On Trails (7 page)

The team split up and set to their work. Liu pulled out a small black notebook and began making notes about the fossil surface in a neat semi-cursive, complete with illustrations and GPS coordinates. Stewart got down on his knees and began using a clinometer to measure the angle of the rock surface, in order to hunt for other surfaces of a similar age nearby. Matthews, dressed in a matronly white sun hat, used what looked like a jeweler's loupe to search for evidence of zircon crystals, which could be used to radiometrically date the rock. Few of these surfaces had ever been systematically dated, in part because the zircon extraction process is extremely tedious and costly. Matthews tried to explain the process to me in terms I could understand.

“First I take the rock and I break it into tiny little bite-sized pieces, then I mill them down to powder. Then I sieve the powder. Then I mix that powder with water and put that over what's called the Roger's Table, which works on the same principle as panning for gold. I just sit there for hours with a big bucketful, spooning one tablespoonful at a time. The table jiggles, and all the dense minerals go to the very end of the table and all the light clays go to the side. Then I do that all over again. That takes a day in itself. Then there's a technique called Frantzing, where you slowly crank up the strength of a magnet and slide the minerals down tiny little chutes. Different
minerals are magnetically attracted at different strengths, so some of them get picked up. In the last stage, you use a horrible, nasty chemical called methylene iodide, which is a ‘heavy liquid,' in that it's a lot denser than water but has the same viscosity, which means that things that would normally sink in water float in it. And because zircon is particularly dense, it sinks while everything else floats up. Then I pipe that up and squirt it onto a piece of filter paper. You dry this piece of paper out, after spending three days bashing this rock to buggery, and then you put it under the microscope and you
pray
that there's something under there.”

He sighed like a man playing a game with terrible odds, but one he nevertheless enjoyed. “So I might start with a rock sample half as big as my backpack and end up with maybe forty zircon crystals so small that you can't see them.” The crystals would then be worn down with a strong acid, then measured to determine how much of the zircon's uranium had decayed into lead, which would give an indication of its age, give or take a few hundred thousand years.

A few hours later we made our way over to the area's most famous fossil bed, the blandly named D Surface, which cantilevers out high over the ocean. Before we stepped out onto the bedding plane, we removed our shoes and put on polyester booties to protect the fossils from erosion. It felt like a ritual act, as if we were stepping into a temple.

The rock was huge and flat and intricately patterned, like the floor of a mosque. After visiting a lesser bedding plane, in which I often had to squint and tilt my head to make out what was fossil and what was figment, the profusion and sharpness of the fossils on D Surface was astounding. The Pigeon Cove surface had held about fifty fossils; this one held 1,500. They were everywhere, a vast fossilized garden of fronds and blobs and spirals, some larger than a large hand.

Of course, it was not an actual garden; plants would not appear in the fossil record for another two hundred million years. For some
reason I was stuck on this point. They
looked
like plants, I kept saying. Matthews explained that this was because, this far in the past, the lines between the kingdoms grow fuzzy. We, and every organism currently living on earth, he said, are at the crown of the tree of life. Down at the base of the tree lie the very first single-celled organisms, from which everything else sprang. So the further down the trunk of the evolutionary tree you look, the more organisms resemble one another. “That's when you get into the nitty-gritty definitions of what defines, say, an animal and a fungus,” he said. “They're actually biologically really close, but they just ‘decide' to stick their cells together slightly differently. And just because one evolved to stick its cells together differently than another, one mainly just grows on dead trees, and the other has conquered the earth.”

What, then, makes a conqueror? We have sex. We eat life, not sunlight. We contain multiple cells, which in turn contain nuclei, but lack rigid walls. And, in almost every case, we grow muscles.

Muscles, I learned, are a crucial component of Liu's big question. While many kinds of organisms (even single-celled ones) can swim, reach, float, squirm, and even roll, only animals have developed muscle fiber, which has allowed us to move in a wider variety of ways and heave around vastly more weight. Liu's trails, then, could help unravel the question of when animal life began. Because if something was big and strong enough to create those trails 565 million years ago, it must have had muscles, which means it must have been an animal.

In a neat coincidence, the same summer Liu discovered the fossil trails, he also unearthed a brand-new Ediacaran species with noticeable muscle fibers—at 560 million years old, by far the earliest muscles in the fossil record. While he doesn't believe it was responsible for making the trails, it does provide evidence that musculature was developed earlier than anyone had previously thought. The new species was a ghastly-looking thing, a webbed, cupped hand reaching up from a slender stalk, as if waiting to trap a passing foot. Liu named
it
Haootia quadriformis
, drawing from the language of the island's indigenous inhabitants, the Beothuk.
Haoot
means, simply, “demon.”

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Just as life on Earth requires both reproduction and death for it to evolve, the growth of science requires not just the birth of new discoveries, but the death of old ones. Any new scientific discovery is open to attack—the bigger the finding, typically, the fiercer the attack. Shortly after Liu published the paper outlining his discovery of the world's oldest fossil trails in 2010, Greg Retallack, a professor specializing in paleopedology (the study of fossil soils), attempted to debunk Liu's findings. Retallack claimed that the trails were not the result of animals, but rather “tilting traces,” the marks of pebbles being washed about by the tide. Liu published a swift response addressing each of Retallack's points. Then he invited Andreas Wetzel, the German ichnologist who first introduced the notion of a “tilting trace,” to view the fossil trails in person. Wetzel assured Liu they were not tilting traces.

Around the same time another paper emerged, from a University of Alberta team working in Uruguay, that claimed to have found trails that were twenty million years older than Liu's. This paper was challenged by a team of Uruguayan geologists who argued that the rocks had been dated incorrectly, and that similar fossils had only been found in much younger, Permian rocks. Casting further doubt on their discovery was the fact that the trails were significantly older than Liu's yet relied on a trail-maker with a vastly more advanced body structure. This discrepancy is akin to an automotive historian claiming to have uncovered a flying car from the nineteenth century. It's not impossible, just unlikely. (But then, Liu charitably pointed out to me, his discovery had also once seemed unlikely.)

Such is the gladiatorial, or perhaps more accurately, Darwinian, nature of research science. The goal, as famously explicated by the
philosopher Karl Popper, is that in the competition for funding and fame, any false research will be falsified, and only the strongest theories will survive. However, an unfortunate side effect of this dynamic is what Martin Brasier called the MOFAOTYOF (“My Oldest Fossils Are Older Than Your Oldest Fossils”) principle: “The tendency among all scientists, and certainly among all journalists, is to make their scientific claims as strong as they possibly can from the limited amount of material available.” Bold conjectures are an integral part of healthy science, just as one initially underbids when negotiating at a flea market so as to eventually reach a fair price. But this tendency to exaggerate can prove dangerous, especially when the results trickle out to the general public, who, not understanding that falsification is a necessary part of the game, can develop a jaundiced view of any and all new scientific claims.

When I spoke to Brasier over the phone in 2013, he told me that the uncertainty inherent in this field of research was its appeal: He believed pure science is to be found on the edge of the darkness. “Karl Popper would have said that astrophysics and paleontology are not real science because you can't go out and sample it,” he told me. “I think absolutely the opposite. I think this is actually where science is. It's trying to guess what lies over the hill and map terra incognita. When people come in and colonize, that's just technology.” Brasier believed a scientist was, at heart, an explorer.

One of the strange side effects of working at the edge of the known universe, as Liu does, is that the more you learn, the more uncertain things become. As I talked with Liu and his team, I was constantly unlearning old assumptions I had held; even basic, bedrock knowledge began to disintegrate. What, for example, is the definition of movement? (Does floating count, or must one propel oneself? If so, with what kinds of tissues?) Is “animal” a clear-cut category, or a fuzzy-edged one? What, moreover, does it mean to be a living thing at all?

Life, according to Mikhail A. Fedonkin's
The Rise of the Animals
, a touchstone text among Ediacaran researchers, is defined merely as “a self-perpetuating chemical reaction” or “a self-assembling dynamic system.” The fundamental element of this system is the membrane. Without membranes, there are no cells, and without cells there is no discrete space for chemical reactions to perpetuate. “The cell membrane also allows communication with the outside world, but regulates what comes in and what goes out,” wrote Fedonkin. The communication is imperfect, but that imperfection is what defines one cell from another.

For billions of years, these single cells were the only living things on Earth. However, a cell benefits from better communication and cooperation with other cells. So some cells may have formed symbiotic relationships with others, then gathered into colonies, and, eventually, bound together into tissues. Interdependence both shackles and strengthens. Despite the restriction of freedom, tissues allow a much greater range of body types, including bilateral symmetry (a distinct front end and back end), which is the structural basis for the wild array of beasts that now stalks the earth and sea and sky. Matthews cheekily summed up this billion-year-long process of evolution from cells to bilaterians thus: “Tissues developed because it's nice to have muscles and an ass. It's not good to shit out of your face. It's just not a very good idea.”

We tissuey beings define our individual selves as enclosed, tight-knit systems. (“Otherwise,” Matthews said, “your arm would run away.”) But here too our assumptions begin to break down. As we sat eating our picnic lunches on a flat rock overlooking the sea, Stewart mentioned that he had recently been reading an article in a science magazine that asked what truly defines a human being, since our bodies are dependent on an unseen universe of microorganisms to survive. There are, for example, at least as many bacterial cells as human cells in the human body—possibly many more.

“There are more cells
in
you that
aren't
you,” Matthews said.

“Yeah,” said Stewart. “Which sort of brings you to a point of ‘What
is
you? What
am
I?' I had an existential crisis while I was reading it.”

As I chewed my plum down to its wet-furred pit, a druggy feeling overtook me. I suddenly became aware of my own complexity: a riverine inner landscape swimming with cells both native and foreign; varied tissues clinging to and pulling against an architecture of bone; a digestive tract breaking down a bolus of plant material; two feet pressed against the earth; two nostrils sucking and spouting air; and in between, a branching network of nerves flickering with electricity in a furious effort to make sense of it all. Inside the human body lies a realm of perpetual darkness and riotous life, much of it still unexplored. We are, each of us, wild to our marrow.

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After lunch, we headed east along the shoreline, ascending through geologic time over younger and younger rocks. We were following a stratigraphic chart of Liu's, which looked like a multi-tiered ice-cream sandwich. Each layer depicted a stratum of rock; embedded in some, like a sprinkling of chocolate chips, were known fossils. We paused on one surface where the chart indicated there should be an array of disc-shaped fossils, but we couldn't see them. The angle of the light wasn't right; certain layers reveal their fossils only when the sun is low and shadows become pronounced. Liu got down on his haunches, his eyes scanning the rock. Then they clicked into focus. “Ooh,” he said, pointing. “There's one.” I followed his finger. The lines of an ovoid fossil emerged from the pixelated background, like in those Magic Eye books I used to go cross-eyed over as a child.

“There are loads of them, actually!” Liu said, his hand sweeping across the marbled surface. As his finger passed over them, the outline of a half-dozen other discs rose from the rock.

I was baffled. When I looked at these rocks, I saw a jumbled code: