Granite. Ordinary granite. Its heft weighed in my hands. I rotated the muddy chunk with numb fingers to better examine the clear quartz within. "Intrusive igneous rock", I thought. No magnifying glass was required to make out the hexagonal prisms of quartz's crystals. "Slow-cooling too", I reasoned, for otherwise the crystals would be invisibly tiny to my unaided eye.
In geology, I am a novice, a mere child for whom the slightest glint or sparkle suffices to delight. In my specimen, quartz seems to float in an amorphous matrix of feldspars -- salmon-pink colored orthoclase and white plagioclase -- with black rectangular chunks of biotite, or maybe hornblende, mixed in [1]. With a steel rock hammer, I had just chipped it out of a road cut. That road is the "Old 66", as locals call it, or "NM 333", as the highway department designates it.
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| Sandia Granite, formed 1.4 billion years ago, from a road cut on NM 333 between Albuquerque and Tijeras, NM. |
Just east of Albuquerque, Old 66 traverses the geologically-rich Tijeras Canyon. Stretching, rifting, and faulting of the earth's crust in these parts 10 to 20 million years ago uplifted that slow-cooling, subterranean granite, repositioning it overhead as the Sandia Mountains, and opening this Canyon. Here history, both geological and cultural, lurks.
"Along this very road", I thought, imagining Steinbeck's Joad family escaping the Oklahoma Dust Bowl in their overloaded, westbound jalopy. "Salt of the earth, as much as this rock in my hand." Conflating the movie version with the novel, I saw in my mind's eye a young Henry Fonda at the wheel, hungry, lean, and desperate. Old 66 symbolizes America and our restless drive, whether to escape, like the Joads, or instead to celebrate. "Get your kicks on Route 66." I hear that now, in Nat King Cole's cool baritone. And here I was literally walking the very road, rock hammer in hand, collecting specimens, and, yes, getting my kicks.
Wind blew wet and cold for this bleak October day of 2019. Chilling it further was the damp wake of occasional, fast-moving traffic as we worked from the road's narrow shoulder. "Grab your specimens and go", I reminded myself. "Keep focused, keep moving, stay warm, this is only the first of several scheduled stops. Others in the group are already in the car waiting for you." For Professor Carol A. Hill's class "Geology of the Sandia Mountains and the Rio Grande Rift", this was the optional field trip for the hardcore enthusiasts.
"One point four billion years old?", I asked aloud, knowing the number from books [2], as well as from her lectures, yet not quite ready to accept it. "Yes", Professor Hill replied. It is a matter of fact. Granite. Mundane granite, quite literally mundane, removed from the earth with a whack of the hammer. This chunk in my hand is enormously, unimaginably old. That much I understood.
America, our America, in contrast, repels the cling of history, or so it seems. Everything is always changing, wrecked or improved, opinions differ, in any case superseding what came before. Nearby Interstate 40, for instance, has made Old 66 a relic of a former, forgotten era. Long gone are the Art Deco motor lodges and sleek filling stations servicing streamlined cars. And these days, who still remembers Nat King Cole? As our culture forever morphs, these rocks and this earth remain, mute witnesses to it all, biding their time.
I have long worked with unimaginable numbers. Is there anything larger than Avogadro's constant of chemistry, or anything smaller than Planck's constant of physics? Just key them into your calculator using scientific notation. Easy, right? But 1.4 billion years is more than a number. It is also history, geological history, and as history it is a human creation. I ought to be able to feel it in order to fully know it.
One way to comprehend is to temporarily put aside the units -- years -- and only consider the magnitude. America has many billionaires. Can I comprehend their wealth? (Not really. I am satisfied simply to pay off my credit card balance each month.) Instead, as we are concerned with time, what about 1.4 billion seconds? How long might that be? About 44 years, according to my 33 year old HP-15c calculator. That's human middle age. Already, I've lived more than 1.4 billion seconds. That duration I know viscerally. I feel it as aches in my joints and muscles after several hours of hiking.
The relevant quantity, however, is 1.4 billion years. Because there are about 32 million seconds in a year, the age of my granite chunk is equivalent to 32 million middle-aged human lives, stacked end to end. No, I can't comprehend that either.
Another technique is to ignore the number's size and instead locate it in the context of what is already understood. In 2003, I visited the ancient bristlecone pines high in the White Mountains bordering California and Nevada. Immediately, as I walked among these scraggly Methuselahs of trees, I comprehended -- I felt in my marrow -- their 3000 year old age. Younger than the Trojan War I reasoned [3], yet also older than Homer's singing about the War in his epics, the Odyssey and the Iliad. I could understand because the Odyssey I have known and loved since childhood. Some stories of our cultural history evidently endure unchanged.
Earth's history has analogous mileposts. Life emerged on earth between 3.8 and 3.5 billion years ago and, much later, by 0.54 billion years ago life had evolved hard shells that preserved well as fossils. Somewhere within this three billion year span between life and fossils my chunk of granite cooled and solidified from magma. But, unlike the bristlecone pines, I still have no intuition or feeling for the age of the rock in my hand. The distance between the mileposts is just too great.
I am trained as an experimental scientist. I approach geology in that way. On another field trip, to a remote location near Socorro, NM in December 2019, I found a hefty chunk of glassy, translucent crystal [4]. It formed in sheet-like layers, almost like ice. Could it also be quartz? I tried, and succeeded, at scratching it with a knife. No, it definitely was not quartz. Then I watched and listened for what a drop of hydrochloric acid would do. I neither saw nor heard fizzing, so what I had was likely not calcite either. Perhaps unwisely, I licked it. Not salty, so not halite. Using established tests and guide books, using simple instruments like a knife and acid, using my five senses, and using my fallible reasoning, I tentatively conclude that what I found was selenite (crystalline calcium sulfate).
Making 1.4 billion years troublesome to me is its unapproachable abstraction. I can't taste it or try to scratch it. I cannot relate that age to my favorite stories, whether by Steinbeck or by Homer, much less to the voice of Mr. Cole. Sandia granite is found in America but seems not to be of America. I can hold a chunk of it, but I can't fully understand it, not its age. Here, my understanding hits its limits.
Footnotes
1. Sandia "granite" is, more precisely, the granite subtype called granodiorite.
2. For the geology and rock ages, see Jayne Aubele et al., "Geology of the Sandia Mountains", chapter 5 of Field Guide to the Sandia Mountains (edited by Robert Julyan and Mary Stuever), University of New Mexico Press, 2005. For background, Halka Chronic, Roadside Geology of New Mexico, Mountain Press Publishing Company, 1987, pp. xii-xiii, 27-31, 169-173, is helpful.
3. As I have understood it, the Trojan War was fought between 1200 and 1150 BCE. Homer, if he existed, travelled the Aegean in roughly 750 BCE and, over the course of several long nights, sang the epics to enthralled audiences.
4. This field trip is recounted in an earlier blog post, Land Beneath My Feet.
Posted: 2019-01-08. Updated: 2019-01-08.