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Rock, time and teenagers

Possible exfoliation jointing in Permian Esplanade Sandstone. Scouts for scale

Howard Lee FGS recently sold himself down the river with a bunch of adolescents.  It was a learning experience on both sides...


Geoscientist 21.1 February 2011


It’s probably on the “bucket list” of every geologist (even a lapsed one like me). So when the opportunity came to raft down the Colorado River through the Grand Canyon, I jumped at it. But there was a catch. I would be one of a small group of adults chaperoning teenage boy scouts. Everything has its price.

As the day of departure drew near I took it upon myself to educate the troupe a little about the incredible geological story represented there. Perhaps I should have got the hint when the Scoutmaster kept postponing my session (eventually making it a ‘filler’ on the long coach ride between Las Vegas and our lodge at Marble Canyon). I should have realised the interest gulf when, given the choice to visit Barringer Meteor Crater, or a common or garden cinder cone…they chose the cinder cone!

I couldn’t bear the thought that the Scouts would traverse such spectacular geology blindly. It would be like visiting a great art gallery and barely noticing there was paint in frames along the walls. I would not bother them with rock classification, current bedding, metamorphosis, dikes and sills, or the tectonic significance of the uplift of the Colorado Plateau. Just stick to the basics, I thought. Suffice it that they grasp an inkling of the time spanned by the Canyon rocks, or the fact that they could not have breathed the air of that far-off Earth where the oldest rocks of the canyon formed, or that the age of dinosaurs came and went in one of the very last chapters of the Canyon story.


The Great Angular Unconformity, Blacktail Canyon. Cambrian Tapeats Sandstone on Precambrian Vishnu Schist

JAW DROPPED


The Scouts had been up without sleep for some 16 hours when I was finally allowed to make my presentation. I had figured on 20 minute stops – 100 million years per minute. But with each sentence I watched eyelids grow heavy, heads loll and mouths slacken. I edited as I spoke. Out went the Columbia and Rodinia supercontinents. I kept Snowball Earth…one boy’s jaw dropped … but it was slumber rather than interest. I kept in the arrival of atmospheric oxygen by the time of the Tapeats Sandstone; but out went Ediacara fauna, and Pannotia. I’m not sure how many were awake when, five minutes later, I had arrived at the end of the Permian; but life in the audience had had a mass extinction of its own. I left out the entire Mesozoic and Cenozoic except to mention the incision of the Grand Canyon and volcanic eruptions in the last five million years.

Humbled, I resigned myself to appreciating my surroundings alone, and gave myself up to appropriate reflections. I kept quiet about the Upper Permian Kaibab Limestone on the riverbank opposite us when we loaded up the “J-rig” rafts the following day, but it wasn’t long before the guides had us on a small hike into Jackass Canyon to look at reptile tracks in Coconino Sandstone blocks that had fallen from the cliffs above. When I effused about these 275 million year-old, pre-dinosaur footprints, I’m not sure if I sparked much interest. The Scouts were here for the rapids. For me, the rapids were an inconvenience that made me put my camera away.

By evening we had reached the expansive Redwall Cavern dotted with crinoid and bryozoan fossils of the Mississippian Redwall Limestone. We camped by Nautiloid Canyon, named for the fossils in its walls. By now people were asking me to distinguish the fossils from the rock and were getting photos for themselves. Progress! We slept under the stars as the moon illuminated clouds in the gap between the canyon walls.
The next day found us in an exploratory adit for the Marble Canyon Dam. This project which would have flooded a major portion of the Grand Canyon, was started in the 1950s but was cancelled after an outcry. As we wound our way further into the inner recess of the Canyon we stopped and swam in the Little Colorado River (the main Colorado River at that point is dangerously cold to swim in, even in summer) where I searched the Cambrian Tapeats Sandstone (in vain) for fossils. There were abundant worm-like burrow trace fossils but sadly no shells. I wondered if this could be the portion of the Tapeats that predates the “Cambrian explosion”.


A dyke of Early Proterozoic Zoroaster Granite forms one wall of the Grand Canyon, near mile 122. In the background most of the major units of Grand Canyon Geology can be seen.

CONVERSION


The first sign of conversion came at mile 64 when the Great Angular Unconformity hove into view. This chronological gap between the Tapeats Sandstone and the approximately 1100 Million year-old Dox Sandstone was not to be missed, so I begged the guide to let me climb the short way up the cliff to the exposure. To my amazement, two Scouts scrambled up with me, eager to have their photo taken with 550 million years in the span of their hand. Two down, twenty to go. Happily, as soon as I started talking to them about schists, cleavage and dykes – something I clearly should have done earlier - everyone took notice.

Our remaining days in the Canyon were spent sometimes hanging on for dear life through rapids, sometimes on long lazy stretches, just gazing at the staircase of terraces rising above us. We hiked into slot-canyons, bathed in the turquoise waters of Havasu Creek, visited ancient native ruins perched on cliff tops at night. Geology was a regular topic of conversation, but even though every Scout had been taught Earth science before high school, I found a profound lack of what might be called “geo-literacy”.

One Scout thought that the Colorado River had been responsible for all the rocks in the canyon, from the Vishnu schist to the Kaibab Limestone. The concept of continents being born, mountains rising, rivers flowing, continents dying and breaking up, over and over again was just too vast for his understanding. Most had real trouble with time periods – thousands, millions and billions seemed to be interchangeable, as if they all represented a single quantity: “lots”. One of the other adult leaders commented that if the seas had come up and gone down over geological time then it shows there is no need to blame man for global warming now…
Perhaps the most disturbing conversation I had was with an adult leader. “Do you really believe in science? I mean do you think there is a religious explanation for this, or are you a full-on scientist?” I gave my usual comment that science and religion don’t occupy the same territory. Science is evidence-based and faith is not. I believe evidence.


Reptile tracks in an erratic of Coconino sandstone, Jackass Canyon, mile eight. For many people science is just another competing faith, and one they take with a pinch of salt. At least half of my son’s friends (seniors - “upper 6th” - in high school) do not believe in evolution. We live a stone’s throw from Bell Labs in a well-heeled New Jersey Suburb. This is no hick, bible-bashing backwater; this is Manhattan commuter belt, big-pharma land, Alcatel-Lucent city. All the adults and their scouting offspring are considered well-educated. Other people here have told me they simply do not believe geological timescales; so when it’s common – even the norm - for “educated” people not to understand the basic principles of our planet, I worry for the future. I worry about our Scouts who, in a decade or two, will be decision-makers in an age pressed harder by climate change and natural resource shortages.

The child is father to the man, as Wordsworth reminds us. If I can’t bridge the geo-literacy gulf in the Grand Canyon, how will they ever understand?



Further reading

  • Grand Canyon River Guide All new edition, 2009, Westwater Books, Colorado USA, ISBN-13: 987-0-916370-16-9.
  • Geology of National Parks 5th Edition 1995; Harris, Ann G; Tuttle, Esther; Tuttle, Sherwood. Kendall/Hunt Publishing Company, Dubuque, Iowa, USA. ISBN 0-7872-5275-1.
  • Geology of the Grand Canyon area: http://en.wikipedia.org/wiki/Geology_of_the_Grand_Canyon_area