flourish in the oceans of the Earth. Swimming reptiles had joined the fishes and the variety of swimming, crawling and burrowing invertebrates had increased. Tentacled anemones constructed huge reefs on the ocean floor while ammonites, relatives of the squid and octopus, hunted in the waters above.
The Mesozoic era ended with a bang, when a 10 km wide chunk of space debris struck the Earth in the Caribbean ocean, creating a crater almost 200 km across. The immediate effects of shock waves, heat, tsunamis and the protracted effects of globe encircling dust clouds which blocked sunlight, prevented photosynthesis and drastically reduced temperatures, ensured the extinction of more than half the species on Earth. While the dinosaurs were already in decline, this event ended their reign as the dominant land animals of the day although their descendants, the birds, survived. Mammals, which first appeared in the Mesozoic era, also survived. Many of the small, shrew-like mammals lived as burrowers, stocking larders with seeds and nuts, unwittingly preparing themselves for the hardships ahead. The large carnivores, which relied on the immediate availability of prey, had no reserves to carry them through the long darkness and disappeared, Jurassic Park notwithstanding.
While the impact ending the Mesozoic was catastrophic for the biosphere it had little effect on the geologic processes that continued to shape the Earth’s surface. The last phase of mountain building, which began about 85 million years ago, busily folded and faulted the thick sequence of sedimentary rock into the front ranges and foothills of the Rocky Mountains, visible in the Pine Pass. The last of the many oceans to cover the Peace Region receded about 75 million years ago, effectively ending the accumulation of new sediment. And, approximately 45 million years ago, mountain building halted when the collision between the North American and Pacific plates ceased. Western North America now consisted of a series of fragments or terranes welded to the ancient core with the intervening crust compressed and thickened. If humans existed in the Peace Region, they would have gazed in awe at the towering, snow covered plateau to the west, similar to the present Tibetan plateau.
The present geologic era, the Cenozoic, heralded the rise of mammals as the dominant animals of the Earth. The Earth had become warm and the Peace Region enjoyed a tropical climate. Lush swampy forests harbored a broad variety of species, including many small tree dwelling mammals who seemed to thrive on fruit and seeds, indicated by the tooth structures of fossil species. Around 50 million years ago modern groups of mammals appeared. True primates, hoofed animals and rodents joined and, in many cases, replaced their older relatives. Eohippus, the dawn horse, appeared in North America, scuttling around in the underbrush. Some mammals returned to the sea. Brontotheres, resembling rhinoceroses, and giant ground sloths munched their veggies, enduring the frequent Earthquakes caused by the still rising Rocky Mountains.
In the middle of the Cenozoic era temperatures began to decline. The Peace Region became drier and a mixed coniferous and deciduous forest replaced the jungle. Grasses covered open areas providing more palatable nutrition than leaves and twigs. Animals responded by evolving broad molars and the long legs of runners in order to thrive in the new grasslands. While many species of plants and animals from that time have become extinct, the biological and geological appearance of the Peace Region would have been quite similar to their appearance today. The Rocky Mountains would have been much higher and impressive but the foothills and plains were in modern form. A walk through the forests and grasslands, with their animal populations, would be as familiar then as now.
The last stage in the geological evolution of the Peace Region and Western Canada began 1.9 million years ago. Natural cycles in the shape of the Earth’s orbit and the inclination of the Earth’s axis conspired to plunge the Earth into a deep freeze. Snow, which usually melted in summer, remained and turned to ice whose depth increased with each new snowfall. Eventually the pressure forced the ice to flow. From centres in the arctic and in the western mountains glaciers flowed out across Canada, reaching depths of 4 kilometers in the Peace Region. The tremendous weight of ice made the bedrock pliable, plucking pieces loose and grinding rock into flour. The ice carried everything along and, at the edges of the glaciers, this sediment melted out and assumed various forms. Some of it simply blanketed the ground, some piled up as moraines and some was shaped into long hills called drumlins, visible in many areas of the Peace. This vast excavation carved deep, U-shaped valleys, rounded some hills and shaped others into sharp peaks, dissecting the vast plateau of western North America into the spectacular mountains which inspire us today.
Ice finally left the Peace Region 12 thousand years ago. It is the present. Long ago magma became rock over which countless seas have washed, mountains grew to grandeur then faded as erosion triumphed, strange plants and animals appeared, thrived and then vanished while others took their place. And somewhere in the forest of the Peace Region an old whitetail deer struggles through the deep snow, weakened by age and the scars which it brings. It haltingly scratches through the cold crust, searching for some morsel of food, warily scanning the forest depths. And there, hidden in the shadows, a pack of wolves, simply intent on its own survival, eyes its prey. With noiseless signals, the pack members find their positions and attack. The deer’s valiant defense quickly fades and, with its energy spent, it seemingly accepts its fate and collapses to the ground. Maybe some bones will be left, uneaten, to be entombed in mud and sand deposited by a flooding river. Possibly its bones will become fossilized and, eons from now, some paleontologist, a member of the species which replaces us, will stumble upon them. We can only imagine the scene as that creature gazes with wonder and speculates on our place and lives.