What the Wild Sea Can Be E-Book

Helen Scales

• Herausgeber: Grove Press UK
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 506

Veröffentlichungsjahr: 2024

Beschreibung

SHORTLISTED FOR THE WOMEN'S PRIZE FOR NON-FICTION LONGLISTED FOR THE BAILLIE GIFFORD PRIZE FOR NON-FICTION No matter where we live, 'we are all ocean people,' Helen Scales observes in her bracing yet hopeful exploration of the future of the ocean. Beginning with its fascinating deep history, Scales links past to present to show how prehistoric ocean ecology holds lessons for the ocean of today. In elegant, evocative prose, she takes us into the realms of animals that epitomize current increasingly challenging conditions, from emperor penguins to sharks and orcas. Yet despite these threats, many hopeful signs remain, in the form of highly protected reserves, the regeneration of seagrass meadows and giant kelp forests and efforts to protect coral reefs. Offering innovative ideas for protecting coastlines and cleaning the toxic seas, Scales insists we need more ethical and sustainable fisheries and must prevent the other existential threat of deep-sea mining. Inspiring us all to maintain a sense of awe and wonder at the majesty beneath the waves, she urges us to fight for the better future that still exists for the ocean.

Leseprobe

Also by Helen Scales

Around the Ocean in 80 Fish and Other Sea Life

The Brilliant Abyss

Eye of the Shoal

Octopuses

Eleven Explorations into Life on Earth

Spirals in Time

Poseidon’s Steed

Books for younger readers

Shells . . . and what they hide inside

Scientists in the Wild: Antarctica

Return of the Wild

Scientists in the Wild: Galápagos

What a Shell Can Tell

Great Barrier Reef

Dr Helen Scales is a marine biologist, acclaimed author and broadcaster who explores the wonders and plight of the oceans and the living planet. Her books, including The Brilliant Abyss and Spirals in Time, have been adapted for stage and screen, and translated into 15 languages. She writes for National Geographic Magazine and the Guardian, teaches at Cambridge University and is a storytelling ambassador for the Save Our Seas Foundation. Helen divides her time between Cambridge, England, and the wild Atlantic coast of France.

First published in the United States of America in 2024 by

Atlantic Monthly Press, an imprint of Grove Atlantic

First published in the United Kingdom in 2024 by Grove Press UK, an imprint of Grove Atlantic

This paperback edition published in the United Kingdom in 2025 by Grove Press UK, and imprint of Grove Atlantic

Copyright © Helen Scales, 2024

The moral right of Helen Scales to be identified as the author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act of 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of both the copyright owner and the above publisher of the book.

No part of this book may be used in any manner in the learning, training or development of generative artificial intelligence technologies (including but not limited to machine learning models and large language models (LLMs)), whether by data scraping, data mining or use in any way to create or form a part of data sets or in any other way.

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A CIP record for this book is available from the British Library.

E-book ISBN 978 1 80471 052 4

Grove Press UK

Ormond House

26–27 Boswell Street

London WC1N 3JZ

www.atlantic-books.co.uk

For Liam Drew and Emma Bryce,with gratitude for your friendship and forhelping me find words about wild things.

Contents

Prelude

PART ONE: OCEAN CONVERSION

Chapter 1: Ancient Seas

Chapter 2: Remixing Seas

PART TWO: VANISHING GLORIES

Chapter 3: Ice Walkers

Chapter 4: Missing Angels

Chapter 5: Poisoned Hunters

PART THREE: OCEAN REVIVAL

Chapter 6: Restoring Seas

Chapter 7: Rebalancing Seas

Chapter 8: Future Forests

Chapter 9: Future Reefs

Chapter 10: Living in the Future Ocean

Epilogue

Acknowledgments

Photo Credits

Additional Resources

Notes

Index

Prelude

First, they were bright white dots moving in the distance between sea and sky. Then, as I reached the end of the land at the cliff’s edge, the gannets were everywhere. From eyeline to the waterline almost two hundred metres below, huge birds filled all the available space. They followed invisible contours through the air in every direction and on every horizontal plane. Somehow, silently, they knew to steer to avoid each other, their black-tipped wings never touching. Those not in flight were sitting on every piece of cliff with room to land. They were lined up on ledges, one bird deep, and the flatter patches of scree were studded in nests, always spaced a sharp beak’s biting distance apart.

If someone told me this was all the gannets there are, every last one of them, coming to nest on these very cliffs, I might easily have believed it. But other colonies exist on both sides of the Atlantic, some even bigger than this one, and all of them in places where the surrounding ocean contains enough prolific life and food to sustain so many parents and hungry chicks. Gannets dive from great heights to hunt beneath the surface, folding their wings back and piercing the water with their arrowlike heads. Air sacs under their skin, like a subdermal cloak of bubble wrap, protect their bodies from the impact of thirty-metre dives. The ammoniacal tang of guano that wafted from the colony told me about the ocean’s immense productivity and all the fish they’ve been catching.

I came to the gannetry at Hermaness, the northernmost headland on the northernmost inhabited island in Scotland, because I wanted to see an outrageous amount of healthy ocean life. Gannets are the North Atlantic’s biggest seabirds, with metre-long bodies and close to a two-metre wingspan. They don’t have the vivid blue or red webbed feet of their tropical cousins the boobies, but they have their own understated elegance. Mostly white, the adults have a dusting of peachy-yellow feathers on their neck and head, a long, tapering beak, and striking pale-blue eyes ringed in cobalt—a gleaming swipe of eyeshadow, like Marilyn Monroe in an Andy Warhol print. I had only ever seen an occasional, solitary gannet, usually from afar, and had long wondered what it would be like to see more. When I found out that they gather in enormous colonies in the Shetland Islands, I decided to see for myself tens of thousands of these huge seabirds at once. I wanted to stare and soak up the awe of it all and remind myself that places like this still exist.

That day, July 18, 2022, when gannets lured me to the farthest end of the British Isles, became the day when my outlook on the world changed. It marked the beginning of the United Kingdom’s first “red” extreme heat warning. Two days of national emergency had been declared because of a heatwave so severe it put human lives at risk, and people were told their daily routines would have to change. Advice for the worst-hit areas, including my hometown of Cambridge, was to stay indoors, shut and cover windows, and generally slow down. During the hottest day in the United Kingdom on record, runways and roads melted. Train services were suspended. People lay awake throughout the warmest night ever, when temperatures didn’t fall below twenty-five degrees Celsius. And Britain wasn’t alone. Extreme heat was engulfing western Europe. Portugal was suffering from a worsening drought, and parts of France and Spain were ablaze with wildfires.

Meanwhile, at Hermaness, a thousand miles north of my home, it was mild and pleasant, but it was strange and unsettling to know that everywhere to the south was far hotter. Missing that heatwave, I think, made it even more disturbing as I tried to imagine what was going on at home. That day, everything felt different. Until that moment, the climate crisis had remained an alarming but still distant threat to me. Suddenly, I realised that the world I had grown up in had gone, that normality had changed and the climate crisis had arrived.

I had booked the trip months earlier and escaped the horrifying heat just by chance. But I also happened to arrive in the middle of another disaster that was hitting northern Scotland far worse than anywhere else.

Standing at the cliff at Hermaness, looking at the scene through binoculars, I watched pairs of gannets sitting together, shaking their long beaks from side to side, and others sitting quietly on their own, waiting for a partner to return from foraging at sea. And there, visible between the nests, were the dead bodies of so many other gannets. More corpses were piled at the base of steep sections of cliff, presumably the ones that fell off their nests.

Avian flu had killed them all. For the first time since the disease appeared in a goose farm in China in 1996, the virus had mutated into a highly contagious and virulent strain and was ripping through populations of wild seabirds. There had been isolated outbreaks of less deadly variants in the wild before, but nothing like this. The epicentre in early summer 2022 was Scotland—in particular, the Shetland Islands.

By the time I visited Hermaness, I had already encountered many dead gannets and other seabirds, several on every beach across the islands, in varying states of decay. Some were little more than feathers ground into the sand. Some were skeletons, archaeopteryx-like, head flung back, and wings outstretched. And some gannets just lay there, intact and perfect, staring blue eyes open, wings folded back as if they had deliberately dived from the sky and landed without a mark on their bodies. Only at the gannet colony were the dead mixed in with living birds. Depending on where I let my gaze rest, this was either a desolate view of ecological breakdown or a stunning scene of natural wonder.

Planet Earth is in the throes of extreme environmental change, a transformation in which the dominant driving force is humanity. In the Anthropocene, the human-dominated epoch in which we’re all living, many of the fastest, most dramatic changes are taking place in the ocean.

Within just the past fifty years, as people have been overexploiting species, destroying habitats, and releasing pollutants, the total mass of vertebrate life in the ocean has halved.* In that time, the ocean’s chances of being hit by lethal heatwaves, the kind that destroy kelp forests and coral reefs, have doubled. Every decade, the background noise levels in the ocean have also doubled, mirroring the growth in shipping, so that whales and other acoustic animals are having a harder time hearing each other. A plastic fog in the ocean is thickening and now comprises hundreds of trillions of particles. Since records began, the ocean has never been hotter. Sea levels are rising, and polar sea ice is shrinking. Seawater is becoming more acidic. Oxygen is ebbing away.

As humanity wades further into the Anthropocene ocean, changes are happening so quickly it can be hard to keep up with the streams of gloomy news. Scanning the science headlines, you might have come across recent news of a novel disease identified in seabirds caused by inflammation and scarring in their digestive tracts from the build-up of plastics that they swallow. Scientists have named this condition plasticosis. Or you might have caught word of how more marine species are being pushed towards extinction, with dugongs, abalone, and a type of Caribbean coral all recently added to the list of globally endangered species. Or that five out of the top ten commercially important fish populations in British seas are either overfished or depleted to critically low levels.

At the same time, people are making startling discoveries about what lives in the ocean and how this vast living system works. For instance, scientists recently discovered how northern elephant seals fall asleep while drifting down through the sea, like spiralling leaves, dreaming as they go, and sometimes take naps on the seabed. These enormous marine mammals breathe air, but they know they are in danger at the surface, where predators are more likely to attack, and so they only go to sleep underwater. Not long ago, another team of scientists tracked scalloped hammerhead sharks making regular dives into the twilight zone to search for prey and discovered that while they’re hundreds of metres down, they hold their breath. These water-breathing fish know to close their gills to avoid cooling their circulating blood in the frigid deep water.

A previously unknown seagrass meadow, full of species like seahorses, scallops, and cuttlefish, was discovered just off the British coast in St Austell Bay, Cornwall. And in the Bahamas, tiger sharks fitted out with cameras helped discover the world’s largest seagrass meadow, extending around ninety-two thousand square kilometres, more than twenty times bigger than the whole of Cornwall.* This finding alone increased the known global area of seagrass habitat by almost half.

I’m often asked by audience members at public talks or by interviewers during radio shows whether I am hopeful for the future of the ocean.† My common response is that it depends on which day you ask me and whether the last piece of news I heard or study I read was depressing or joyful. While I was watching the gannets of Hermaness, it dawned on me that I can hold both perspectives in my mind at once—my optimism and pessimism—and not let one push the other out.

There is no doubt that good and bad things are happening in the ocean, often pressed up tightly together, as the gannets showed me. Many discoveries that offer glorious and hopeful insights into ocean life are also tinged in trouble. In recent times, despite the growing threats of overfishing and warming seas, there are places where manta rays are flourishing; a population of at least a thousand of these magnificent, wide-winged cousins of sharks is swimming around in Komodo National Park in Indonesia; off the coast of Ecuador, a population was recently estimated to be the largest known in the world—by an order of magnitude—with more than twenty-two thousand mantas. And yet in both places, a portion of these animals show scars from collisions with boats and propellors, and many have been tangled in fishing nets or barbed with hooks.

Likewise, strands of hope run through even the most desolate ocean stories. Since I was in Shetland early in the avian flu outbreak, the situation has got far worse, and the virus has spread around the world. Millions of seabirds have died, the virus hitting more bird species in more locations than any previous outbreak. The virus has also jumped into wild mammals, killing foxes, otters, dolphins, and thousands of sea lions. Scientists are beginning to get a handle on how the virus is impacting wild populations, and in the thick of all the carnage, they have found a glimmer of resistance. The world’s largest colony of gannets is at Bass Rock in the Firth of Forth off the east coast of Scotland. This gannetry has suffered a huge die-off, but ornithologists have discovered some healthy-looking gannets with avian flu antibodies in their blood. Curiously, many of these survivors have jet-black eyes. It is not yet clear why this happens, or how the flu affects their vision, but for some reason when gannets fight off avian flu and survive, their pale-blue irises turn black.

In the messy midst of the changing ocean, so much has already been damaged and destroyed that discerning what the future may hold requires a careful balance of optimism and pessimism. A worse version of today’s ocean is not inevitable, but underestimating the scale of the problems and what needs doing to tackle them would be unwise. It is important to recognise that no place in the ocean is pristine and unspoiled anymore but also to appreciate that all is not lost; none of the ocean’s ecosystems and (almost) no species are entirely beyond hope. Many places in the ocean remain tremendously healthy and abundant, and there is still a great deal to fight for. This book, then, sets off with this mind-set on a journey through the Anthropocene ocean to find out what a better future could look like and what it might take to get there.

The starting point is the ocean’s distant past, which will root the stories that follow in the context of what happened over many millions of years, long before humans evolved. Keep that outlook in the back of your mind to help measure the changes unfolding in today’s ocean and grasp the magnitude of what is happening. For the centrepiece of each of the following chapters, I have picked living species and habitats that are responding in different ways to the Anthropocene. Many are familiar places and beloved animals, and I will dig deeper and uncover how their biology influences their chances of survival and dictates the course of action needed to help them thrive. We will meet species that are at the vanguard of a great modern remixing and conversion of the ocean, moving to new places and adapting to novel conditions, and that stand the greatest chances of surviving by themselves. We will also encounter a suite of species whose glory is already fading fast, the ones that will be the hardest to save and will require the most urgent action. These animals are frantically imperilled by the biggest threats to ocean life and could be the first to succumb in turn to heating seas, overfishing, and pollution. Among them are the polar animals that are disastrously sensitive to rising temperatures and cannot persist without the coldest, frozen seas; the species that grow sedately and to such grand old ages that their exploited populations cannot keep up and replace themselves fast enough; and the apex predators that balance precariously at the top of food chains, where their bodies soak up toxins from the contaminated seas. Together they pose a great challenge but not a hopeless one, of how to reverse their bad fortunes, and they serve as a warning of worse problems that need to be avoided elsewhere in the world.

Ocean wildlife has a tremendous capacity to regenerate and recover from dreadful losses and depletion. Often all that is needed is for the exploitation, destruction, and pollution to stop—a great deal of optimism about the ocean comes from this possibility. Even what seemed to be irredeemable catastrophes have been turned around, including some involving high-priced luxury fish and neglected areas of seabed.

Sometimes the recovery process needs a helping hand to kick-start natural cycles and restore balance. And some habitats face such big problems they will likely require far more deliberate steering and coaxing through the vicissitudes of the Anthropocene ocean. Scientists and conservationists are already working to engineer future-proof species and habitats that can withstand the continuing changes. Their ambitions generally are not to return the ocean to the way it was before humanity began inflicting so many troubles but rather to reach towards a resilient version of the ocean that is still healthy and abundant and, in key ways, different and new—not a rewinding that could ultimately fail but a rewilding that will last.

Together, ocean dwellers and their habitats have a lot to tell us about how the Anthropocene ocean is run through with inequalities. By no means is everything and everyone in the same boat. It is clear that some habitats and wild species—and people too—are already shaping up to be winners and some to be losers in the changing ocean. A critical part of a better future will be to find ways to undo inequalities and build an ocean that is just and fair and that benefits as many people and the greatest portion of nature as possible.

The future of the ocean matters to everyone. No matter where you live and what you do, even if you have never seen the sea in real life, you would not exist—none of us would—without the ocean. When astronomers examine other planets for signs of life, the key feature they search for is liquid water. Here on Earth, the ocean is where life began billions of years ago, and it is what has kept the planet alive ever since. Seawater covers seven-tenths of the planetary surface and plunges to many miles deep, and in its enormity absorbs huge amounts of heat beating down from the sun. Restless ocean currents swirl heat around the globe, preventing the tropics from scorching and supporting the mild mid-latitudes where many people live. The ocean is a rainmaker, providing most of the water that evaporates and falls on land. It generates weather systems and influences the climate we all experience in our daily lives.

The ocean makes the earth habitable not just by the physical presence of water but by the presence of life itself. Half the oxygen we breathe is made by multitudes of minute sun-fixing organisms, the phytoplankton that float through the seas. Phytoplankton also play their part in regulating the climate. They make clouds, which reflect the sun’s heat, by releasing particles into the atmosphere that cause water vapour to condense into droplets. Ocean life also mitigates the climate crisis by removing at least a quarter of humanity’s carbon emissions from the atmosphere. Phytoplankton absorb carbon dioxide and, when they die, create flurries of organic particles, called marine snow, which settle into the deep. A myriad of other life forms are critical in this drawdown of carbon, from underwater forests and meadows to giant whales and their plankton-fertilising faeces, and the trillions of glittering fish, called myctophids, that migrate each day between the sea surface and the shadowy twilight zone a thousand metres down.

The species and habitats discussed in this book are all vital parts of this life-giving system. They are sentinels of the rapid changes already underway in the Anthropocene ocean, and they forewarn of greater changes to come. In the coming pages, I will focus on what could happen in the next few years and decades, with the end of the century out there on the horizon. I picked this timeframe for a few reasons. On a practical level, 2100 is commonly the date at which scientific models and predictions aim, and so there are many studies that consider what the ocean will be like by then. We will all experience changes unfolding in the next years and decades, as will many of the people we know and care about. And if you think 2100 feels far off, remember that many children born today should still be alive to see the turn of the twenty-second century.

Crucially, the next few years are when decisions made will determine—one way or another—how the next phase of the Anthropocene ocean plays out for a considerable stretch of time to come. Right now, there are choices to be made, but the window of opportunity to meaningfully act is closing. Soon the ocean will reach a point when it heads down a certain path, and it will become harder and harder to change course.

Experts predict that carbon emissions must peak by 2025, at the latest, followed by sharp global reductions, if there is to be any chance of keeping global heating to within 1.5 degrees Celsius and avoiding the worst-case scenarios for people and the planet. While that target is looking less likely as the present decade wears on and emissions keep climbing, the Intergovernmental Panel on Climate Change (IPCC) has laid out a road map for how those emissions reductions could happen, underscoring the fact that the necessary technologies and solutions already exist. The most promising options are solar and wind energy, as well as preserving intact forests and other carbon-rich habitats, including in the seas.

Exploring the future of the ocean demands a fair amount of mental time travel, both backwards and forwards. The trick to navigating these waters will be to keep a sense of perspective (the ocean has always changed), to not go it alone (share these stories and ideas, talk about them so more people will know what is happening), and to make sure along the way to keep seeing the glory and feeling wonderment in the ocean. I hope this book will offer an antidote to the rising tide of eco-anxiety and fears for the future of the planet. Turn that fear into commitment and initiative. What matters most now is to not look away in anguish but to confront the problems and to know how bad things are and understand why they got this way, while at the same time wanting and hoping for the future ocean to be better.

*The 2015 Living Blue Planet Report, by the conservation organisation WWF, compiled data on the 5,829 populations of 1,234 mammal, bird, fish, and reptile species that live in the ocean, and found that between 1970 and 2012 their numbers had declined by 49 per cent.

*All these discoveries, from snoozing elephant seals to giant seagrass meadows, were made within roughly a half year, in late 2022 and early 2023.

†I am asked this almost as often as that other excellent question, “What is your favourite sea creature?”

PART ONE

OCEAN CONVERSION

Chapter 1

Ancient Seas

In a desk drawer, among all sorts of things I’m saving, is a small witness to the changing ocean. The thumb-size piece of slate is etched with narrow silver lines that are smooth along one edge and serrated on the other. I found it at the base of a crumbling cliff that was folded and twisted by an aeon of orogeny. The marks look like the script of some long-lost language pencilled on the rock. In fact, these are fossils of animals that lived 430 million years ago, or thereabouts, and I like them especially for the name they’ve been given: graptolites—from ancient Greek words graptos, meaning “marked with letters,” and lithos, meaning “stone.”

The impressions graptolites left behind hold messages that took palaeontologists a long time to decipher. Many assumed these markings were fossilised plants. Others realised they were animals but had differing views on which kind, variously labelling them as corals, hydroids, or the mossy-looking creatures known as bryozoans. Ultimately the matter was settled, and it was agreed that graptolites belong among an obscure group of ocean dwellers called pterobranchs. Each sawtooth line on my stone was once a colony of tiny animals. They lived together inside a house of interconnected tubes, which they actively built around themselves, like a spider making its web. Their homes were the only parts of graptolites that fossilised, but these are enough to tell us what their colonies looked like and what kind of lives they led. Early on in their evolution, graptolites grew on the seabed, fixed to boulders or rooted in mud. Then in time, some varieties floated away and were among the first animals to become plankton. These abundant drifters colonised open seas all around the world and swiftly evolved into flurries of different-shaped species. Some graptolites were Y-shaped, some poker-straight or two-pronged like a tuning fork, and some grew into spirals that twirled up and down as they sifted floating microbes from the water.

Now, though, the open ocean is empty of graptolites. The last of the planktonic species went extinct around three hundred million years ago. That seemed to be the end of them all, until recently, when a group of tiny animals, the Rhabdopleurida, were deemed to be living graptolites. It wasn’t a new finding but a new interpretation of animals that scientists already knew about, microscopic, seafloor-bound colonies, which live all through the ocean, from polar seas to the tropics, from coastlines to a half mile down, and are the colour and translucence of amber. Only five living species have been found, a fragmentary recollection of the once-ubiquitous graptolites, the ghosts of a vanished world.

While contemplating the future of the ocean, it’s worth pausing to turn around and look back. The ocean’s backstory matters because it provides context for what’s happening now. It lets us see what the ocean has been like and how it changed in a prehuman world. Long before us, great tides of ocean dynasties have risen and fallen, and the seas have been both a cradle of evolution and an arena for extinction. Looking back offers a chance to compare humanity against other planetary life-shaping forces. We can search for clues as to what changes lie ahead, note the warnings against misleading assumptions, and seek solace in the fact that, one way or another, life in the ocean goes on.

To think about the past requires an obvious and dizzying shift in perspective, because ocean life stretches behind us for more time than our human brains can instinctively grasp. We must briefly let go of our customary horizons of hours and days, years and decades, centuries and, at a stretch, millennia. Think instead like palaeontologists, who have learned to find ancient moments trapped in stone, then to gather them up and piece together stories that take millions of years to be told. While we try not to get overwhelmed by the scale and intricacy of it all, we can pick out details that tell a wider story of the changing ocean. From there we can begin to sense the rhythm and pace of ocean life.

Trilobites look oddly familiar, as if a woodlouse scuttled under a rock and then emerged on the other side much larger, more ornate, and more than a half billion years older. Were I a more skilled and patient fossil hunter, I might find trilobites lodged in rocks not far from my graptolite-embossed slate. There are fossil trilobites on continents across the world. These animals existed in the earliest of three great chapters of complex life on earth—the Palaeozoic, meaning “ancient life,” which was followed by the Mesozoic (“middle life”) and then the Cenozoic (“new life”). Trilobites in the Palaeozoic weren’t the first large animals to evolve, but they were undoubtedly trailblazers. They worried Charles Darwin because they seemed to confound his theory of gradual evolution via natural selection. Trilobites emerged far too quickly, too completely, and too long ago to fit his theory, as perfect creatures pressed into stone.

Trilobites evolved shortly after a three-billion-year prelude in which the only living things were single-celled microbes colonising the ocean, followed in the fullness of time by enigmatic wisps of simple, mostly jelly-based creatures that palaeontologists are still trying to make sense of. Then the Palaeozoic era opened with a dramatic twist in the history of life on earth. This era is divided into six periods; the first was the Cambrian, when evolution suddenly accelerated and ran at full tilt, churning out a mob of animals, including many that looked wildly different to anything alive today, from nozzle-nosed predators to luxuriantly spiky worms. The trigger for this flurry of life, known as the Cambrian explosion, is still a matter of debate. It may have had something to do with the fact that, for a long time leading up to it, the whole planet was frozen. As snowball Earth thawed, likely due to volcanoes spewing planet-heating carbon dioxide, the climate became more favourable for life to flourish. Rocks on land, as yet devoid of living things, began to erode and release nutrients into the ocean that organisms used to grow and build their skeletons, including enormous numbers of trilobites.

Darwin needn’t have agonised over trilobites. It was partly a matter of timing. He was quite right when he surmised that ancient seas must surely have been swarming with life, though in his day nobody had yet found any evidence for it. When Darwin was writing and thinking about evolution, most of the world’s oldest animal fossils remained unfound underground, including the extraordinary variety of Cambrian life in the Burgess Shale in Canada’s Rocky Mountains, which wasn’t uncovered until after his death.

A recent study of trilobite fossils has shed light on the timing of the Cambrian explosion and strengthened the idea that evolution can run at different speeds and has sometimes been breathtakingly fast (geologically speaking). A team based at the Natural History Museum in London used a large new collection of Cambrian trilobites to track how their appearance changed over time. The fossils went through an early, short burst of frantic innovation, showing that the Cambrian explosion may have truly gone off with a bang, lasting a brief twenty million years. Once the explosion died down, the rate of evolution among the trilobites levelled off and ticked steadily along.

By the Ordovician, the Palaeozoic period after the Cambrian, the ocean was brimming with trilobites. They ranged from flea-size swimmers to shovel-shaped diggers seventy centimetres long, although most species were neatly pocket-size, measuring between three and ten centimetres. Their basic anatomy was a head, thorax, and tail, with a ridged shell divided lengthwise into three sections, hence the name trilobite, and multiple pairs of legs underneath, like a centipede. These simple creatures were moulded and embellished into a phenomenal variety of forms. Many trilobites sprouted impressive spines and barbs, elegant quills, and devil horns. Some were smooth and rounded, like Bumastus, which looked just like an armadillo if you popped off its head and hid its tail. And like armadillos and woodlice, most trilobites could curl up into a ball when they were scared.

From their fossilised remains, it’s possible to interpret the ways many trilobites lived their lives. Masses of them scurried across the seabed, leaving footprints as if they had walked over wet cement; these imprints were preserved by rapid burial in sediment and then slowly turned into stone. Fossil trails captured the details of a hunting foray: a line of worm tracks joined by those of a trilobite, and then the trilobite walking off by itself, worm presumably in belly. Cryptolithus evolved to be filter-feeding trilobites that stirred up the sediment by scrabbling the seabed with their forelegs, then straining suspended food particles through their perforated, colander-like heads. Others never set a foot down but chased after prey through the water, aided by hydrodynamic shells. Chunks bitten out of their shells show that trilobites were prey for other animals, such as the giant sea scorpions that also roamed the Palaeozoic seas. Planktonic trilobites floated in great midwater swarms, occupying a pelagic niche similar to the one that krill occupy today. In shallow tropical seas, trilobites were beetling around the world’s first true coral reefs, which had been built in the Ordovician by horn- and honeycomb-shaped corals. Some trilobites ventured between the tides and foraged on exposed tidal flats, but it seemed they never moved into rivers or lakes or made a permanent move onto land.

Uniquely among animals, trilobites’ eyes were made from crystals of the hard mineral calcite, which means they were often exquisitely preserved, and their shapes and arrangements tell us even more about these creatures’ lives. From their inception, Cambrian trilobites had complex, multifaceted eyes, similar in general form to the compound eyes of living insects and crustaceans. Some had eyes on long stalks, which scanned for prey while their bodies lay hidden in the mud. Erbenochile trilobites had columnar eyes that gave them almost 360-degree vision, each eye with a small, overhanging brow that shaded it in bright light. In deep waters of the twilight zone, where sunlight is dim, Cyclopyge trilobites soaked up rare photons with enormous eyes that occupied much of their heads, like the helmet eyes of dragonflies. Deeper still, trilobites evolved to be eyeless and blind, vision serving no purpose in the dark midnight zone.

Some trilobites resembled their nearest living relatives, the horseshoe crabs. Olenellus had a rounded, helmetlike head, rearward-pointing body spines, and a long prong for a tail. Not in fact crustaceans, the trilobites and horseshoe crabs are more closely aligned with spiders.

In all, more than twenty-five thousand species of trilobites are known, and more are constantly being found. (For comparison, there are roughly one thousand named dinosaurs.) They were fossilised in the millions, thanks in part to their tough exoskeletons. Trilobites periodically moulted their outer layer, growing new, bigger ones and tossing the casts into the fossil record, duplicating themselves and increasing the chances of being remembered through the passage of time.

The enormous diversity of species and ecology of trilobites show what very early ocean ecosystems were like, with habitats and food webs that are broadly recognisable in the contemporary ocean. More than five hundred million years ago, although the shape of the global ocean was very different, ocean ecology was already working, in many similar ways, as it does today.

Being so prolific and dotted around the planet, trilobites have also helped scientists reconstruct what the entire global ocean used to look like. For much of the Palaeozoic, the Northern Hemisphere was covered in the huge Panthalassic (meaning “all-sea”) Ocean, and the continents were located mostly in the Southern Hemisphere. The world was warm, with little ice locking up water, and many of the continents were flooded in shallow seas, each home to a unique assortment of trilobites that didn’t cross the deeper ocean in between. Later, when they were long dead and rockbound, fossil trilobites travelled around the planet, pushed by the forces of tectonic drift. Mapping the range of trilobites across modern-day continents is one way palaeontologists have worked out how landmasses moved and the ocean reshaped around them. Through much of the Palaeozoic, a supercontinent, Gondwana, was made up of many of today’s continents and subcontinents all clustered together, including Australia, Antarctica, Africa, India, and Madagascar. Today, their shared trilobite fauna is testament to that earlier convergence. For instance, the same tropical species of trilobites have been chipped out of rocks in western Newfoundland, in New York State, and in the Inner Hebrides archipelago in Scotland, showing these lands were all once part of the same ancient continent.

The stories of trilobites have much to tell us about what the ocean used to be like, and together they refute a wider misconception about evolution. Trilobites are proof that life has not simply been advancing from primitive towards ever more advanced forms. They show that since early times, some organisms have been remarkably specialised and sophisticated. And perhaps the most important message from the trilobites is that their early abundance and diversity weren’t enough to protect them from the changing ocean. Look all through the seas today, and not a single living trilobite is to be found.

After almost three hundred million years of scurrying and swimming, drifting, digging, and rolling up in balls, trilobites went extinct. They were among the species wiped out by the catastrophic Permian extinction event, which drew the Palaeozoic era to a close. This was the most devastating of the five ancient mass extinctions.* The cause was likely a spell of runaway global warming, triggered by immense volcanic eruptions, which filled the atmosphere with so much carbon dioxide the ocean was cooked, acidified, and sapped of oxygen until most aquatic life suffocated. That was the end of the trilobites, although in fact they had been in decline for much longer.

Trilobite diversity peaked in the late Cambrian and into the early Ordovician, and thereafter this group’s splendour had been fading away. For the rest of the Palaeozoic—through the Silurian, Devonian, Carboniferous, and finally Permian periods—trilobites had been relinquishing their dominance in the ocean. Steadily, their diversity diminished until a single family remained, containing a handful of species that were quite plain and small compared to their predecessors.

We have some clarity as to why trilobites were knocked back. For instance, at the end of the Ordovician, the supercontinent Gondwana drifted over the South Pole and became covered in giant ice sheets, pushing the earth deep into an ice age. Sea levels dropped, and when continental seas dried out, crowds of tropical trilobites lost their habitat and went extinct. Those species that happened to be better able to cope with the cold survived. What continues to mystify is why trilobites didn’t rebound once the ice age was over and conditions on the earth became more agreeable. New trilobite species were still evolving but not fast enough to replace the older species that were going extinct. No doubt the ocean filling up with new predators had an effect, including the first fish and squid, which were busy chasing after trilobites. Another suggestion is that trilobites weren’t very good at shedding their exoskeletons. Fossils show that many injured themselves trying to climb out of their old shells, emerging with damaged eyes and misshapen heads.

Nobody has yet found a convincing, single explanation for the trilobites’ long-term demise, which suggests it was likely a mix of changes and challenges emerging in their world. Whatever the ultimate causes were, from the end of the Ordovician onwards, trilobites suffered repeated setbacks from which they never fully recovered. Their former success did not predict their future survival.

The second great chapter in prehistoric life, the Mesozoic era, got underway around 250 million years ago in the aftermath of the mass extinction that devastated the earth’s biosphere. Trilobites were gone. Huge coral and sponge reefs were gone. So were sea scorpions and spiny sharks called acanthodians. Many other groups of organisms, while not entirely lost, were stripped back to a tiny portion of their former diversity and abundance. In all, fewer than one in ten species survived. For millions of years after the extinction, a disaster fauna, as palaeontologists refer to it, existed on the seabed, made up of species that were just holding on and by no means thriving. The situation was better up in the open water, where shoals of conodonts—eel-like, five-centimetre-long fish with bulging eyes and no jaws—proliferated. There were also spiral-shelled cephalopods called ammonoids, which looked similar to living chambered nautiluses, as well as an increasing diversity of bony fishes. These animals all became prey for a group of animals whose ancestors had left the ocean more than a hundred million years earlier and in the Mesozoic made a spectacular return to the sea.

Back in the Palaeozoic, a group of fishes had gradually adapted to life beyond the tideline. They already had four legs, which they used while still living at the shallow edges of the sea, and some of them walked out onto land and became the ancestors of all the land-living vertebrates alive today: the amphibians, reptiles, birds, and mammals. Collectively, these vertebrates are known as tetrapods, even the ones that later turned some of their four legs into wings or flippers—and reptiles did both.

By the time the Mesozoic was underway, the reptiles known as dinosaurs* were famously ruling the land, and pterosaurs had taken to the skies. Meanwhile, the ocean was dominated by different groups of reptiles. Having lost their ancestral fishy gills, these animals drew gulps of air into their lungs and then leapt, slithered, and strutted back into the sea and very soon were well acclimatised to their revamped aquatic life. Within a few million years of the end-Permian mass extinction, reptilian apex predators were swimming through all the seas and making a major impression on the rest of ocean life.

These were the real-life embodiment of mythical sea monsters, with all the ferocity and grandeur we might imagine. Cruising around were twenty metre-long ichthyosaurs, some as long as twenty-six metres. They looked like blue whales with elongate, tooth-filled jaws. Other ichthyosaurs were roughly the size and proportions of bottlenose dolphins. Excalibosaurus had a rapier-like rostrum, as swordfish do today, and presumably used it in a similar way to slash through shoals of fish. Tylosaurs looked like enormous modern-day orcas, up to twice their size, and may have hunted like them too, subduing prey by ramming into it with their bony snouts and then tearing it apart with razor-sharp teeth.

Plesiosaurs looked like archetypal incarnations of the Loch Ness monster, with a streamlined body, tiny head, and two pairs of long flippers, which they paddled in elegant undulations to fly underwater. Many had phenomenally long necks, some measuring more than six metres and taking up two-thirds of their body length. It’s tempting to imagine plesiosaurs using their necks to strike out at prey, like a coiled snake, or to grab pterosaurs flying above the waterline. In fact, the plesiosaurs’ abundant neck vertebrae were likely quite stiff and didn’t flex from side to side. These reptiles may have floated horizontally in the water, dipping their necks below their body to rake fish shoals with a snarl of intermeshed teeth or to root out prey in the seabed.

Swimming through Mesozoic seas were reptiles that looked like monitor lizards, others like giant newts, salamanders, or crocodiles, and huge, long sea snakes with little legs and gently bulging bellies. This was also the era when another group of reptiles, the sea turtles, first evolved, including the biggest ever to exist, the two-ton Archelon, which grew close to five metres long and would have needed four king-size mattresses to stretch out on.

In all, reptiles retraced their ancestral past and took to the ocean on at least a dozen separate occasions. No one knows for sure what drew them all down to the sea—one idea is that the land was getting crowded with other animals while the ocean offered plenty of space and prey—but clearly reptiles learnt to swim many times over. Their bodies underwent extreme adaptations to enable them to live underwater. Fossils of ichthyosaurs show that their arms gradually became shorter and their hands longer with more fingers—all the better to act as large, swimming flippers. Some ichthyosaurs evolved eyes the size of ten-pin bowling balls, bigger than those of any other animal extinct or alive, which gave them excellent vision as they hunted in the dim waters of the twilight zone. Thalassodraco (“sea dragon” in Greek) looked like a dolphin with a huge ribcage, accommodating enormous lungs that let it take great breaths and stay longer underwater.

Occasional food remains preserved in their stomachs and the arrangement and shapes of their teeth tell us Mesozoic marine reptiles had a varied animal-based diet. The most terrifying of all were those that filled an ecological niche that until then had been empty. Hyper-carnivores—predators that eat other predators—hadn’t existed until the Mesozoic. It’s evident that swimming reptiles were in the habit of eating one another. A fossilised Diandongosaurus, a close relative of plesiosaurs, has been found with its hind left flipper missing, likely bitten clean off by a fellow reptilian predator. And a five-metre ichthyosaur swallowed most of a four-metre thalattosaur, another Mesozoic reptile, shortly before it died, as palaeontologists saw when they found a fossil within a fossil.

Not all the swimming reptiles were spine-chilling carnivores. The oldest known plant-eating marine reptile, Atopodentatus, had a strange hammerhead skull and may have had an unusual two-step mode of feeding. With its chisel-shaped teeth, it likely scraped at seaweeds on the seabed. It also had a row of needlelike teeth, which formed a mesh and could have sieved fragments stirred into the water column.

And not all these swimming reptiles were giants. Many of the early ichthyosaurs were salmon-sized, including one called Cartorhynchus, which had a stubby snout, pebble-shaped teeth for crunching snails and clams, and big flippers with flexible wrists that would have let it move about on land. In life it would have looked rather like a small seal that basked on the shore and dived in the water to feed.

Throughout the 190-million-year span of the Mesozoic, an ebb and flow of marine reptiles occurred, as some went extinct and new forms kept evolving. To begin with, they mostly stayed near the shorelines fringing the coasts of the supercontinent Pangaea, which had formed when other continents collided with Gondwana and spanned both hemispheres. Then, as Pangaea began to break apart, the continents and oceans we know today began taking shape. Volatile seams in the earth’s crust opened, and the new Pacific and Atlantic Oceans were born. Marine reptiles swam along the seaways that opened up between continents and soon were living all across the global ocean.

The Mesozoic was more than just an exciting time for its assortment of swimming reptiles. The reign of sea dragons was part of an oceanic revolution that shaped much of life on earth in ways that continue into the present day. The procession of predators triggered an evolutionary arms race as their prey found means of survival and escape, which in turn caused new life forms and lifestyles to flourish.

A major battleground was the seabed, where reptiles as well as bony fishes, sharks, ammonoids, and crabs were all busy searching for shelled creatures and crushing them in their powerful jaws or claws. The prey responded in many different ways. Clam-like bivalves began a long game of hide-and-seek that still goes on today, as they escaped downwards, burrowing into the seafloor and sprouting long breathing tubes.* Sea lilies, umbrella-shaped relatives of starfish, escaped the feeding frenzy by drifting off into open waters. Snails evolved thicker, spinier shells; some also took flight from the dangerous seabed, evolving tiny wings and flitting off into the plankton as sea butterflies. Other snails fled the oceans altogether. The Mesozoic reptiles that went back to the sea and evolved into terrifying sea monsters were part of the forces that drove snails into fresh water and ultimately onto land.

Predators evolved countermeasures to keep up with their prey. They developed excellent vision and camouflage, improving their chances of spotting prey from further away and sneaking up undetected. And predators evolved new ways of breaking through tough-shelled defences. If you ever find a seashell with a neat, round hole, it contained a creature that was killed and eaten via a mode of attack that first evolved in the Mesozoic, when predatory snails gained the ability to drill through the shells of other molluscs and suck out their soft insides.

Ocean food webs had become a scramble of animals eating and getting eaten. In 1977, mollusc expert Geerat Vermeij proposed this ferocious struggle should be called the Mesozoic marine revolution. Since then, signs of the revolution’s effects have been noted in many other animals, but only in 2021 did this transition come into view across the entire fossil record. Earlier fossil studies found obvious signs of the five prehistoric mass extinctions—it’s not too difficult to spot the annihilation of more than 90 per cent of all life. But the influence of mounting predation in the Mesozoic was more gradual and didn’t clearly show up. With advances in computing power and new ways of analysing enormous fossil data sets, researchers can now extract patterns that were previously hidden from human eyes and minds. Scientists at Umeå University in Sweden built what amounts to an interactive digital map of the entirety of ancient ocean life through space and time. It shows that the Mesozoic marine revolution was indeed a life-shaping force equally as powerful as mass extinctions. Dramatic global catastrophes have caused ocean-wide changes in biodiversity, and so too did the prolonged shift that took place under the influence of marine reptiles and all the other predators roaming through Mesozoic seas.

Today the only reptiles that live a fully oceanic life are sea turtles and sea snakes. All the other fish-like, whale-like, and lizard-like Mesozoic lineages went extinct. The last of the ichthyosaurs were gone by around one hundred million years ago, likely because they weren’t evolving quickly enough to adapt to an intense period of climate change. Meanwhile, the plesiosaurs made it to the end of the Mesozoic, then died along with three-quarters of life on earth, extinguished by another mass extinction. That moment, sixty-six million years ago, is the most infamous planetary disaster, one that captures people’s imaginations more than any other and shapes the popular view of extinction. An asteroid hit the earth, the skies darkened, and the dinosaurs’ days were numbered. A story often told is that once dinosaurs were out of the way, mammals had their chance to arise from their shadows. It’s a dusty old theory, challenged by many lines of evidence in the fossil record. And yet, the idea persists that mass extinctions pave the way for new life to rebound—that devastation is a prerequisite for renewal.

Machine learning tools are helping scientists construct another powerful new view of biodiversity through time. By programming computers with artificial intelligence algorithms, biologist Jennifer Cuthill from Essex University and colleagues have held millions of fossils in their virtual hands and tracked subtle shifts in life from the Cambrian to the present day. Their method detected the same five mass extinctions that everyone else has found, plus seven other major extinction events. They also pinpointed seventeen times in the past when life flourished and evolution surged into action, which they called mass radiations. Critically, they found that mass extinctions and mass radiations don’t tend to pair up in the fossil record. There are only two examples of a notable extinction followed right away by a great radiation. On fifteen other occasions, radiations happened nowhere near an extinction event. Rather, they were often associated with evolutionary innovations, such as the development of eyes or the movement of different forms of life onto land. There is little evidence that mass extinctions are a force of creative destruction.

The pace and rhythm of evolution in deep time is not simply driven by dramatic extinctions; life is far more responsive and complex. A catastrophe isn’t needed to steer evolution down new avenues and sculpt biodiversity in novel ways. A tangle of other elements is constantly in play, as more gradual and less immediately lethal environmental changes take place. And these intricate responses are evident in the ways ocean life changed through the third great chapter of life, the Cenozoic,* beginning sixty-six million years ago and leading up to now.

When the aftermath of the dinosaur-killing extinction had subsided, roughly ten million years into the Cenozoic, the earth was in the grip of fearsome global warming. There was no ice at the poles. Forests flourished in Antarctica. Flying lemurs leapt through the trees on Ellesmere Island in far northern Canada. The situation suddenly escalated fifty-six million years ago, when the deep sea released a colossal burp of the potent greenhouse gas methane, perhaps because gradual heating had caused seabed sediments to destabilise. Global temperatures spiked by ten degrees Celsius in the ocean surface and five degrees Celsius in the deep sea. The ocean became more acidic, a mass extinction swept through deep-sea ecosystems, species moved towards the poles, and the earth became a tropical hothouse.

Many scientists consider this to be the closest analogue to anthropogenic climate change, and while certainly the most recent such event, it wasn’t as extreme as what’s happening now. In comparison, changes in ocean chemistry and the rate of carbon release are an order of magnitude higher today because of humankind. Back then, temperatures continued to rise until forty-nine million years ago, when the climate dramatically changed course. Carbon dioxide levels in the atmosphere began to fall, thanks in part to the chemical weathering of continental rocks,* which accelerated when India collided with Asia, building the Himalayan mountain range. Temperatures steadily dropped, and the earth, recovering from its fever, began to descend into an ice house, setting the scene for the climate we live in now.

The world was also beginning to look much like it does now. The continents had drifted into their approximate current locations, except for some subtle but important tectonic shifts that were still to come. Around thirty-four million years ago, the southern tip of South America pulled away and left Antarctica on its own. This allowed an oceanic current to begin swirling endless clockwise loops around the continent, effectively isolating it from warmer waters in the rest of the ocean. It also happened that the Antarctic continent had come to sit right over the South Pole, putting it in the perfect place to get very cold very fast, and it was soon covered in a giant sheet of ice.

Not until much more recently, around 2.7 million years ago, did the seas at the North Pole begin to turn to ice. The story of how this happened is more complex and disputed than Antarctica’s deep freeze. But likewise, continental movements were involved. The gap was gradually closing between North and South America. Where the Central American Seaway had provided a direct connection between the Pacific and Atlantic, now the land bridge of Panama lay in the way, preventing the two oceans from directly mixing. This had profound effects on global ocean circulation and climate, including intensifying the Gulf Stream, which flows from the Caribbean Sea into the northeast Atlantic. The closure was also linked with the strengthening of the global conveyor belt, the ocean circulation that flows around the whole planet today. By pushing moisture-laden air northwards, the Gulf Stream likely played a part in boosting snowfall over Greenland and North America, increasing the size of glaciers that were forming in the Northern Hemisphere as the earth entered a prolonged and volatile ice age.

In the Cenozoic, the ocean settled into its present-day configuration and welcomed the arrival of many life forms that still prevail. A recurring theme during this era was the return of tetrapods to the ocean. Yet again, four-footed land animals gave in to the irresistible lure of the sea, many times over. The main protagonists this time weren’t reptiles, as in the Mesozoic. Instead, it was the turn of mammals to go back to their aquatic roots. Seven different types of mammals dipped their hooves, paws, and feet in the water and evolved ways to survive at sea, in time becoming integral parts of ocean ecosystems.

Around fifty million years ago, an assortment of prehistoric mammals walked the shores of the Tethys Ocean, an ancient water body that used to connect the Atlantic and Indian Oceans across northern Africa. Among them were animals that trotted on long, thin legs and had something of the wolf in them. These were archaeocetes, the beginning of a long animal dynasty that led up to modern cetaceans—the whales and dolphins. They were animals with even-toed hooves, a group that today includes giraffes, camels, antelopes, llamas, sheep, pigs, and cows. Modern cetaceans’ closest living relatives are hippopotamuses.

Proto-whales went through a series of evolutionary stages, as shown by elegant fossils, at first amphibious then increasingly oceanic. They followed parallel lines of evolution leading them to resemble many of the giant marine reptiles that swam before them. Their legs turned into flippers, and their tails sprouted powerful, wide flukes, although they didn’t swing sideways, like the tails of swimming reptiles, but up and down, a throwback to the gait of their terrestrial forebears; contrast a reptilian gecko, which sashays along flexing its spine from side to side, with a cheetah, which bends its back up and down as it runs. It took roughly ten million years for whales to become fully pelagic, with nostrils on the tops of their heads (i.e., blowholes) and inner ear bones adapted to hearing well underwater. But the cetacean lineage really took off a while later.

A key point in the evolution of whales was when Antarctica broke away from South America, and the global climate shifted into an ice house. This was when the two main cetacean lineages—the baleen whales (mysticetes) and the toothed whales (odontocetes)— diverged from each other. With Antarctica on its own, a current now whirled around the continent, which not only sent temperatures falling but also triggered deep mixing of the Southern Ocean, stirring nutrients into upper layers of the sea. Consequently, oceanic ecosystems around the world became enormously productive. Plankton proliferated, and the new group of filter-feeding whales with hairy baleen plates in their mouths had plenty to eat. Around that time, toothed whales began to interrogate the ocean with beams of sound, hunting for prey with their new echolocating powers. From these early odontocetes, a lineage of smaller cetaceans separated and began filling seas and rivers with dolphins, porpoises, narwhals, and orcas.*

At the time when the proto-whales were starting to wade and swim, a different group of mammals were splashing along the shores of the Tethys Ocean. Sea cows began as pig-size relatives of elephants with stumpy legs that walked on land and wallowed in the shallows. Also known as sirenians, they spread across the planet and evolved into assorted species of dugongs and manatees, which mostly lived along warm and tropical coasts and spent their days chewing on seagrasses. Some moved into the North Pacific rim and fed on the giant kelp forests that started growing there around thirty million years ago as the ocean was cooling. They shared their kelp forest home with yet another gang of aquatic mammals—desmostylians, stocky, hippo-size animals with two pairs of short, goofy tusks sticking out of their mouths. Like many other herbivorous marine mammals, they had thick, heavy bones that acted as ballast to help them sink while they foraged underwater, especially important when their rotund bellies filled up with digestive gases produced by their plant-based diet. Desmostylians existed for only a narrow window