As national parks go, Yoho is more compact than most. Driving the Trans-Canada, it feels you've already left it behind before you finish reading the "Welcome" sign. Yet Yoho's jewels are among the most precious in all the treasury of Canada's mountain parks. Just ask Charles Doolittle Walcott, the American geologist who discovered the Burgess Shale in 1909.
Perhaps the world's single most important fossil deposit, the 505-million-year-old Burgess documents the so-called "Cambrian Explosion"—the period when numerous new body forms emerged among early complex animals and rapidly diversified ("explosion" is a relative term peculiar to studies of deep-time—the interval actually represents tens of millions of years). Lionized in literature, film, and even a symphony, the Burgess holds pole position in a series of global outcrops that chronicle this critical period through exceptional fossilization of small, generally soft-bodied animals. With delicate structures like eyes, organs, nerves, gills, eggs and even stomach contents preserved with often stunning clarity, Burgess fossils have potential to solve biological puzzles as central as the evolution of predation, parental care, sight, and the perception of colour. Though the mechanism of their exquisite preservation has remained enigmatic until recently, the fossils' significance to both evolutionary theory and our understanding of current life on this planet is unmatched in the annals of science. Recently, the Burgess Shale again piqued popular consciousness through new discoveries and research on four different exposures within Yoho and Kootenay National Parks, fortuitously protected under the umbrella of the UNESCO Canadian Rocky Mountain Parks World Heritage Site.
All this is on my mind as I begin the infamous 21-kilometre roundtrip to the "Walcott Quarry," where the Smithsonian Institute scientist and his family excavated fossils for some 20 summers. One of three different Burgess site hikes open to the public (when accompanied by guides from either Parks Canada or the Burgess Geoscience Foundation), I'm privileged on this occasion to join a group of researchers led by Jean-Bernard Caron, the Royal Ontario Museum (ROM) scientist whose work here has sparked nothing short of a paleo-revolution. Caron curates the ROM's Burgess collection—some 200,000 specimens of 200-plus species—held in trust for Parks under a collaborative agreement.
Spry and bespectacled, Caron leads the way, eternally energized by the prospect of discovery despite making this hike a hundred times since 1998, the year he first volunteered on a ROM expedition. Growing up in France, Caron indulged his interest in fossils on summer digs across Europe, but a fascination with the Cambrian Period drew him to Canada, where he completed a PhD on Burgess palaeoecology through the University of Toronto. Following him is Bob Gaines, a California geology professor whose parents gifted him a trilobite fossil at age five, inculcating a thirst for the past realized in his current geochemical investigations of the Burgess. Beside me is Todd Keith, a Land Use Specialist with Parks Canada whose title belies a longstanding role as de facto Burgess Shale liaison. Parks' partnership with the ROM includes protecting Burgess sites, issuing collection permits, and collaborating on outreach. Bringing up the rear is an aerial-imaging team that will create a 3D map for an upcoming ROM Dawn of Life gallery. For the young-gun drone pilot with his own longstanding interest in fossils, a chance to visit paleontology's de facto shrine is a dream come true.
Openings in the trees become more frequent, views more expansive. Crossing under a cliff face below Wapta Mountain, we keep an eye out for falling rock, dive briefly back into forest, then emerge into a large rockslide with a spectacular overview of Emerald Lake and its eponymous lodge. The rockslide is a popular lunch spot, as a swarm of plump ground squirrels attest. The shameless crumb-hounds beg pieces of cookie, running over our boots as if these were merely rocks; they've done this for generations as documented in Walcott's own grainy photos. Departing, there's a final stretch of forest before a patch of ground-hugging, bonsai spruce forms a welcome mat to the alpine. The world before us reaches for the sky as we tread on what was once ocean floor 50 fathoms deep.
ROM scientists have been excavating at Walcott Quarry since 1975, and recently joined with Parks to launch an online Burgess exhibition as part of the Virtual Museum of Canada, an immersive journey that brings to life over a century of discovery. Though aiding its protection, such PR also makes the Burgess more vulnerable to vandalism and theft. As a result, as we reach the shale talus where Walcott first noticed impressions of strange creatures, signs warn of a restricted-access trail above on which only certified interpretive guides may lead hikers. From this point, Walcott had traced the fossils' origin uphill to an exposure he named for nearby Mount Burgess; to reach it we now turn onto the same switchbacks where, year after year, he and his horses climbed the equivalent of a 41-storey building. But anticipation erases any fatigue, and when we reach the famous dig, my spine tingles.
If you're a fan of the history of life, neither physical accomplishment nor appreciation for the surrounding beauty can surmount the emotion of comprehension that washes over you on this aerie: in the bricolage underfoot, you realize, impressions of an odd little riot of life that occupied a muddy ocean bottom some half-billion years ago trace an inexorable line to the present. Few hikes deliver that kind of food for thought.
Since the days of Walcott, discarded slabs of shale were pushed over the quarry edge to slide downhill. While Keith supervises the drone crew, Caron and I garbage-pick this substantive tip, bringing literal meaning to "leaving no stone unturned." He immediately finds several nice Marrella—a unique Burgess arthropod and the first collected by Walcott. Then—bingo!—a rare sponge. "Only five other specimens exist in the world," enthuses Caron, who well knows that one extra fossil almost always equals extra information.
While more recently split shale is grey, the older stuff has lightened with time, becoming infused with reddish plumes. Though odd, it's not unusual, explains Gaines, whose bubbling enthusiasm balances Caron's quiet intensity. He details how microbes metabolize iron into compounds that are then weathered out, oxidized, and essentially deposited as rust. Gaines's geochemical perspective had delivered a new dimension on the hike, as he pointed to various micro-phenomena along the trail, and now, while Caron and I search for leftover fossils, he birddog's the quarry for more evidence to shore up his theory that the spectacular preservation of Burgess fossils owes itself to a distinct ocean chemistry that discouraged microbial decomposition (see sidebar: Weather Report).
After a long day in the alpine, the 10-k., 800-vertical-metre downhill return is wearying, if not downright knee-knackering. But there's little respite. Like the Barkley Marathons of the eponymous 2014 documentary, once one loop is finished, another begins. Wobbly and sore—albeit well-fed and rested after a night at the town of Field's quirky Truffle Pigs Lodge—the next morning we undertake another of Parks' guided public hikes, this one to the Mount Stephen trilobite beds.
The trail begins right in Field, following a creek drainage before ascending a forested moraine. It's steep and relentless, but Caron is again in turbo mode and we steam upward. An hour later, we climb out of the forest and onto the original trilobite bed studied by Geological Survey of Canada geologist Richard McConnell who, following railroad workers' rumours of "stone bugs," made his first collection here in 1886, drawing Walcott to the area.
The bed is spectacular, both for its views cross-valley to the ridge we'd climbed yesterday, and an abundance of fossils that include trilobites galore. The ground, in fact, is impressively littered with these stone bugs—the kind of obscene abundance you imagine as a kid when you think of a place to pick fossils.
Aside from repeated burials by mudflows off of an underwater escarpment, Caron believes some kind of transport scenario must account for the abundance of these animals here. Gaines concurs to a degree, sparking more discussion of mud beds, faults, and escarpments. He sets off with Keith to look at some intriguing rocks upslope while Caron and the drone pilot make like mountain goats and set out perimeter flags for a flight. Walking the area, the mobility of thin slabs beneath my feet continuing their gravity-driven descent to the valley makes me think: 500 million years after they were entombed here, trilobites are again surfing along the ocean floor.
Despite interesting finds and photographic work accomplished for the gallery, these first days of a two-month field season are only a warm-up for Caron. After that, he and Gaines will spend a week on foot and by helicopter scouting for promising exposures to be quarried at a later date, drawing new horizons in ancient strata. Their finale will be a six-week field camp at Marble Canyon in Kootenay National Park, site of discoveries in 2014 that have turbo-charged the Burgess mystique.
On a grey day, Keith and I bushwhack through burned-out forest to the Marble site. Blackened logs streak our clothing front and back; likewise my hat—a catalogue of encounters with charred branches. We finally clear the forest and head up a steep ridge. The going is better until we hit the base of an avalanche chute and must move laterally, where things go haywire with downed snags—big ones—everywhere, such that we must clamber over three-to-four at a time. Snow hits us as we approach the ROM encampment. Set on a forested bench ringed by grizzly-repelling electric fence, Caron emerges to meet us, his wry grin suggesting we don't need to tell him how the hike went.
We pile into the spacious, domed mess tent for tea, a warm-up, and a meet-and-greet. After a week of rain, Caron laments that little has been accomplished in the quarry here—wet fossils don't show well. Nevertheless, he, Keith and I climb 15 minutes in a fusillade of ice pellets to the excavation littered with bins, generators, jackhammers and a range of tools. As if on cue, a rainbow appears to the east, arcing across snow-capped peaks to frame the camp, with Highway 93 winding beneath it like a yellow-brick road.
The Marble find was big news because it represented extraordinary new Burgess Shale fauna. Despite its proximity to Walcott's original locality (40 km as the crow flies), the mix of animals here is distinct, remarkable for its high density and diversity, some 22 per cent of the total comprising new species. (This shouldn't surprise anyone who has put on a snorkel to look around in the ocean—specific communities of critters are often very localized.) Marble also features the preservation of hitherto unreported anatomical features, such as the liver seen in a specimen of Metaspriggina—an early fish-like vertebrate often found in groups, suggesting aggregating behaviour for the purposes of feeding or breeding.
The next day, Caron uses clearing weather to rally his crew earlier than usual before sunlight hits the quarry. They set about splitting rocks previously pried from a productive layer. Some contain nothing, others life both obvious and not—phantom existences further reduced to shadows and traces, outlines and suggestions. After lunch I leave them behind to descend back to the valley and the town of Radium. I have one more stop to make in my deep-time marathon.
Next morning is my chance to hike with the non-technical masses. I join a Parks Canada-led excursion to Stanley Glacier, an excellent Burgess introduction on a relatively easy trail. Meeting at a roadside parking area with a guide and 11 others (a maximum of 12 are allowed), the trail crosses the Vermilion River on a narrow wooden bridge, then gently gains elevation on well-graded switchbacks, passing through the remains of the 1968 Vermilion Pass fire. Walking across a bench and out of a shallow, forested valley, the transition is abrupt as the trees give way to a huge, rock amphitheatre hung with what's left of the Stanley Glacier. The soaring walls of this enclave, draped with silver threads of meltwater, contain the outcrops, the fossils scattered on talus below. As the guide passes around some of the better impressions, I find the looks on faces of the tourists from France and Britain and Germany even more intriguing, in particular the children, who seem genuinely gobsmacked by these marvels. The air of revelation and reverence that descends on the group is a perfect one to wrap this multi-day enterprise.
Over a century after their discovery, the spectacular fossils of the Burgess Shale continue to reveal the deepest secrets of evolution to the scientists who study them. But if you have a few days and the legs for a hike or two, they also deliver something else—a walk into our own past along an ocean floor in the sky.
This article originally appeared in the fall 2017 issue of British Columbia Magazine
By preserving delicate structures and tissues unlikely to fossilize under normal circumstances, Burgess Shale-type deposits provide a startling record of the rapid diversification of early complex life—the so-called Cambrian Explosion. How this occurred has remained enigmatic. Bob Gaines, however, believes he has unlocked the mystery.
Gaines and an international team collected physical and chemical evidence from the Burgess Shale and six similar-aged deposits in China and North America, pegging their extraordinary preservation to severe restriction of microbial activity after burial, due to a lack of oxygen and sulfate normally respired by microbes during decomposition. Furthermore, the mechanism of this restriction appeared to be successive formation of thin carpets of calcium carbonate on the sea floor—mineral barriers that prevented exchange of seawater with fossil-bearing sediments below. With the Burgess Shale itself, formed below the geologic structure known as the Cathedral Escarpment, each critter-entombing mudflow off the scarp was followed by formation of a corresponding carbonate layer. But why, researchers wondered, were Cambrian seas characterized by high-calcium carbonate and low oxygen and sulfate levels?
Here, geochemical forensics led researchers to the Great Unconformity, a long-acknowledged global geologic phenomenon in which igneous and metamorphic basement rocks of the Precambrian are overlain by several-kilometre thick layers of Cambrian sediment. While life flowered in the oceans but had yet to occupy land, these continental rocks underwent unprecedented erosion. Gaines and company hypothesized that the accompanying high rates of chemical weathering would have profoundly impacted ocean chemistry.
As falling rain mixes with atmospheric CO2, it becomes more acidic, leaching elements from rock and transporting them in dissolved form. It's an important part of the geologic carbon cycle: during chemical weathering, atmospheric CO2 is transformed to bicarbonate (HCO3-) and delivered to the oceans, combining there with calcium (Ca2+) to produce calcium carbonate (CaCO3). Many marine organisms—both micro- and macroscopic—use this compound to produce mineralized shells and skeletons that are subsequently fossilized.
Thus, high concentrations of calcium carbonate may not only have restricted the decomposition of organic matter that led to Burgess Shale-type preservation, but helped spur the Cambrian Explosion by promoting early acquisition of the minerals used in skeletons.