FIFTY KILOMETRES BELOW HIS FEET on that morning in late June 1988, the descending shock waves hit something big and very hard: a submerged island maybe, a slab of planetary crust, or perhaps a portion of a continent that no one has seen and no one ever will see. The shock waves ricochetted upward through the rock, carrying with them a message from the lost worlds of the Pacific. They had emanated from powerful vibrating pads on four bizarre-looking, 25-tonne trucks parked bumper-to-bumper along Duffy Lake Road, a narrow aperture through British Columbia's forested Coast Mountains, 150 kilometres north of Vancouver. The buried rock is one section of a massive piece of the ever- moving lithosphere - the rigid outer shell of the planet - that has disappeared under North America. It is slowly heading eastward, carried down by the forces that cause sea floors to spread and continents to drift.
The man standing beside the rumbling trucks is Fred Cook, a University of Calgary geoscientist, one of a team of some 600 Canadian scientists midway through a 20-year, $l00-million project called Lithoprobe. Unlike cartographers of centuries past who charted the planet's surface, the team's goal is to map a cross section of the North American continent, a 50-kilometre-deep vertical slice from southern British Columbia to the northern tip of Labrador. Their aim is to fathom how the continent formed during its four-billion-year history and what is happening down there today. Lithoprobe has already discovered remnants of submerged mountains under parts of Ontario and Quebec that once stood higher than the Himalayas; a buried rift valley far beneath Lake Superior that was once 30 kilometres deep; and, of more current concern, the best details ever of the deep ore bodies near Sudbury, Ont., and the subduction zone off Vancouver Island where a major earthquake is overdue.
Until about 30 years ago, the inner workings of the planet were largely unknown. Drill holes and mines went down just a few kilometres and deep seismic soundings were relatively crude. The planet's surface was a mask hiding the malleable subsurface far beneath. Among geologists, little was certain about how Earth evolved as a planet, how its oceans and continents formed, how mountains came to be, and what lay beneath the rocky veneer.
Scientists knew only the basics: the Earth's core, comprising a little more than half its 6,370-kilometre radius, is principally iron, which pressure keeps solid despite temperatures of 4,000┬░C. The surrounding mantle is a 2,900-kilometre-thick zone of iron and magnesium silicate rock. The lithosphere, a 300-kilometre-thick shell, floats on a partially molten layer of the upper mantel. The upper eight to 65 kilometres of this is the crust. The lithosphere is seemingly solid -- but curiously unstable and mobile -- and fractured into 12 major plates and many smaller chunks. Some of the plates contain continents.
Until recently, geologists didn't understand the mechanisms driving these plates. The key that unlocked the mystery was the realization that the entire planet is in flux, its surface shell a chaotic aggregation of ocean basins and landmasses, drifting up to 10 centimetres a year, the same rate fingernails grow. Propelled by the slowly churning convection currents of the mantle rocks below, these plates collide, crack, bend and even disappear into the Earth's depths, bearing their history downward like old memories into the subconscious. In scientific jargon this is plate tectonics. The task of Lithoprobe, like that of a psychotherapist, is to reveal the features of that concealed world.
ON ANOTHER DAY IN LATE JUNE, 6,000 kilometres to the east of Cook and his seismic trucks, Richard Wardle, senior geologist with the Newfoundland Geological Surveys Branch, stepped out of his tent and surveyed the grey sky of northern Labrador. "There are two kinds of weather there," he said of his Iselin Harbour base camp, home that day to 20 field geologists. "There's the horrible and the really horrible."
Under icy fog or gale-force winds, Wardle and his crew sought to discover -- in daily traverses of the bleak, I,700-metre Torngat Mountains -- the nature of the area's metamorphic rocks: their geochemistry, age and history. This work would be stitched together with the efforts of the research vessel Vetter, simultaneously cruising the Labrador Sea just offshore. Firing compressed-air explosions every 20 seconds near the ocean surface, the shipboard Lithoprobe crew recorded through sensitive hydrophones the seismic messages bouncing off layers in the lithosphere far beneath the sea floor.
What Wardle found in Labrador, what Cook found in British Columbia, what dozens of other Canadian scientists -- including Lithoprobe director Ron Clowes -- are finding is nothing less than the history of the North American continent right back to its beginnings, shortly after the Earth itself formed 4.5 billion years ago. This sort of work has never been done before on any continent.
"One of our purposes was to define the basic structure of the continent," says Clowes, a professor of geophysics at the University of British Columbia. "From geological mapping, we already had two dimensions: the width and breadth -- the surface. What was missing was the third dimension: depth. Now, with our new seismic and computing technology, we can get an accurate -- but fuzzy -- picture of what's below. This gives us the present structure -- like a snapshot of the continent now. What we want next is the fourth dimension: time. What processes have gone on since the continent formed almost four billion years ago? The oldest rocks on Earth are from the Northwest Territories. Some of the youngest rocks are forming today off Vancouver Island at the western edge of the Juan de Fuca Plate. This makes Canada a marvelous laboratory for a project like Lithoprobe."
Clowes' office shelves and tables are jammed with testimony to a decade of shepherding dozens of grant proposals, scores of graduate students, 28 Canadian universities, 10 multi-year field studies, reams of computer data, and 700 published reports through various government agencies and corporations involved with Lithoprobe. Because it is a multi-disciplinary project drawing from every earth science, because of its strong base in the corporate world where mining and oil companies see its benefits, because it is one of the largest scientific endeavours in Canadian history, it is, to say the least, a logistical challenge.
Lithoprobe began in 1984 as a small pilot study, headed by Clowes, of the crystal movements beneath Vancouver Island and its adjacent sea bottom. Funded initially by two federal agencies, the Natural Sciences and Engineering Research Council and the Geological Survey of Canada, it slowly grew as Clowes and his team of scientists expanded the range of their studies to virtually every province and territory -- from the mineral-rich Kapuskasing region of central Ontario to Newfoundland, where evidence exists of an ancient super-continent that once joined North America, Europe and Africa. By 1987, the federal commitment to Lithoprobe assured funding totalling $76 million until 2003. Along the way, mining and petroleum companies recognized they could use the fundamental research the project was producing, and have contributed $14 million in seismic data, services, equipment and cash. Various provincial research bodies and Canadian universities have kicked in another $8 million.
OVER THE PAST DECADE Clowes and his teams have compiled a list of significant Canadian geological mysteries in 10 study areas. Why is it, for example, that rocks of apparent African origin are found in eastern Newfoundland? What explains the diamond-bearing zones of the Northwest Territories? How did rocks from 40 kilometres beneath the surface get shoved upward in Ontario 1.25 billion years ago to create the highest mountain range in history? What exactly are the modern earthquake dangers in British Columbia?
To answer the last question, Clowes, Cook and colleagues set up the first and westernmost Lithoprobe survey, called the Southern Cordillera Transect (transect means cross-cut), extending through southern British Columbia and crossing the active earthquake region. They began their five-year study using the main -- but by no means only -- Lithoprobe procedure, called seismic reflection. With four Calgary-based seismic trucks, the crew set out from Bamfield, on Vancouver Island's west coast, on a slug's-paced climb eastward across the island's mountainous spine. The trucks stopped every 100 metres along the logging roads that dissect the island while thousands of linked, super-sensitive geophones were stuck into the ground every few metres over a distance of almost 10 kilometres. Working in tandem, the trucks used hydraulic vibrator pads which, when lowered, raised their wheels off the ground. At Clowes' command from within the control truck, the pads began pounding the ground in synchronized, 14-second, jackhammer-like bursts -- which explains why some call the trucks "dancing elephants."
The vibrations, barely audible, travelled dozens of kilometres downward through the Earth. There they hit various planes of submerged strata and rebounded upward toward the geophones, which collected the waves and relayed the impulses to the control truck. Computers processed the masses of data, then generated a cross-section map of the Earth below, something that looks -- to the untrained eye -- like grey-black cirrus clouds on white graph paper. To Clowes, however, these images provided some of the first pictures ever of the workings of plate tectonics.
When all the computer analysis was done, he saw clear images of the bottom sediments of the Pacific Ocean and, 15 kilometres below that, a massive piece of oceanic crust called the Juan de Fuca Plate thrusting under North America. This movement, which has occurred for 150 million years, is the source of the major earthquake danger in British Columbia.
On the seismic charts in his office, Clowes produces evidence of what's happening and what it means. It should make British Columbians quake. The print-out looks like the fuzzy ultrasound image of a gargantuan, four-metre-long fetus. But on closer inspection the dots resolve themselves into patterns: sloping planes, downward curving crust, buried strata. Tracing these lines with his fingertips, he explains it appears that the descending Juan de Fuca Plate has become lodged -- locked -- beneath the North American Plate.
"Every other mega-thrust (or sliding under) fault zone has had a mega-thrust earthquake," he says ominously. "Alaska in 1964. Mexico a few years ago. The last big one here though was over 300 years ago. From what we know, there's a high probability of a mega-thrust earthquake here. Probably off the west coast of Vancouver Island. A 9-plus. Or under Vancouver Island. Maybe 8-plus." He goes on to say that its destructive power could easily mirror that of the recent quake in Kobe, Japan, and its timing is unpredictable.
ACROSS THE CONTINENT, it was not earthquakes, but polar bears and wolves Wardle was thinking about. The bears would, occasionally, nose through the Labrador field camp in broad daylight while the frigid nights were alive with howling. Wardle faced a very different tectonic puzzle than Clowes. In a region of ancient rocks and crystal collisions, some dating back over 3.8 billion years, he regularly found himself asking what forces had been reworking the continent, plowing up mountain chains, obliterating entire archipelagos, splitting landmasses and forming oceans only later to destroy them? This happened again and again, as continents collided several times where Labrador now sits. The evidence is all there, etched in stone.
Each morning, Wardle's crews would climb into a helicopter loaded with aerial photos, maps, compasses and a day's supply of gorp. In that blasted, treeless subarctic region, mountainous and barely explored, there was no possibility of doing seismic reflection. There are no roads. Wardle's project -- called the Eastern Canadian Shield Onshore-Offshore Transect -- required lots of good, old-fashioned footwork.
In day long traverses of I0 to 20 kilometres the Lithoprobe geologists did what geologists have done for 200 years: they banged rocks, took rock samples, and made geological maps. Back in the camp, the samples and data became part of patterns, then theories. Back in the laboratory, the geo-chemistry told where within the lithosphere the rocks formed. The amount of natural radioactive decay in uranium and potassium deposits told their age. And the alignment of magnetic minerals revealed clues about the order of events. Gradually, theories gave way to understanding.
"What we've learned," Wardle says now from his St. John's office, "is what actually happens when one continent collides with another and all the bits and pieces get squeezed together. We've found rocks that originally formed at the surface and have been plunged down 30 to 35 kilometres into the lithosphere, almost to the base of the crust. We've seen volcanic offshore islands that got squished between two colliding continents. We've seen how Labrador and Greenland split 80 million years ago. We've seen rocks here that are the same as rocks in Scandinavia -- from the time the two continents were one. The history of the Earth is one of constant collision and separation."
OF THE 10 PLANNED LITHOPROBE transects, four are done, four are underway, and two are just beginning. So far, the most astonishing findings centre on the Great Lakes region where the world's highest mountain range and deepest valley once existed. The mountains resulted from the largest collision ever to occur on the planet -- as a northwestward-sliding continent struck the ancient core of North America more than 1.2 billion years ago. Banded metamorphic rocks along Ontario's Georgian Bay -- along with Lithoprobe findings -- provide evidence of this encounter, although little remains of these mountains on the surface today. One hundred million years after that cataclysmic collision, a gigantic scythe-shaped crack, curving northward from Kansas to southern Ontario, split the surface in a rift valley 15 times deeper than today's Grand Canyon -- and almost broke up the old supercontinent. Lithoprobe has shown that the planet's crust became so thin that molten rock from the mantle flowed upward into the valley, filling it to a depth of 20 kilometres. Another 10 kilometres of sediment later erased the valley completely, leaving on nothing more than a scar on the lithosphere.
Much of the Lithoprobe project has little immediate social or economic effect. Still, Canadian corporations have plowed $14 million into it because they can see the long-term benefits. Clowes' West Coast work has alerted civil engineers and governments to the potential of an earthquake disaster. They have sought in the transects in Newfoundland and Alberta the correlation between deep crystal rock and overlying sediments where oil reserves are found. Transects in Saskatchewan, Manitoba, Ontario, Quebec and the Maritimes have helped redefine for mineral exploration companies possible ore bodies.
In the summer of 1995, Lithoprobe rattled the continent with a massive explosion near Great Slave Lake in the Northwest Territories, not far from the site of the world's most ancient rocks -- metamorphic gneisses containing zircon crystals that are almost four billion years old. The crew detonated 25,000 kilograms of chemical explosives in 50-metre-deep drill holes, sending shock waves to the base of the lithosphere and outward to geophones as far away as Colorado. Part of this work is to probe the deepest structures of the lithosphere (and beyond even, into the asthenosphere, some 250 kilometres down). This may provide information modern diamond miners can use. In the last three years, possible diamond-bearing sites have been staked across Alberta, Saskatchewan and the Northwest Territories, where prospectors have discovered evidence of conditions similar to the diamond fields of South Africa.
Says Hugh Morris, a longtime mining executive and chairman of the board for Lithoprobe, "Until pretty recently, we could only look down a kilometre or so. The rest was guesswork, deductive guesswork, but full of uncertainties. Now we can look down at the whole continent. From top to bottom. It gives us a far superior understanding of the Earth and that will drive the explorers." He then names three sites -- near Sudbury, Ont., in Matagami, Que., and in Newfoundland -- where Lithoprobe has already aided the search for deep ore resources.
ULTIMATELY, THOUGH, IT IS NOT the commercial benefits that drive Clowes and his colleagues. It is, instead, the pursuit of fundamental science. Lithoprobe's breakthroughs have been compared to the effect on astronomy when the telescope was invented four centuries ago. Until that time, the universe was full of mysteries. And until Lithoprobe, so was the Earth.
Says Ray Price, professor of geological sciences at Queen's University and one of the country's leading geoscientists, "On Mars, the moon, Venus, the evidence of what happened at their beginnings is still there: the accretion of extra-terrestrial scars, the craters. The Earth is different; it's an active planet, its history pretty much destroyed by continents drifting, mountain-building, erosion. Lithoprobe now bridges the gap between geology and planetology. We get the whole history of the Earth, back to when the planet was forming, back to the beginning of time."
Some of the Lithoprobe transects, including those on the coasts, focused on the upper part of the lithosphere. In the last two years, the transects in the interior of the continent have been delving into the deepest parts of the continent -- right down to the hot and slowly churning mantle. The recent explosion near Great Slave Lake, in fact, was the biggest salvo so far in this pioneering effort.
When it is all over and all the dancing elephants and detonations and helicopters and rock-banging and computer analysis are done with, Canada will stand in the forefront of global geology, having gone -- to use a resonant phrase --where no one has gone before.
