Through many posts we have talked about the Great Unconformity (yes, you must capitalize it) and how it occurs worldwide in different rock sections. Why? Scientists believe that at several times in Earth’s history the planet was buried in a blanket of ice. Oceans were nearly frozen. This is what scientists call Snowball Earth, or sometimes Slushball Earth.
The last occurred sometime before 650 million years ago, during the aptly named Cryogenian period. In 200 million years, uplift and the giant erosive conveyor belts of ice eroded continents down to the roots of the ancient mountains and left the land at sea level. Think the Canadian Shield. This scraped bare land is the base of the Great Unconformity. As the glaciers melted, sea level rose and covered the land and deposition of sedimentary layers began. Variations of this happened worldwide. We can focus on the North American continent which looked much different at that time. Forget anything west of Idaho or so. It wasn’t there yet.
Wyoming Geologist Myron Cook does a much better job than I could of explaining Snowball Earth, the Great Unconformity, and why different gaps, between hundreds of millions to billions of years of time, exist across what was North America at the time in his great video published only 11 days ago. Throw in a master-class in Deep Time, and you have it all put together as only a master story teller can. And there are lots of rocks, yay! Watch this wonderful video. Yes, it’s long, but you’ll absolutely hate yourself if you don’t get to see the Mineral Fork Tillite and how the story ends. Trust me.
Follow it up with further findings on Snowball earth using thermochronology by Kalin T. McDannell, et. al. including our own @brenhinkeller as they work to help determine if glaciation or the recent hypotheses of tectonic influence had more impact on denudation of the continent. Spoiler alert: read the title of this post again.
