BACKGROUND - Canadian Rockies: Including Banff and Jasper National Parks - page 495

GEOLOGY
The Rocky Mountains began rising 75 million years ago, making them relatively young
compared to the world's major mountain ranges. But to fully appreciate the geology of the
Rockies, you must look back many hundreds of millions of years, to the Precambrian era.
At this time, about 700 million years ago, the Pacific Ocean covered most of the western
provinces and states. The ocean advanced, then receded, several times over the next half
billion years. Each time the ocean flooded eastward it deposited layers of silt and sand on
its bed—layers that built up with each successive inundation. Starting approximately 550
million years ago, the oceans began to come alive with marine invertebrates and the first
crustaceans. As these creatures died and sank to the ocean floor, they added to the layers of
sediment. Over time, the ever-increasing sediment load compressed the underlying layers
into sandstone, shale, and quartzite.
Birth of the Rockies
Some 200 million years ago, the stability of the ocean floor began wavering along the
West Coast of North America, culminating 75 million years ago as two plates of the earth's
crust collided. According to plate tectonics theory, the earth's crust is broken into sever-