“The wonders of the Grand Canyon cannot be adequately represented in symbols of speech, nor by speech itself.” — John Wesley Powell, geologist

“I believe in science and evolution. I’ve been to the Grand Canyon.” — Bill Walton 

“I believe in evolution. But I also believe, when I hike the Grand Canyon and see it at sunset, that the hand of God is there also.” — John McCain 

By DR. CAMERON BARROWS

Standing on the rim of the Grand Canyon in northern Arizona one might begin to grasp the immensity of time that has passed and the forces that created the ground on which you stand. Before you are exposed layer after layer of sandstones and limestones. The upper layer, the Kaibab Limestone, was deposited from a shallow ocean some 270 million years ago. Below that are the Toroweap and Coconino sandstones, essentially “fossilized” coastal sand dunes. You can still see angles of the dune faces blowing in the wind 275-280 million years ago. On some of those sandstone blocks you can find imprinted lizard and scorpion tracks, doing exactly what the scorpions and lizards do today on what remains of the Coachella Valley sand dunes. Lower down the canyon wall, and so older (340 million years ago), the Redwall Limestone layer includes fossil crinoids, bivalves, and snails. Follow rock layer after layer until you reach the canyon bottom, reaching the Vishnu basement rocks, igneous granites and gneisses that have been aged to over 1.8 billion years, some of the oldest exposed rocks on Earth. There you can touch the early crust, forming not long after the molten Earth began to cool.

However, there are some missing rock layers in this sequence. John Wesley Powell, the first non-indigenous person to travel down the Grand Canyon, noticed these gaps, referring to the one immediately above the Vishnu basement rocks as the “Great Unconformity.” This gap represents about 1.2 billion years of the Earth’s history, or 25-30% of the time the Earth has existed. Gone. As geologists searched around the Earth, they found this same gap everywhere these ancient rocks were exposed, creating one of the greatest unsolved geological mysteries of modern times.

That is until now. Geologists recently found rocks of the age to fill this gap on one of the Shetland Islands in northern Scotland named Garvellachs. Garvellachs somehow escaped unscathed. It may be the only place on Earth to have a detailed record of how the Earth entered one of the most catastrophic periods in its history – as well as what happened when the first animal life emerged. To solve this mystery first we need to know that back then Scotland was in a completely different place because the continents moved over time. It was south of the Earth’s equator and had a tropical climate. Geologists had developed a hypothesis to explain this geologic gap that during this missing period the Earth became engulfed in ice. It became known as the “snowball Earth” hypothesis. The idea was that at the time glaciers covered almost all the Earth’s land masses. Over time as the glacial ice moved across those rocks, it pulverized and ground down the rock layers, destroying the geologic history the rocks represented. The snowball Earth hypothesis posited that around 700-800 million years ago, as during the Pleistocene Epoch’s ice ages, the Earth’s orbit and tilt shifted away from the sun, causing polar ice caps to grow and move across the land masses. Except this time there were no extensive forests pumping out carbon dioxide, so a weaker atmospheric blanket trapping heat, and the ice grew even more and created a runaway cooling climate; the ice reflected away the sun’s heat and our planet cooled even further and was nearly engulfed in ice. Only near the equator where Garvellachs was then located was there still open water.

The rocks on Garvellachs survived but show tell-tale linear gouges characteristic of glacial erosion, probably from icebergs passing by the island. The Earth’s orbit likely shifted back closer to the sun, allowing an escape from a permanent “snowball Earth.” There also probably was increased volcanic activity, spewing lava and black ash across the glaciers, reversing the white snow’s heat reflectance, called its albedo, and becoming a dark heat absorber. The ice melted. During this “snowball Earth” it was also a critical period when unicellular and multicellular life began to evolve. As today, there were deep ocean thermal vents where life could proliferate. And there were the equatorial regions, where Garvellachs once was, where open water, albeit very cold water, still existed. Life, as it was survived the “snowball Earth” and with a warming planet, thrived. Then there were trilobites and terrestrial plants and a diversity of other life forms. That history, leading to life today, is well documented in the rocks of the Grand Canyon and elsewhere.

Nullius in verba – Go outside, tip your hat to a chuckwalla (and a cactus), and think like a mountain