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“Animals might be evolution’s icing, but bacteria are really the cake.”
—Andrew Knoll, How Did Life Begin?
October 11, 2015
No GPS, no compass. No field guide. Not even an index card with hastily scrawled directions. Just a few UTM coordinates and a useless vehicle use map.
I mention these things, not as a testament to my navigational skills, nor to my forgetfulness regarding things I should have packed, but rather as an indication of just how big the structure I’m looking for today is.
West of Laramie, WYO 130 climbs from the grassy high plains and into the Medicine Bow Mountains. Though at over 10,000 feet in elevation, the area just east of the main crest isn’t all that rugged. This is Libby Flats, a strange landscape of alpine meadows and glacial lakes and Engelmann spruce.
I get my bearing from the sun and walk north from the dirt road. Although I start out counting my paces, it doesn’t take me long to lose track—an unassuming clump of rock breaks my concentration.
It’s Nash Fork Formation meta-dolomite—I must be getting close.
Two billion years ago, this mountainous region resembled the gulf coast—shallow seas and reefs and white sands, minus the resort hotels, of course. But coral—our friendly modern-day reef builder—wouldn’t evolve for over another billion years, and so the residents of these ancient reefs were quite different than those we see today. In the modern, biogenic structures such as those in the Nash Fork Formation are found only in waters so saline the area is inhospitable to any other living thing, such as in Shark Bay, Australia.
I consult the map. My route so far in no way resembles the route recommended by the WSGS field guide. Working from memory (as I, of course, forgot the wonderfully detailed said publication), I climb up and over the ridge to the northwest, through the wind and lone groves of trees and more wind. Below me lies Prospector Lake, and from here, I can already spot the outcrop the field guide refers to as “Big Daddy,” a mass of white jutting out into the water along the opposite shore. To the south a much gentler path than my improvised one wraps around the ridge, well-worn by University of Wyoming students and other paleontological pilgrims.
Up close the outcrop looks like a giant, silicified head of cabbage, its thin layers of metamorphosed sediment produced by the activity of ancient colonies of microorganisms. The bacteria in these microbial mats were photosynthetic, and so as they converted sunlight into energy, they depleted the surrounding water of its carbon dioxide, causing calcium carbonate to precipitate. These carbonate minerals became trapped by the sticky mucilage of the bacterial colonials, and the cyanobacteria would then grow up through this sticky mess, toward the sun. Each iteration of this process created a new layer of carbonate sediment, hence the name of this biogenic structure—stromatolite—which literally means “layered rock.”
In this way, although the ancient life of the Precambrian may have been microscopic, the evidence it left behind can been seen with the naked eye. Stromatolites would often form modest, basketball-sized mounds, but “Big Daddy” here in the Medicine Bows is over fifteen feet across.
After I finish my communion with some of the first life on Earth, I take the established trail back to the road, saving any unnecessary ridge traverses for another day. A length of survey tape stretches across a small gully, which the field guide dubs the “Valley of Stromatolites.” A metal plate and sledgehammer rest in the grass alongside the tape. Lurking somewhere in these hills, a geophysicist shields his computer screen from the sun, reviewing the data from his seismic survey. By banging on the metal plate with the hammer and measuring the vibrations, he’s able to produce an image of the subsurface, probing even deeper into the landscape around us.
Because when the story is buried, sometimes an ear to the ground is enough, and sometimes you need a hammer.