On any clear night, under a dark enough sky, we can see shooting stars. We wish upon them, even if we don’t quite know what they are—of course they’re not really stars—and even if we don’t know where they come from or what they might tell us about the universe. It’s as if we’re eager to pin our chances on something strange and sudden, something beautiful beyond our ken. Across cultures and time, we have written ourselves into the sky. We create constellations, transforming the random spatter of stars into shapes and stories. We name planets after gods. And we associate meteors and meteorites—the light of dust or rocks burning passage through the air and the stones that, after such fire, sometimes fall to earth—with the most elemental aspects of our lives: good luck, ill fortune, and even death.
These bits of former asteroids have rained devastation in the past and threaten to do so in the future. Impact sites such as Arizona’s Meteor Crater drive home the relationship between falling rocks from space and a fiery inferno that kills every living thing over hundreds of miles—or more. We watch movies with killer asteroids. We can surf the Internet and find sites devoted to the odds of the planet being hit by one earth-crossing rock after another. Clearly, rocks from space are killers, the silent brutes of the solar system just waiting for a chance to sock us. We worry that just as the dinosaurs were clobbered sixty-five million years ago by a cosmic impactor, we’ll be clobbered, too.
While that’s a legitimate worry—scientists are seeking ways to nudge or explode earth-crossing space rocks away from possible impacts—most people don’t know that meteorites, small and large, are also implicated in helping, not destroying, life on earth. A certain class of meteorites called carbonaceous chondrites brim not with living organisms but with water and amino acids, some of the essential stuff for the start of life itself. These meteorites have been falling on our planet since the formation of the solar system, four and a half billion years ago. Even the massive meteorites—iron behemoths the size of train cars, stone monsters the size of cities—even these, after their initial hole-blasting, fire-starting, windstorm-swirling destruction, have created the conditions for life to thrive and to change.
After all, it was the demise of the dinosaurs that cleared ecological niches for a previously minor group of critters called mammals. Thus here we are. And impact craters themselves can become habitats for all kinds of animals. Millions of years ago an impact carved out the Ries Basin in present-day Germany and destroyed an entire region. But in just a century life returned. The crater became a lake teeming with pelicans and snails. The shores became home to bats, hedgehogs, and cattails. Today, researchers in Canada studying Haughton Crater, which formed after a meteorite impact thirty-nine million years ago, have discovered that the stress of the impact created tiny habitats in the form of hydrothermal vents and microscopic fissures.
Meteorites are the alpha and omega of geology. These rocks—mere rocks—encompass the origins of life and the fact of death on our planet. And the most profound lesson in all of this is that meteorites (and comets) don’t always bring death. In fact, one might say: Impact + Heat + Water = Habitat. Call it the Oz equation. Canadian researcher Gordon Osinski—“Oz” to everyone in the meteorite community—has spent several summers with field teams in the Arctic, on Devon Island, where Haughton Crater is yielding clues to how craters can be refuges for microbial life.
“Impact craters,” he says, “still deserve their reputations as scenes of devastation, but as they cool, they become ideal spots for life to reemerge. And this has led some people to wonder if impact craters on the early earth provided the environment for life to emerge in the first place.” Oz notes that some of the planet’s earliest life forms were microbes that seemed perfectly suited for post-impact hot springs and pools, as well as for tiny cracks inside rocks. He cites studies showing that large craters can maintain hydrothermal vents and springs for about one million years after an impact. “This is getting towards the kind of timescale life might need to emerge,” Oz writes. “The warmth of the impact heated groundwater, creating hydrothermal systems” that would have made “perfect homes for intrepid . . . bacteria and algae.” This is a scene that may well have played out at countless craters, even on Mars.
One research team has said that “impact cratering must be viewed as a truly biologic process.” This is an extraordinarily radical turn of events. As recently as 1990, scientists were saying it was possible that “a high rate of cratering hampered early biological evolution on the earth.”
Now, however, some researchers suspect that meteorites have done more for life than create local saunas for recent fauna. It just might be that a meteorite—one hitting what is now Lake Acraman in Australia—forced the most important step in the evolution of life: the jump to complex, multicellular creatures.
To contextualize that jump, we have to go way back to the beginning of what science writer Gabrielle Walker calls “Slimeworld.” It’s not pretty—I mean both word and meaning—but if you’re a single-celled critter whose genetic material sloshes about your cytoplasm, would you care? Probably not.
Arising about four billion years ago from chance meetings of gases, sugars, carbons, proteins, and other morsels—perhaps relatively quickly in a melding of volcanism, carbon, and metals, or more slowly in a chain of prebiotic events in the ocean—the earliest single-celled microbes (empirical miracles known as prokaryotes, which are cells without a nucleus) toughed it out during the Late Heavy Bombardment some 3.8 to 4.1 billion years ago, when asteroids were disturbed from their orbits (the cause of this is not entirely clear) and pulverized themselves against a young planet’s atmosphere and surface, until life’s scummy dominion truly began, with mats of single-celled creatures called stromatolites. They covered the early earth, starting some 3.5 billion years ago and lasting for hundreds of millions of years upon hundreds of millions more, layers of living muck clustered upward in hummocks crowding tidal flats and shores, the world’s first houses, a yard high, built by the world’s first architects, the hundreds of trillions of prokaryotic cyanobacteria upon hundreds of trillions more upon more and more and more. The first green fuse was a wet and teeming tower of blue-green algae. Durable too: A few stromatolite colonies thrive around the world even today.
Prokaryotes of all types are everywhere with us. Without the non-nucleated bacteria in our guts, we’d not be around to read, because we couldn’t digest food. Without the millions of diphtheroid bacteria swarming on your armpits, the toiletries business would swoon.
About one and a half billion years ago, more complex single cells arose—the eukaryotes, cells with a nucleus and other specialized features walled in by membranes. Excepting prokaryotes, all life as we know it is based on the nucleated cell. The nucleus contains an organism’s DNA, and the development of complex internal cellular structures allowed for biochemical and physiological nuance. Eukaryotic cells have advanced organelles, such as the Golgi apparatus, which secretes waste, a kind of microscopic kidney-and-bowel system. Other organelles include the lysosome, which repairs cell damage, and mitochondria, which convert food into energy in animals.
The difference between the non-nucleated cell and the nucleated cell, in other words, is the difference between a flame and an engine.
But, as Stephen Jay Gould once pointed out, it was a very long time before these more complex nucleated cells, these eukaryotes, became organized into multicellular animals. That was the third big leap. Specialization of functions within cells allowed for arrangements of multicellular complexity leading to the array of life around us today.
The first such multicellular animals were part of what is called the Ediacara fauna, which dates from about 550 to 600 million years ago, during the late Precambrian era. This sudden experiment actually preceded the first extensive spread of animal species on the planet by about 100 million years. Which means the Ediacara fauna were like a trailer to a movie, but not the movie itself. Or, some say, like a long-lost ancestor who never fathered a child.
On an afternoon in November 2003, I’m in Brachina Gorge, a canyon in the Flinders Ranges of South Australia. Distant thunder threatens a flash flood. I left Utah and my partner, Kathe, several days ago and am now on a detective hunt for clues to the origins of multicellular life. I’m nearly nose to nose with a few organized ripples on the underside of a boulder, a fossil of Dickinsonia costata, but I’ve not yet found it. It should be here, right where I’m wedged under a cleft of rock, listening to retired University of Adelaide geologist Vic Gostin tell me where to look. Waiting nearby is Lorraine Edmunds, a former park ranger and cheerful naturalist, who has joined Vic and me as a guide. The light is flat, the sky overcast. I still can’t find the fossil. This dun-colored blobby shape? “No, no,” Vic says. He keeps prompting me and waits. Already tired, I grow frustrated. Sand and rocks tickle my back.
Dickinsonia costata was a flat worm with segments spiking out from a bisecting trough, the function of which remains unknown. We do know it had no lungs, that this worm breathed through its skin.
In our world of emus (we’d just seen one as we drove into the gorge) and kangaroos (“Hell yes!” I’d exclaimed when Vic had asked the day before if I wanted to turn around to see my first) and flying birds (galahs, corellas, the melodious Australian magpies) and plants (the muscular river red gum trees) and human beings (new friends in a gorge), in such a world, a worm, flat or tubular, just doesn’t seem, well, all that compelling. Nonetheless, Dickinsonia and its fellow members of the Ediacaran tribe, such as sea pens and jellyfish, were that first, most startling development: They were animals.
With the rank scent of Ward’s weed still lingering in my nose—the lanky, loose, hairy invasive from the Mediterranean has been everywhere in this part of the Flinders Ranges—I finally see it! A hand-sized sunburst of many thin rays, a sundial without its gnomon, hash-marked with lines, not numerals. An interpretive sign here in the gorge compares Dickinsonia to “a segmented doormat.” So welcome home, dude: Set in the reddish Rawnsley Quartzite formation, this Ediacaran worm has been right in front of me for a few minutes. I stare at it, dumbstruck.
Dusty, I clamber up, unsure what comes next. I look about the tight gorge, feeling a curious sense of dualities. Now and the Precambrian. Here and canyons back home. Here in my skin and floating over the world—which begins here at Brachina Gorge, with gray clouds above—and all of it exquisitely real, appearing deceptively, artfully arranged, boulders and the spaces between them, scrubby plants and trees and the spaces between them, the way foreground and background are hyper-real inside old View-Master color reels.
Wind rustles the yellow-flowering mulga, an acacia whose wispiness reminds me of the willows of the American West, including, right beside the Blacksmith Fork River, the peach-leaf willow under which Kathe and I put a hammock in the summer. Here and there, first home, latest home. From beige to brown to orange to cinnamon to oxblood, the rocks of the gorge, only a few yards high, close in. I’m being cupped by the world in time.
And I’ve forgotten the threatening weather, though Vic stands stiffly beside the white four-wheel-drive I rented in Adelaide. The driver’s door is open. Vic knows I’ve come a long way to be here; he answered many e-mails before I arrived and he even met me at the airport, looking every bit the geologist in his jeans, plaid shirt, bolo tie, and purple trilobite pin stuck in his hat. Affable and eclectic, gray hair swept back as if he’s been in wind for years, Vic’s a fine tutor.
Lorraine walks me to some limestone, euphoniously called Wilkawillina, where she wants to show me something else. Wilkawillina limestone is twenty million years younger than the rocks that hold the Ediacara fauna. Despite the ten-year drought in this part of South Australia, despite the need to keep water on hand, Lorraine pours some out of her bottle onto this Cambrian limestone, where psychedelic shapes appear beneath the dark wet. We’re bending over the cross sections of archaeocyaths, creatures that resemble sponges. They appear mostly circular, but also a little blebby, with alternating bands of gray and black. They have, to my novice’s eye, the swirly appearance of agate. Shaped like megaphones, these creatures affixed themselves to the bottoms of shallow seas and formed the world’s first reefs.
“The best in the world,” Vic affirms of these fossils, adding, “Can we get in the car now?”
The thunder’s grown louder. We’re in a gorge. We’d rather not die in a flash flood, so we get in the car.
In a matter of minutes, I’ve spanned two great stages in earth’s history: the late Precambrian era, with Dickinsonia, a mundane worm that, along with its Ediacaran friends, represents the first step into multicellular animals; and the early Cambrian period, with the archaeocyaths, part of the second but by far much larger—and ultimately successful—wave of multicellular life, what is commonly called the “Cambrian Explosion.”
The Ediacara fauna were, many believe, a kind of a cul-de-sac, a box canyon of evolution. Some say all the Ediacara went extinct and, along with them, their unique flat, segmented, and squishy designs, which allowed for large body area but not much in the way of innards. Others believe a few of these species survived to merge into other ancestral lines leading to today’s complex creatures. Some researchers, such as Richard Fortey, are apt to make the e in Explosion lowercase, to emphasize similarities rather than differences in Cambrian animals, and to suggest precursors in the Ediacaran Precambrian.
Later I’ll reflect on the irony. My deepest encounter ever with deep time and life—up close and personal with some of the world’s first critters—and we with our bones and spines and lovers were in a hurry because of a potential storm. One day, back home in Utah, looking at a geological map of the Brachina Gorge trail, I’ll realize that Vic, Lorraine, and I drove right past the 630-million-year-old Trezona limestones that contained fossil impressions of . . . stromatolites. Older even than the Ediacara! I’ll console myself with the prospect of seeing living stromatolites someday, perhaps near San Diego or Yellowstone, and I’ll feel a kind of comfort in knowing that bodies give way to stone and flake, to recorded passage.
In a few minutes, we’re out of the gorge and in an expanse of weird storm light. Shadows blanket hilltops only to peel away and cover a dead-grass plain of mallee and saltbushes. Strata of clouds: altostratus above cumulus. We’re taking the long way back to our cabin, near a circle of mountains called Wilpena Pound—the scenic route, says Vic, though it’s all been scenic to me—and I see distant mountains flatten to gray, then dun, then gray-white against the gray sky spilling virga, then actual rain spatter, dust spatter. I’m sitting in the back, mulling distances and affinities, while Vic talks to Lorraine about his book Environmental Geoscience, while Vic, unperturbed, drives us through what has become a for-real, face-caking (were we outside) dust storm.
Brief tizzy. The storm ends. The sky breaks into fragments dark and sunny, against which wheel little corellas, a spin dizzy of white flakes with wings. The native hematite of the countryside glows red with slanting light. Near a fence we startle a euro, which runs alongside it before lurching its heavy, cartoon body through a hole and bounding away, and we pass Bullock bush heavily grazed by livestock, and I see more corellas and some galahs, and Vic very nearly hits one bird in a flock of red-rumped parrots. I spy a small pale bird of prey, a nankeen kestrel, and all around us bloom tall pinkish spikes of mulla, through which crawl, slowly, sleepy lizards, or “blue tongues,” including this one we’ve stopped for by the roadside. The size of a cat, the sleepy lizard doesn’t move at all. Stumpy-tailed, brown and green, it looks at me with its reptilian stare while Lorraine recounts the guilt she felt for moving one such lizard; it kept eating her strawberries. She learned that they are unique reptiles in that they pair-bond and use the same territory again and again. “Now I share the strawberries,” she says.
Strawberries. Lizards. Euros. Mulla. Galahs. The people who name them. The hard, sweet swarm of life. A dirt road in the outback. Primeval worms and vintage reefs.
Even if the time of the Ediacara fauna was the dead end some think, the Cambrian Explosion assuredly was not. Five hundred million years ago, a hundred million years after the brief rise of the Ediacara tribes, the Cambrian Explosion was the big light switch turned on: the sudden, widespread development and diversification of nucleated, multicellular life. While most of the varied designs of Cambrian creatures have not survived, the Cambrian’s wide-ranging accidental experiments in arranging complex cells set the stage for evolutionary byways that led to, for example, rhipidistians, the first creatures to move from water to land. Among the Cambrian fauna was a wormy little guy called Pikaia: the first creature with a kind of spine. Who’s your daddy? Pikaia.
“In a geological moment near the beginning of the Cambrian,” Stephen Jay Gould once wrote, “nearly all modern phyla made their first appearance . . . The 500 million subsequent years have produced no new phyla, only twists and turns upon established designs—even if some variations, like human consciousness, manage to impact the world in curious ways.”
But why did it happen? Why the expansion of life five hundred million years ago? Oddly, in competing theories that seek to account for the origin of the Cambrian Explosion, the Flinders Ranges of South Australia play a key role.
The day before Vic and Lorraine took me to Brachina Gorge, Vic and I were smearing on sunscreen against the midday glare. We were in the hills past the tiny town of Hawker, amid eucalyptus shrub, spinifex, saltbush, and the ever-present blue-flowering weed called Salvation Jane. I said that South Australia felt a lot like Arizona, only without the cacti. Vic applied a layer of zinc paste to his red nose, whose color had resulted from the loss of melanin after he underwent treatments for cancer a few years ago. Like other such survivors I’ve known, he has a lightness of being that seems at once accepting and hungry.
In a minute or so, I found myself trying to keep up with Vic—physically and conversationally—while we walked in a dry creek bed and avoided kangaroo droppings. I wanted to head toward some meager shade cast by white cypress pines and river red gums, but we stayed in the sun to look at some rocks. We were heading into what was once a Precambrian shallows, a marine delta where the water had been placid, a place from some 680 million years ago, before even the Ediacara fauna had appeared. Vic punctuated geological riffs with the endearing phrase “wow, man” and told me stories.
It was in this ravine that Vic’s fellow Australian geologist George Williams had found small crinkles in pinkish mudstone. I bent to touch these gentle ridges and depressions. I might have mistaken the ridges for the record of glacial striations, but that’s not what these lines of bumps record. They were, Williams deduced, the accumulation of tidally deposited sand—tidal rhythmites. Williams drilled core samples on the small rise just before us and discovered that the fortnightly tides had occurred at this rate all over the planet.
“Tides are like drums in the orchestra,” Vic said. “You can hear music, but you can also find the rhythms underneath.” The wind shushed through the brushstroke branchlets of the drooping she-oak, and Vic told me more about the Precambrian world.
The moon at that time loomed larger in the sky because it was several thousand miles closer to the earth, which, of course, made for stronger tides. The earth’s orbit and spin were slower and faster, respectively. A year was a month longer than it is now, a day a couple of hours shorter.
Williams found other rocks from that era besides the rhythmites. He had investigated rocks whose original magnetic fields were horizontal, meaning the rocks originated at the equator. But here’s what baffled a few researchers: At the time, the equator was, some say, icy cold. The huge moon gleamed over glistening equatorial ice and, it seems, pools of open water where the tides moved.
There was more: Williams found sand wedges—gaps created by freezing and thawing into which dirt blows. Their significance is simple: To get freezing and thawing you need seasons.
How to explain open water and equatorial ice and seasons? Did all things coexist in the Precambrian era? Some say yes.
Williams champions a theory called the Big Tilt. He argues that Precambrian earth was tilted such that the present-day poles were closer to where the equator is and vice versa. Something had whacked the earth—over four billion years ago when another planet hit the earth, causing the formation of the moon—then, over time, the earth came to its present orientation.
There were more mysteries. Brian Harland discovered carbonates—right next to where there had been ice. Carbonates come in a wide variety, but the important point here is that they form in warm water. Gabrielle Walker compares Harland’s findings to “watching a glacier march across Barbados.”
So, how to explain open water and equatorial ice and seasons and warm-water carbonates? This is a “wow, man” sort of world. Eventually, Cal Tech researcher Joe Kirschvink dubbed the whole shebang “snowball earth.” Since Kirschvink, others, most notably Paul Hoffman, have taken up the snowball earth theory. Simply put, it suggests that nearly eight hundred million years ago, with the fracturing of continents clustered near the equator, “formerly landlocked areas [were] . . . closer to oceanic sources of moisture,” according to Scientific American. “Increased rainfall scrub[bed] more heat-trapping carbon dioxide out of the air,” leading to cooler temperatures, the spread of polar ice to middle latitudes, and increased reflection of sunlight and heat into space. The effects cascaded into a global ice age, which ended only after enough carbon dioxide had vented from volcanoes into the air, leading to a thaw. The whole process took millions of years. Another catalyst for starting the snowball earth might have been the sun, which did not shine as hotly and brightly hundreds of millions of years ago.
As to evidence of seasons at the equator—the sand wedges, which Williams believes militates against snowball earth—others have found that far from banishing the seasons, an icy planet may still have had variations in temperatures. Further, Hoffman and others believe the earth suffered a series of snowball episodes with the last thawing prior to—you guessed it—the Cambrian Explosion. Snowball advocates say that microbial life toughed it out in a few places on the icy earth, such as deep-sea, hot-water vents, and that when the snowball melted, these hardy critters were primed to diversify. It might also have been the case that there was some open water during the last snowball—another refuge for microbes.
There is, however, the matter of a several-million-year gap between the end of the last global ice age and the appearance of the Cambrian Explosion. In fact, as of 2007, Hoffman had softened his claims: “It would seem that the achievement of multicellularity in (microscopic) animals would be the evolutionary step most closely associated in time with the [last] . . . snowball earth. However, there is as yet no empirical support for this in the fossil record.”
So what forced the Cambrian Explosion? The righting of the planet following the Big Tilt? The thawing of snowball earth? Something called “true polar wander,” which suggests that imbalances in the earth’s mantle forced continental movements that drove ecosystem changes?
Paleontologist Kath Grey, who is, according to the Australian Centre for Astrobiology, the “undisputed world leader” in the study of early fossil planktons, thinks it was something else, and here is where the Oz Equation seems writ large. Grey believes she has found evidence that the Cambrian Explosion has a different cause: a meteorite impact in what is now South Australia. The meteorite—a very big one, some three miles wide—hit roughly 580 million years ago, creating a fifty-six-mile-wide crater in old volcanic rock. Big enough to alter the global climate.
In a lovely irony, the remains of the Lake Acraman crater were first discovered, years ago, by snowball earth critic George Williams, at about the same time Vic Gostin was puzzling over strange chunks of rock in the Flinders Ranges. Now Grey thinks the timing of the Acraman impact—long after the last snowball melted—sparked the first extensive rise of life on earth. The Cambrian Explosion may have been more aptly named than we knew.
Vic and I headed back to our car that afternoon, both of us anticipating our coming flight over the Acraman impact site, which, if Grey is right, may come to be seen as a kind of fiery Eden.
I wake to flanks of billowed clouds, sky and clouds colored gray, blue-gray, blue, pink, silver, the outback freshly scrubbed with last night’s rain. Leaves drip. The “flute-like caroling,” as my field guide puts it, of the magpie, echoes and braids as I spend part of the morning alone, away from the small hotel and campground where Vic and I are staying at Wilpena Pound. In the quiet and song, my mind registers impressions: ringneck, rufous whistler, red-rumped parrot, white-browed babbler, magpie-lark, and the swamp harrier, which, for twenty minutes, perches across a field in a grove of white cypress pines, as if the stillness that precedes satiation redeems it.
Vic, Lorraine, and I eventually gather only to wait a few hours for the last of the weather to clear, then, a little after 2:00 p.m., we’re clambering into the Cessna 180 that Wilpena Pound Resort uses for tourist flights. We’re going to fly over Acraman.
We climb to 4,500 feet, and Lorraine tells me that all the crisscrossing lines in the dirt below are ’roo tracks and rabbit warrens. Then our pilot, Melissa Hosking, swings us past the southeast corner of Wilpena Pound, which, at about 3,700 feet, is the tallest part of the range. The mountainous Pound is shaped like a bowl that looks dramatically more like a meteorite crater (which it’s not) than will the seasonal wetland that is Lake Acraman. The Pound was formed by sediments built up in the Precambrian and Cambrian seas that folded, then eroded to its present shape. It takes fifteen minutes to pass by the Pound, and sun beats on the plane.
Soon, Lake Torrens is ahead, a strip of white on the horizon. As we pass over orange-red sand dunes, I lean my head around even though we’re all wired with headphones.
“It looks like Mars,” I say to Vic.
“Bull dust,” he calls the fine sand down there.
Now come the gypsum dunes of Lake Torrens, one of the several seasonal, salty lakes west of the Flinders. To my right, to the northeast, are the Ediacara Hills, first known home to the fossil animals I met at Brachina Gorge. The landscape below remains orange and dun, dotted with black oak and saltbushes and porcupine grass—spinifex. Below us, as we fly west, the sandy deltas of the Torrens Basin. The ground blurs: pale sand, cinnamon sand, brown sand. But last night’s rains gifted Lake Torrens, where, much to Lorraine’s surprise, there’s some patchy water. We see a pale gray-blue sheen reflecting the clouds. It looks a bit like the braiding of wet and dry land that fringes the Great Salt Lake.
While Vic reels off facts about crust thickness, faults, and erosion rates, the heat and bumpy thermals make me queasy. I force myself to look at Melissa’s charts. We’re over the Andamooka Ranges, Burden Hill, others. Pernatty Lagoon slips by, and fifty miles from Acraman, I look down on a striking series of parallel ridges and dunes south of Gairdner, then the salt flats of Lake Gairdner itself, which are so extensive I feel as though I’m visiting a place I’ve seen before—of course. I’m flying over Thule again. I’m back north, north of the Arctic Circle, a place I visited during my journeys to write a book about meteorites, a place where explorer Robert Peary had stolen giant iron meteorites from the Inuit. So below is the Greenland ice cap, rendered in desert salts. Despite my mounting nausea, I am entranced. I’m subatomic, wave and particle, two things at once in two places at once. An outback ice cap.
It was in 1979 that Williams saw the circular shape of Lake Acraman in satellite photos and quickly suspected a meteorite impact. A few months later, he collected samples from the 1.6 billion-year-old volcanic rock that makes up the region: The rocks contained shocked quartz. Williams had indeed found a meteorite crater, old and eroded but still Australia’s largest. At the time, though, more concerned with mineral exploration for a company, he didn’t publish his findings.
Not long after Williams had drawn his conclusions about Acraman, Vic was in the field, not far from Wilpena Pound, confronting a mystery. Vic had found a grainy layer of volcanic rock intermixed with a formation of sedimentary rock laid down by an ancient sea; he thought the volcanic material was similar to the Gawler Range Volcanics hundreds of miles away, where Williams had spied the Acraman crater, though, of course, Vic didn’t know that yet. Might the volcanic rocks be glacial erratics? he wondered. Or brought in by some other means, such as river deposition? Vic didn’t think so, but was trying to consider all possibilities. Further fieldwork, as well as study of samples, showed Vic and his students a continuous layer of volcanic rock through much of that part of the Flinders Ranges. Strangely, the volcanic rock had undergone, as Vic writes in his notes, some form of “gross alteration.”
Expecting the volcanic rocks and the marine shales to be contemporaries of each other—perhaps, most simply, a volcano near the ocean had spewed those rocks out—Vic was baffled to learn that the volcanic fragments and the marine shales were vastly different in age: The former were some 1.6 billion years old, the latter only about 580 million years old.
Doubts nagged him. In 1985, he had been reading the work of spiritual leader Krishnamurti and told himself to clear his mind of prejudice and relax. He doesn’t recall if he was in the field or at home when, wide awake one night, he reviewed everything in his mind. Volcanic material in one layer. Fallen off cliff? No cliff high enough or near enough. River deposit? No, the Bunyeroo mudstone shale is marine—a sea, not a river. Debris flow? The sediments didn’t fit that. Glacial? The rocks showed no glacial scratches. There had been a surface explosion, a huge one, in an area of ancient and uniform lithology.
Did it fall out of heaven? he suddenly asked himself. The recent paper by the Nobel laureate Luis Alvarez, about an impact at the Cretaceous-Tertiary boundary, had been on his mind.
The next day Vic and his graduate students put a rock sample under a microscope.
“I wind up the magnification on a thin section,” Vic says, remembering how he suddenly discerned tiny sets of lines in the sample. He and his students now had PDFs—planar deformation features—shock lines in glass, usually formed by an impact. “Hey, this is part of the shock, the bang, the hammer hit!” Vic realized. “We were delirious.”
Doctoral student Peter Haines even found microscopic shatter cones—rock that was rearranged by pressure from the impact. And the area around Wilpena Pound—where the impact had spewed its nasty mix of remelted old volcanic rock and a mish-mash of meteoritic material—was full of big rocks that had been blown out of a crater: impact ejecta. The volcanic rock was early Precambrian, and the impact itself had taken place in the very late Precambrian era, when the area was likely iced up. Vic, Peter, and their coworkers soon learned that Williams had quietly discovered the Lake Acraman impact site.
In 1985, Vic told Williams of his findings. Vic’s ejecta blocks, Williams writes, “matched, both in general rock type and degree of shock metamorphism . . . [the] shattered rocks I had collected from Lake Acraman.” The next year Williams and a team led by Vic published two separate articles—one on the Acraman impact structure, the other on the ejecta—side by side in Science. Three years later, Vic, Reid Keays, and Malcolm Wallace announced that the Acraman ejecta had high cosmic iridium content—just like the iridium spike at the Cretaceous-Tertiary boundary—and to this day iridium, which is rare on earth, helps scientists to tag impact events.
At the time, Chicxulub, the impact site for the K-T bolide, had not yet been found, and paleontologists were still up in arms that scientists from other fields had invoked a massive meteorite as the ultimate cause of the dinosaurs’ demise. The Acraman impact had nothing to do with the dinosaurs (they weren’t around then), but the timing of the Acraman findings helped swing the scientific community toward accepting impacts as normal parts of the earth’s history—even one as bewildering as Acraman.
This huge meteorite hit at a velocity of fifteen and a half miles per second, producing an explosion far larger than the biggest atomic blast, hurtling rocks outward for hundreds of miles as well as sparking tidal waves. The impact sent dust around the world.
Vic and Lorraine had shown me ejecta exposures the day before our flight over the crater. In billboardless country where yellow-flowering twin-leaf and pink clover grow, Vic had driven us around the Flinders, including the ABC Range (twenty-six peaks, twenty-six letters). At one exposure, where I crushed lemongrass to rid my nose of the musky smell of Ward’s weed, the three of us stood in front of a short, steep slope of eroded shale scree. Crows called. White cypress pines grew on the ridge. There before me was the odd stippled rock, the gray-green shales whose mostly flat tops were faceted by erosion. Within the shales occurred nubbly ejecta, almost like lumpy cookie dough, only finer. Lichen had stained the sandpapery ejecta mostly black, though it also showed stains of maroon or brick red. I picked up loose rock that was former meteorite, former lava, former ocean. Sun glared, and I sweated up a storm. It was as if I held the Grail.
A white strip on the horizon, a bull’s-eye in the Gawler Range Volcanics. Lake Acraman. Ground zero.
We fly toward the edge of Acraman, which is speckled with thick vegetation and eroded dacite outcrops like scabby blisters. Dacite is a quartzy volcanic rock, here appearing gray from the slow growth of lichens. This was the rock that the impactor struck 580 million years ago.
The Cessna banks above this huge wound in the earth. Vic is excited, and I’m trying to see if my attempts at geological perspicacity can trump or at least stave off regurgitation, especially now that Melissa is dropping the plane closer to the crater. The temperature climbs as we descend—it’s damn hot—and my body feels full of magma.
Lake Acraman looms. The entire astrobleme, now twenty-three miles wide, is the eroded remnant of the crater’s central zone, including the central uplift—the peak in the middle of any large crater caused by rebounding molten material—and thus, because of the wear and tear over the ages, the crater is now more properly called an impact structure. Terms aside, the place looks painterly, an impressionist’s modello, with snaking channels, ponds, wet curves along the crater’s south edge, depositions of sand that paisley the crater with islands, and trees like black flecks of smashed insects. I’m wishing we could land, though I know we can’t, and I recall Williams e-mailing me before my trip to warn in ALL CAPS to NOT drive this area in the HOT Australian spring. That I would die.
We dip toward the dacite outcrops on the shore and on islands where Williams had taken his samples years ago. I envy him his pick-and-hammer solitude, his under-the-stars notebooks. In the distance the low-lying, eroded hills of the Gawler Ranges partially ring the crater, and sand dunes nestle closer to the lake bed itself. The area is now a protected geological sanctuary.
In the cockpit, sunlight flares against the dark dashboard, and so, sweating, unable to write notes, I take photos that will turn out almost as blurred as the “lake” below, that sandy, watery, wattly mixture which seems more marsh than crater. Perhaps the hazy quality of the sky and the land and my body is appropriate: the blurring of this into that, then into now.
After the initial flurry of Acraman impact papers in the 1980s, interest waned. The Acraman story, it seemed, was complete. But in May 1998, Vic had lunch with Grey, who told him that the Acraman impact, based on what the fossils were telling her, seemed curiously timed.
Here’s why. As Grey and her coauthors Malcolm R. Walter and Clive R. Calver would go on to point out in a 2003 study in Geology, right after the 580-million-year-old Acraman “debris layer,” there came a veritable torrent of speciation. Some fifty-seven new species of plankton appeared. And they were different. Before the Acraman impact, most plankton were “simple spheroids.” But after the Acraman impact spread its globe-trotting dust blanket, which surely limited photosynthesis, something strange happened: The plankton changed. They grew complex spikes, spikes that apparently protected them from hard times on earth. These “acritarch” planktons were among the first eukaryotes, and they evolved from their more primitive spheroid kin. While there had been a few species with spikes before Acraman, they had been in the distinct minority then. These post-impact spiky plankton were bigger and more complex—and they became dominant.
Grey, Walter, and Calver also point out that this evolutionary burst “did not happen until long after” the end of snowball earth. “Post-glacial species [are] identical to pre-glacial ones,” Grey writes in an article in Australasian Science. “There was no post-glacial colonisation by rapidly diversifying species.”
So ten million years later, ten million years after the last snowball earth episode (if there was one, which some doubt), the Acraman bolide screamed out of the sky. The post-Acraman darkness and consequent cold clamped down hard on bacteria. According to Grey, “Organisms dependent on photosynthesis, such as . . . [simpler spheroid plankton] were devastated, but the event had less effect on a small population of spiny acritarchs, which produce protective shells or cysts when conditions are adverse.” Then, eventually, conditions eased. That’s when Grey’s spiky planktons went wild, as they were able to recover faster than the harder-hit spheroid bacteria. This sudden rise in plankton diversity probably widened the bottom of the food chain, in turn helping to spur the evolution of other animals. Grey believes that the last big glaciation prior to the Acraman impact must have served as a crucible for microbial life, but its end was not enough to spark the first great flowering of life on earth, the “Cambrian diversification,” which, she and others think was aided by the impact in “a baptism of ice and fire.”
The work behind this discovery was painstaking. Relying on core samples made across the country in the search for oil, Grey used acid to isolate tiny bits of organic material. Looking through a microscope, she says, she found that the samples contained “hundreds of bacterial spheres and filaments, fragments of benthic (bottom-dwelling) mats, and planktonic green algae,” the latter consisting of two types—“simple spheres” and “large spiny forms.”
Grey adds that when she began she “had no idea of what we were going to find.” The project had been an effort to develop dating of Precambrian strata. But Grey kept discovering heretofore undescribed microscopic fossils. She worked with thousands of samples, and did so on weekends and at night because the research was not directly related to finding fuel and mineral resources, which was the focus of her government position. The study took years, and Grey eventually published a massive, seven-hundred-page monograph detailing her finds.
The rise of spiked plankton after the Acraman impact was her biggest surprise. “When I first plotted up the results,” she says, “I could not believe what I was seeing.” Her thesis supervisor, Malcolm Walter, didn’t believe it, either. So Grey started over, examining all the slides again and relogging data, but the Acraman correlation wouldn’t go away. Then she learned from Clive Calver that after Acraman, there had been a global die-off of many other tiny creatures.
Snowball earther Paul Hoffman wasn’t impressed, however. While he admitted to New Scientist magazine in 2003 that Grey’s Acraman theory was “a great idea,” he also insisted it was “very testable.” “If you find one place where there are big spinies before the impact layer,” he told the magazine, “the hypothesis is wrong.”
Grey counters that this “idea that a single spiny species before the event would negate the theory is not correct. I would actually expect to see a few spiny species around before the event. Not many, and in low numbers, but they should be there. The [impact] event would effectively wipe out much of the competition, allowing the spiny forms an advantage. After all, the mammals were around but not very significant during the age of the dinosaurs, just before the K-T event.”
Much more remains to be done if Grey’s theory is to be proven correct. She concedes as much, saying the evidence to back Acraman as an evolutionary catalyst is “largely circumstantial and requires further testing.” Moreover, some of her colleagues think that the simple spheroid bacteria could have produced a coating to protect themselves from harsh conditions. Grey disagrees. She believes there is microscopic evidence that the spheres were “dividing,” which implies that they had “soft cellular walls” rather than hard exteriors like that of the spiny plankton.
In 2007, four years after my visit to Australia, Grey will tell me that she and others are finding new evidence to support her theory. Sebastian Willman, a Swedish doctoral student, has studied more South Australian drill holes (either ones Grey has not examined or only preliminarily) and has not only confirmed the sequence of events in Australia, but also identified new species. Identical species are known to be present in Siberia and near the Ural Mountains, and while the exact age of these successions is unclear, they can be matched to the ones in Australia. The species from these other parts of the world show the same changes in plankton populations as Grey’s original data did. At the time of Grey’s first study, the actual ejecta layer was known in only three drill holes, but she, Willman, and Andrew Hill will go on to find the changing plankton in other core samples from other drill holes in Australia. Researchers will also see suggestions that the Acraman impact had a major effect on organic chemistry. But it’s not yet been possible to match the Australian, Siberian, and Ural Mountain plankton changes to those of a supposedly similar age in other parts of the world, including China, the Himalayas, and Norway. Grey thinks this could be a function of different forms of preservation, slight differences in ages of the rocks, and varied kinds of sedimentation. Additional study is needed.
Hoffman, on the other hand, will focus on those specimens from China and elsewhere, noting that an “abundant” number of spiny planktons there date closer to the end of a glacial period—preceding the Acraman impact—and that a chemical tracer linked to ancient sponges in Oman also predates Acraman. He will tell me that “these recent discoveries . . . make it more likely that early animal evolution was connected to global glaciation” rather than the Acraman impact.
But Grey can’t find any other way to explain what she’s found. Her observations fit perfectly with the emerging paradigm of craters as refuges—and fountainheads—for life, and even Hoffman will admit, “The story is far from over.”
We’re leaving Acraman behind. I look up frequently to reclaim horizon, seeing only a few faraway cotton-puff clouds and the Gawler Ranges to the south and west. Then I steal a few more glances down, where the patina of cumulus shadows the beige sand and washes of salt. Melissa turns back east, and the shore of Acraman recedes.
There my notes end. I fall asleep in the plane until Vic wakes me up for an impressive, late-day view of Wilpena Pound, which, while more immediately stunning than Acraman, does not conjure up the same mélange of images in my head: hot, wet water in a silty crater; slides of plankton; a dark, fire-shot column.
On our first evening at Wilpena Pound, Vic told me that Grey’s research is “the resurrection of Acraman”—he used the present tense, meaning that this was not only a singular event but also an ongoing story. And the day before our flight, when Lorraine and I had been examining more ejecta chunked into shale, I had come across a tiny fern growing in the shade of the hand-sized rock, about the last thing I expected to see in the desert.
“What’s this one called?” I asked Lorraine.
“A resurrection plant,” she told me.
“Oh!” I said, reaching down to touch the gray-green leaves. “That’s perfect!”
Resurrection plants live beside and under rock edges and in clefts, to take advantage of whatever water might collect there. That tiny plant, nucleated down to the last drop, had hunkered among meteorite ejecta, shale, mosses, and meager shade, its thin leaves arrayed against oblivion. Doesn’t chance alone seem miracle enough?
After all, catastrophe in its original Greek means, simply, “a turning.”
At dinner one night, I asked Vic if he thought Kath Grey was correct, if Acraman really was the most important crater on the planet.
“That’s right,” he answered, nodding vigorously. “It’s creation out of destruction.”
Photo © Todd Kemper /Todd Kemper Photography, www.kemperphoto.com