The Ends of the World

Peter Brannen

• Publisher: Oneworld Publications
• Year: 2017
• ISBN:
  9781786070081
• Topic: Biological Sciences
• Subtopic: Global Warming & Climate Change
• Index: Biological Sciences

'A book about one apocalypse – much less five – could have been a daunting read, were it not for the wit, lyricism, and clarity that Peter Brannen brings to every page.' Ed Yong, author of I Contain Multitudes Apocalypse, now?Death by fire, ice, poison gas, suffocation, asteroid. At five moments through history life on Earth was dragged to the very edge of extinction.Now, armed with revolutionary technology, scientists are uncovering clues about what caused these catastrophes. Deep-diving into past worlds of dragonflies the size of seagulls and fishes with guillotines for mouths, they explore how – against all the odds – life survived and what these ominous chapters can tell us about our future.

1

BEGINNINGS

We have a sense that the beginning of animal life on our planet was like a dawning spring. But the reality is that the age of animals was like a baby born to almost impossibly old parents.

—Peter Ward

I’m from Boston. Conveniently, this means it’s only a short commuter ferry ride across the harbor to see what might be some of the earliest fossils of large, complex life in the history of the planet. Below a marina ringed with condos and the trappings of strip mall modernity is a beach studded with the rusty spikes of some bygone wharf. At the far end of the neglected beach, low tide reveals slabs of ancient seafloor draped in seaweed, sloping into the sea. The rocks, from the bottom of the ocean off the coast of a supercontinent near the South Pole, poke out not far from the Bed Bath & Beyond parking lot. They are more than half a billion years old. No plaque or marker indicates that there’s anything particularly interesting about them, but brushing back the wrack reveals concentric ovals, no larger than a quarter, that pock the surface of the stone. The unassuming rings in the rock might mark the imprint where a fern-shaped creature anchored itself to the slimy silt at the bottom of the ocean at the dawn of complex life.

This is where the story starts. On a planet that shares our name, but that’s about it.

It’s impossible to grasp how long ago these creatures led their strange lives on the Antarctic Boston seafloor. It’s doubly impossible to grasp how old the planet is—or how insignificant the role humanity has played on it. With his paean to “the Pale Blue Dot,” Carl Sagan helped illustrate how utterly marooned we are in our tiny, far-flung corner of space. But we are similarly marooned in time, between incomprehensible eternities. Luckily, geologists have come up with some mental tricks to help us grok our place among the eons. One of them involves a footstep analogy* that goes something like the following: imagine each step you take represents 100 years of history. The simple conceit has stupefying implications.

Let’s begin our walk; we’ll start in the present and head back. As you lift up your heel there’s no Internet, one-third of the earth’s coral reefs reappear, atomic bombs violently reassemble, two world wars are fought (in reverse), the electric glow on the night side of the planet is extinguished, and—when your foot lands—the Ottoman Empire exists. One step. After twenty steps, you stroll by Jesus. A few paces later the other great religions begin to wink out of existence: first Buddhism, then Zoroastrianism, then Judaism, then Hinduism. With each footfall, the cultural milestones get more staggering. The first legal systems and writing disappear, and then, tragically, so does beer. After only a few dozen steps—before you can even reach the end of the block—all of recorded history peters out, all of human civilization is behind you, and woolly mammoths exist. That was easy. You stretch your legs and prepare for what couldn’t be much longer of a walk. Perhaps it’s a short stroll to the dinosaurs, and a little farther still to the trilobites. No doubt you’ll be at the formation of the earth by sundown. Not so.

In fact, you would have to keep walking for 20 miles a day, every day, for four years to cover the rest of the planet’s history.* Clearly the story of planet Earth is not the story of Homo sapiens. Almost all of that walk would be through a forbidding landscape with no complex life on it whatsoever. Not in the deep sea, not atop the mountains, not in the tropics, nor on the endless barren granite interiors of the continents. Save for the wind and the waves, ours was a silent planet for the most part during this nearly eternal preamble to animal life. Those first creatures, stamped in the rocks of Boston Harbor and elsewhere, came after 4 billion years on Earth without anything on the entire face of the planet more exciting than pond scum. In fact, the years between 1.85 billion and 850 million years ago were so uneventful that even geologists have taken to referring to them as the “boring billion.” When a geologist calls something boring, reel in horror.

As we search for life around other planets this is something to keep in mind: even the earth was a desolate wasteland for 90 percent of its history. In fact, one of the only signs of life in the rock record for billions of years is the presence of uninspiring mounds of fossilized microbial slime. Then, around 635 million years ago, a tiny whisper of complex life: rocks found in Oman bear 24-isopropylcholestane, a mouthful of a chemical that today is produced only by certain sponges. Sponges got busy filtering the sea and burying carbon and thus may have ventilated the oceans, making more complex life possible. As the Smithsonian’s Doug Erwin writes, “Humanity owes a special debt to sponges.” Something to keep in mind the next time you’re using one to wipe bacon grease off a pan.*

Then, around 579 million years ago, during the Ediacaran period, after a spell of near-sterilizing global ice ages (aptly called Snowball Earth),^† the champagne bottle of life was uncorked and large, complex creatures finally, and rather suddenly, appear as fossils on the ancient ocean floor.

Although this is still recent history in the 4,500-million-year life span of the planet, it’s still unspeakably old—more than 200 million years before the supercontinent Pangaea assembled, and more than 500 million years before T. rex. And at 579 million years ago, it’s about 579 million years before modern humans, whose years on this planet are measured in hundreds of thousands rather than millions. Even for geologists, these abysses of deep time far surpass all understanding.

The first simple creatures that suddenly appear in the fossil record were probably not animals at all. And their reign would be a short one. In fact, they might have endured the first mass extinction ever, leaving only their cryptic shapes in the rocks, their lives discernible only through the poetry of paleontologists.

Across the windswept “hyperoceanic barrens” of southeast Newfoundland, and not far from the lonely telegraph station that picked up the last distress signals of the HMS Titanic, is still more fossil graffiti left on old ocean rocks by these pseudo-creatures—hieroglyphic echoes of life in the perpetual midnight of the ancient deep. Some of the Newfoundland fossils recall fern fronds, feather dusters, and slender cones, while others appear as large, Seuss-like segmented slugs or bloated centipedes. They seem to have invented a way of life—a mostly immobile one—unlike anything alive today: sluggishly sucking up organic gunk in the disgusting seas of the primordial earth across their membranes. But this way of life was a failed attempt at life on earth. By the next age all these creatures would be gone.

Around 540 million years ago, the Ediacaran world was destroyed—dramatically swept aside in the most important moment in the history of evolution: the Cambrian Explosion. When this spectacular supernova of biology detonated, the world of animal life—creatures that move around and eat other organisms for a living—was truly born. Though there are fossil whispers of an emergent animal lineage in the staid age that came before, the turbid seas had been dominated until then by the almost inert, fractal pseudo-creatures of the Ediacaran period. That all changed at the dawn of the Cambrian. Animals rapidly diversified and overthrew this weird life with a menagerie of even weirder life. Though it hasn’t been inducted into the ranks of the canonical Big Five mass extinctions, the Cambrian Explosion, counterintuitively, might have also marked the first such mass death in the history of complex life.

If the forgotten creatures of the Ediacaran period in Newfoundland and elsewhere look like graffiti left by aliens, then the flamboyant animals of the Cambrian Explosion that replaced them look like the aliens themselves. The seas were suddenly stocked with creatures that would be difficult to invent during the most frenzied acid trip—indeed, one Cambrian animal is even named Hallucigenia. Another, Opabinia, with five eyes and a bizarre armlike appendage where one would expect a mouth, drew peals of laughter when it was first described at a scientific meeting. Still others, like the iconically weird Anomalocaris—looking something like an undulating, satanic lobster—invite us to squint when imagining its place on our common tree of life. Their unrecognizable forms, now entombed in museum displays and tantalizingly rendered in artists’ depictions, stand as reminders that, though it was still technically “Earth,” this planet has been many altogether different worlds over its lifetime.

Some of these animal experiments were just that—experiments. And some experiments fail, never to be reproduced again. Others were more successful: on the bizarre roster of creatures from the Cambrian Explosion is an ancestor of ours, perhaps the unimpressive 2-inch, lancelet-like Metaspriggina.

The widespread appearance of animals starting in the Cambrian period is so startlingly abrupt in the fossil record that its seeming spontaneity worried Darwin. The more than a century of investigation since has shown that the explosion wasn’t quite so instantaneous, but from a geological perspective it was still shockingly swift. The causes of the explosion are still hotly debated. They range from an increase in oxygen in the oceans (possibly a product of life itself), which would have underwritten the more energetic lifestyles of animals, to more speculative causes, like the invention of vision, which would have suddenly illuminated the zero-sum playing field for predators and prey, lighting the fuse of a predatory arms race. But lost amid the hubbub of the Cambrian Explosion is the sad story of the brief world that came before and whose mysterious, forgotten forms vanished forever. When animal life exploded, those strange fleshy fronds at the bottom of the ocean and bloated sluglike creatures would never be seen again.

“It was a mass extinction that was ultimately caused by the evolution of new behaviors,” said Vanderbilt paleontologist and Ediacaran expert Simon Darroch. I caught up with Darroch at a geology conference in Baltimore. A fresh-faced and affable scientist who speaks the Queen’s English, Darroch sticks out among the crowd of goateed, mildly autistic, middle-aged, midwestern American males that haunt stateside geology conferences.

The disappearance of the strange world that preceded the Cambrian Explosion—a zen garden world of unfamiliar fractal creatures rising from the seafloor and strange quilted blobs hugging the microbial mats—has long been a mystery to paleontologists. But in 2015, Darroch and his colleagues declared the cold case to be a mass extinction.

“We think of mass extinctions as requiring an abiotic driver: an asteroid impact or a period of volcanism. But here there’s strong evidence that biological organisms that changed their environment drove the extinction of vast swaths of complex, eukaryotic life. I think it’s a powerful analogy for what we’re doing today.”

One new behavior in particular seems to have been responsible for much of the disruption: burrowing. The strange geometric creatures in Newfoundland and elsewhere depended on revolting, organic-rich murky seas, along with seafloors paved with undisturbed microbial muck, to survive. But when the Cambrian Explosion went off and animals inherited the earth, they began churning up the seafloor. For the strange quilted blobs of the former Ediacaran period that sat on the bottom and absorbed the nutrition from the placid sheets of slime, this was catastrophic. In fact, burrows in the rocks officially define the start of the Cambrian period for geologists. They might have been left there by so-called penis worms (no kidding), which churned through the primeval seafloor and ruined the Ediacaran habitat. For geologists, the burrows mark a qualitative change in the strata, separating it from the billions of years of unburrowed rocks that come before. And it’s a change perhaps unmatched in the rock record for the next half-billion years, until humans began leaving miles-deep holes in the rocks, in search of minerals and fossil fuels.

The animal arrivistes of the Cambrian Explosion also began filtering the seas and delivering ever more organic carbon that had been suspended in the water column to the seafloor. In other words, they started pooping. As a result, the strange fractal fronds of the preceding Ediacaran period were suddenly left suspended in a frightfully clear sea with nothing to eat.

The flip side of this new Cambrian animal menagerie taking all this carbon gunk out of the water and burying it in the seafloor might have been an even greater boost of oxygen in the ocean. This boost might have further fueled the arms race of innovation then escalating in the seas, leaving the poor sluggish pseudo-creatures behind. By ventilating the oceans, animal life was making the planet ever more habitable for more animal life and prodding ever crazier experiments in biology. What hope did a quilted blob or a motionless fractal frond have in a world that was weaponizing with tentacles and exoskeletons and claws?

A sentiment exists—particularly among nonscientists—that the idea of humans seriously disrupting the planet on a geological scale is mere anthropocentric hubris. But this sentiment misunderstands the history of life. In the geological past, seemingly small innovations have reorganized the planet’s chemistry, hurling it into drastic phase changes. Surely humans might be as significant as the filter-feeding animals of the Cambrian Explosion.

“It’s not mind-blowing stuff, but I think it’s hard for people to accept because we don’t see ourselves as that important in the grand scheme of things,” Darroch said. “But here’s an example where, 500 million years ago, something very similar happened. There’s plenty of talk today about comparing rates of extinction in the mass extinctions of the past with the rate at which we’re driving species extinct today, and it’s all through the evolution of new behaviors and ecosystem engineering.”

Like the Cambrian burrowers that reshaped the microbial mat world to their own ends, humans have converted half the planet’s land surface to farmland. We’re even beginning to change the chemistry of the ocean, acidifying it with carbon dioxide and turning whole swaths of the continental shelves anoxic with the deluge of nitrogen and phosphorus fertilizers pouring out of our agricultural heartlands. And the dizzying arsenal of our modern technology is a leap in innovation perhaps matched in the entire history of life only by the eruption of biological invention at the Cambrian Explosion. At the very least, it’s not a stretch to think we might be as important as penis worms.

“So I just think, here’s an example from the past when an ecological crisis happened because of ecosystem engineering,” said Darroch. “And we shouldn’t be too surprised or too staggered or too blown away by the fact that maybe it’s happening again. Biological organisms are an incredibly powerful geological force.”

The Cambrian Explosion—though it might have been devastating for the strange Ediacaran creatures that came before—was an unambiguously good thing for life on earth. It marked the official beginning of animals’ stewardship over a planet long immersed in “the boring billions.” Perhaps today the new technological world we have built for ourselves marks the beginning of a similarly epochal transition, and a new eon awaits that will appear as alien to us in 10 million years as the dizzying animal world of the Cambrian would have appeared to the pitiable creatures that came before. Or perhaps our shocks will prove less auspicious with humanity instead, leaving behind a ruined world—our legacy consisting only of a long environmental convalescence from civilizational excess.

As for the Cambrian period, its legacy was the tapestry of all animal life, which had unspooled from some forgotten ancestor. The planet was now an active one. Life crept and swam and spied on itself with eyes and chemoreceptors. Creatures killed one another and ate one another and hid in terror. Though we wouldn’t recognize it whatsoever, this was now our world—red in tooth and claw. After a 4-billion-year prologue that started in fire and ended in Snowball Earth, the pageant of animal life had begun, and the next half-billion years would be the most interesting by far.

The Cambrian Explosion might get all the credit for launching animal life on earth, but the ocean of the Cambrian period remained impoverished for millions of years as pulses of anoxic water intruded into the shallows, wiping out species after species in wave after wave of extinctions. This strange reta...