Strange and wondrous creatures: plankton and the origins of life on Earth
When I arrived at Wickford Harbor in North Kingstown, Rhode Island, early one June morning, the sea was moderately calm, with a distinct metallic sheen, like a wrinkled sheet of foil someone had tried to rub smooth. Vitul Agarwal, a young oceanographer, waved to me from beside a research trawler with the name Cap’n Bert-painted on its hull. Dressed in jeans and a diamond-patterned sweater, Agarwal welcomed me aboard and introduced me to the captain, Steve Barber, whose grey hair spilled from the back of a baseball cap.
A few minutes later, we motored slowly into Narragansett Bay. The sun was low. Directly behind the boat, the sea churned shades of grey and green. “I think we’re going to find a lot out here today,” Agarwal said, gesturing toward our frothing wake. “Because of the colour?” I asked. He nodded.
Every week since 1957, in one of the longest-running surveys of its kind anywhere in the world, scientists have come to this exact spot to study some of the most abundant and important life forms in the ocean: creatures so tiny that the vast majority are invisible to the naked eye, yet so essential to Earth’s ecosystems that our planet would be virtually barren without them – creatures we call plankton.
Plankton, from the Greek planktos-for “wandering” or “drifting”, are a large and diverse collection of water-dwelling organisms that tend to flow with currents and tides. Nearly every liquid environment on the planet is home to plankton: the ocean, of course, but also rivers, lakes, wetlands, geysers, ponds, puddles and even raindrops. Although most plankton are microscopic, a few large animals also qualify as plankton because they are such listless swimmers. Bacteria and viruses populate the smallest end of the plankton spectrum. Certain jellyfish and their relatives, some of which are more than 40 metres long with their tentacles fully extended, inhabit the other. In between bobs a panoply of strange and wondrous creatures, many of which are little known and poorly studied – despite their power to change the planet.
Agarwal slipped on mint-green rubber gloves and picked up what looked like a comically large, incredibly fine-knit butterfly net missing its handle. A metal ring propped open the mouth of the net, while its narrow tail clutched a small plastic jar known as a cod end. “This is one of the samples we’ll collect, concentrate and preserve for the future,” Agarwal said. “The goal is for water to go through the net and for things to get trapped in this little cod end. First, what we want to do is get it to sink.”
He lowered the net over the side of the boat with a rope and repeatedly dunked it into the water, the way one might dip a teabag in a mug of hot water. The net billowed stubbornly near the surface. “Ideally, when there’s a current –” Agarwal began to say, when the net suddenly straightened. “There we go. You see? It’s going to stretch out.” Soon, the greater part of its tail had sunk out of view.
Agarwal prepared a few more nets, each of which had pores of a different size, ranging from 20 microns, about the diameter of a white blood cell, to 1,000 microns, roughly the size of a large grain of sand. Collectively, the nets would trap a diverse assemblage of minuscule organisms, some of which Agarwal would take back to the lab. After waiting for 15 minutes or so, he pulled one of the nets back on to the boat, removed the cod end and poured its contents through a filter into another plastic receptacle.
At first glance, it looked like little more than water peppered with dust. As I peered closer, however, it became clear that the water was alive. The dark specks I mistook for dust were not merely floating – they were twitching. Other, tinier particles spun and sputtered. A few dime-sized jellyfish pulsated near the surface of the container, so diaphanous they seemed to phase in and out of existence with the shifting light.
“Now I’m going to concentrate this entire thing into that,” Agarwal said, pointing to a glass container. He carefully poured the sample from one vessel to another, straining it through a series of filters. As he worked, he put aside most of the clear water that passed easily through the filters and focused on the murkier fluid that was left behind. The process reminded me, once again, of brewing tea – in this case, loose leaf – except that the goal was to savour the dregs and discard everything else.
By the time Agarwal finished concentrating the sample in the small glass jar, it had developed the hue of cider. Thousands of tiny creatures – shaped like discs, rowing boats and boomerangs – were moving of their own volition. Some leapt through the water, flea-like, almost teleporting from one position to another. Others glided along like manta rays or bored ahead as though excavating a tunnel. Many of those energetic motes were likely miniature crustaceans known as copepods, Agarwal told me, and they constituted a fraction of the life in the vial. The fluid, amber and cloudy, was full of living things too small to discern without a microscope. “For every plankton you can see, there are at least 10 – maybe 100 – that you can’t,” Agarwal said. “And this is just one sample.” He looked at me with wide eyes, then out at the sea. “Now think about how much life there is in the water.”
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Before making the trip to Rhode Island, I spent many happy hours gazing at photos of plankton. Like larger and more familiar sea creatures, plankton often rely on shells or skeletons for support and protection. The sheer diversity and sculptural intricacy of these structures is staggering, far surpassing any scallop or conch. Viewed up close, some plankton look like chandeliers, wicker baskets or spunsugar confections. Others resemble the webbed sails of windmills, wheels of citrus or bits of ribbon candy. Still others call to mind pine cones, harpoons, knitting needles, meandering golf tees, inverted mushroom caps, slivers of rainbow and fireworks frozen mid-burst. Inspired by this kaleidoscopic beauty, a few 19th-century naturalists created mosaics and mandalas by arranging jewel-like plankton on glass microscope slides, painstakingly positioning each one with a single horse hair. These miniature marvels commanded high prices from collectors and delighted guests in Victorian salons.
Broadly speaking, plankton fall into two big categories – the plant-like phytoplankton and the animal-like zooplankton – though quite a few species have characteristics of both. Cyanobacteria and other microbial, ocean-dwelling phytoplankton are Earth’s original photosynthesizers. About half of all photosynthesis on the planet today occurs within their cells.
Single-celled algae known as diatoms comprise another widespread group of phytoplankton. Diatoms have glass exoskeletons: they encase themselves in rigid, perforated and often iridescent capsules of silica, the main component of glass, which fit together as neatly as the two halves of a cookie tin. A different group of microalgae, the coccolithophores, also sheathe themselves in armour – made not of glass but of chalk. They construct shells out of overlapping scales of calcium carbonate, the mineral from which limestone and marble are composed, and which was once commonly used to write on blackboards.
Just as plants form the base of the food chain on land, phytoplankton nourish the seas. Zooplankton eat their green cousins as well as each other. Radiolarians are single-celled zooplankton that, like diatoms, produce glass skeletons from silica. Their armour is typically conical or spherical, and adorned with curious spikes and projections, evoking baroque thimbles. Tintinnids, a name derived from the Latin word for “jingling”, live in bellshaped shells, using a wreath of mouth bristles to catch smaller microbes. Dinoflagellates, which often resemble spinning tops, twirl through the water using ribbon and whiplike appendages and shield themselves with plates of cellulose, the same organic compound that gives the walls of plant cells their rigidity.
The smallest plankton are consumed by larger plankton, including the larvae of fish and crustaceans, which in turn feed a succession of bigger sea creatures, from herring and squid to seals and dolphins, so that plankton ultimately support all marine life. A single drop of seawater might contain tens of thousands of plankton on average, but at times it will hold many more. When storms or shifting winds and currents transfer a surplus of deep, nutrient-rich water to the surface or rivers dump agricultural and residential fertilisers along the coast, certain types of plankton – dinoflagellates and diatoms – multiply much more quickly than usual, potentially crowding every fifth of a teaspoon of water with millions of cells. These plankton blooms, which are sometimes visible from the stratosphere, can swell to an astonishing 770,000 square miles, an area roughly the size of Mexico.
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Plankton are so tiny and ubiquitous, they sometimes seem less like creatures within the ocean than atoms of the ocean itself. Without plankton, the modern ocean ecosystem – the very idea of the ocean as we understand it – would collapse.
In the 1930s, American oceanographer Alfred Redfield observed that the average ratio of nitrogen and phosphorus in samples of water collected from the deep ocean was the same as the average ratio of these elements in the cells of phytoplankton: 16 to one. Based on decades of research, Redfield eventually argued that plankton “not only reflected the chemical composition of the deep ocean, but created it”, as biological oceanographer Paul Falkowski has put it.
As dead plankton sank into the deep sea, Redfield proposed, bacteria decomposed them into their chemical constituents, enriching the ocean depths with the exact same proportions of nitrogen and phosphorus. Plankton, he elaborated, also maintained the ratio of these elements by continuously converting nitrogen into different chemical forms as part of ecological feedback loops, similar to those that microbes orchestrate on land.
Since Redfield’s day, numerous studies have confirmed his primary insights and the existence of what is now called the Redfield ratio, though the precise processes responsible for this chemical balance are arguably some of the most important mysteries in oceanography.
Plankton are also a crucial component of both short- and long-term processes that sequester carbon and regulate global climate. Throughout its history, Earth has endured repeated periods of widespread glaciation that extinguished many species. Yet each time, our planet not only recovered but eventually flourished. This resilience hinges in part on the exceptional versatility of that abundant and gregarious element from which all Earth’s life is made: carbon. Carbon’s circular journey through air, land and sea – its perpetual shuttling between organism and environment – ultimately acts as a planetary thermostat.
Carbon dioxide in the atmosphere continuously dissolves into the ocean’s surface, where sun-loving phytoplankton incorporate it into their cells during photosynthesis. Much of this carbon is released in shallow waters when zooplankton and microbes eat and decompose phytoplankton, consuming oxygen and exhaling carbon dioxide in the process. Phytoplankton that evade consumption usually live for days or at most weeks. When they die, they bump into each other, form little clumps and begin to sink, along with the fecal pellets of zooplankton, carrying carbon to deep, cold, dense water, where it may remain for thousands of years. Some of this perpetual underwater precipitation, known as marine snow, feeds deep-dwelling creatures, but a portion continues to sink and settle on the seafloor, accumulating in layers of muck that eventually petrify and trap carbon for millions of years.
In parallel, carbon dioxide spewed by volcanoes combines with water vapour in the atmosphere, forming carbonic acid that falls to land in rain. Due to its slight natural acidity, rainwater reacts with and dissolves the planet’s crust. The chemical reactions involved in this weathering produce various minerals, salts and other molecules, which flow to the ocean via rivers, nourishing marine life. Certain types of cyanobacteria, plankton, corals and molluscs use calcium and bicarbonate ions produced by weathering to construct shells, sheaths, skeletons, reefs and stacked microbial mats called stromatolites. When such creatures die, their carbon-rich remains gradually accumulate in layers of compacted limestone sediment on the seafloor. Over great spans of time, tectonic activity subsumes and transforms the sediments, returning the carbon they contain to the planet’s surface in the form of new mountains or erupting volcanoes, thereby completing the cycle.
If Earth enters a torrential hothouse state, intense and frequent rainfall weathers rock more quickly than usual, flooding the ocean with minerals, nourishing life in the sea and removing carbon from the atmosphere
faster than volcanoes can replenish it. Over hundreds of thousands to millions of years, this feedback loop cools the Earth.
Conversely, if ice smothers most of the sea and land, the water cycle effectively stalls, the productivity of plankton and other ocean life drops, and carbon dioxide builds up in the atmosphere, eventually warming the planet. “This entire process is therefore largely controlled by life and ultimately allows life to exist on Earth,” write paleontologist Peter Ward and geobiologist Joe Kirschvink. Although some of Earth’s self-stabilising processes can operate abiotically, life has been thoroughly entangled with the carbon cycle and planetary thermostat since its emergence more than 3.5bn years ago.
Planktonic confetti and other forms of marine snow accumulate on about 60% of the seafloor today. The uppermost layers of these sediments are like slurries, almost fluffy in texture, explains micropaleontologist Paul Bown of University College London. A few feet down, as the pressure increases, squeezing out water, they develop the consistency of toothpaste. Eventually, they are compressed into rock and are either melted in the Earth’s interior or returned to the surface by, say, clashing continental plates or shrinking seas.
If you chip off a piece of the White Cliffs of Dover and examine it with an extremely powerful microscope, you will see a jumble of granular detritus. Look carefully and distinct shapes will start to emerge: bows and discs made of tiny bone-like pegs packed together as neatly as the wedges in a stone archway. If you’re extremely lucky, you might even find a relatively intact sphere of ribbed discs still clinging to one another, like a bundle of petrified doilies. You would see these things because the White Cliffs of Dover are more than just rock: they are also fossils. The cliffs’ mineral building blocks – those intricate arcs, discs and spheres visible only with a microscope – are the husks of single-celled coccolithophores that lived during the Cretaceous period between 145 and 66 million years ago.
In fact, the vast majority of chalk and limestone formations on Earth, including large sections of the Alps, are the remains of plankton, corals, shellfish and other calcareous sea creatures. Every imposing edifice that humans have constructed with limestone, including the Great Pyramid of Giza, the Colosseum and the Empire State Building, is a secret monument to ancient ocean life. And coccolithophores are not the only plankton that turn to stone, either. Millions of years ago, early tool-making humans discovered the benefits of working with flint and chert, which, unlike most rocks, are simultaneously hard, sharp and knappable. Though they had no way of knowing, they were crafting arrows and axes from the compacted husks – the glass ghosts – of diatoms and radiolarians. Stone tools revolutionised our ancestors’ diets, cultures and technologies, which is to say that the mere remnants of plankton defined the course of human evolution.
Because plankton are so ubiquitous, tiny and easily dispersed, their orbit of influence extends far beyond the ocean and coasts. Every year, the wind carries immense quantities of Saharan dust across the Atlantic Ocean, depositing 27.7 million tonnes – enough to fill more than a hundred thousand semi-trailer trucks – in the Amazon rainforest, where it provides trillions of plants with iron, phosphorus and other essential nutrients. This fertilising dust is not simply tiny bits of dirt and rock; it is largely composed of the skeletons of ancient diatoms. Much of it comes from the Bodélé Depression, a sunbaked bowl of sand that was once the bottom of an enormous lake larger than all of North America’s Great Lakes combined. Long after they have died, plankton continue to shape and sustain the planet, circulating vital elements through ocean, desert and jungle. In their aeon-spanning metamorphosis – their transformation from floating cell to entombed rock to windswept dust and back again – they embody the reciprocity of life and environment and the perpetual reincarnation of the Earth.
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In 1900, Paris hosted the Exposition Universelle, a seven-month-long world’s fair intended to celebrate the ingenuity of modern civilisation. More than 50 million people visited the fair, where they rode a moving sidewalk, watched motion pictures with sound and admired the hulking steam-powered generators behind the incandescent Palace of Electricity. The city commissioned an architect named René Binet to design the exposition’s entryway. Binet’s gate consisted of a gigantic honeycombed dome perched atop several grand archways. Decorative stone, Byzantine motifs and colourful glass cabochons covered its surface.
The architecture exuded grandeur and opulence, evoking a formal display of crown jewels, yet it was also delicate and distinctly organic. One writer of the era saw “the vertebrae of the dinosaur in the porch, the cells of the beehive in the dome and corals in the pinnacles”. But none of these creatures were the primary inspiration for Binet. His true muse was much more obscure. As he designed the Porte Monumentale, Binet routinely visited libraries in Paris to study illustrations by German scientist Ernst Haeckel.
Today, Haeckel is best known for his vivid and captivating drawings of animals, plants and fungi, especially those collected in his wildly successful book Kunstformen der Natur(Art Forms in Nature). Haeckel was enamoured of sea creatures. He especially liked the elaborate yet precise geometry of radiolarians, which appealed to his exacting aesthetic. These were the images that obsessed Binet. “At present, I am building the Monumental Entrance for the Exposition of 1900,” he wrote to Haeckel in 1899, “and everything, from the general composition down to the smallest details, has been inspired by your studies.”
Binet’s organic sculpture of stone, metal and glass was a tribute to evolution – and its power to produce astoundingly beautiful structures that often transcended human design. Given what we now know about the importance of plankton to global ecology, these towering arches – a literal gateway to a celebration of human achievement – take on new meaning. A plankton expanded into a cathedral allows what is normally unseen to mesmerise. Without me, it seems to say, you would not be here. Without me, none of this would be possible.
If plankton had not infused the sea and air with oxygen, modulated ocean chemistry and become key regulators of global climate, there would never have been forests, grasslands or wildflowers, nor dinosaurs, mammoths and whales, let alone bipedal apes gawking at moving sidewalks and incandescent lightbulbs in the early 20th century. If plankton did not exist, Earth would have no complex life of any kind.
Without the innumerable viruses, bacteria, single-celled organisms and as-yet-unclassified mysteries that we call plankton, the ocean would be completely unrecognisable: not a vast ecosystem replete with unexplored habitats and undiscovered species of inconceivable wonder – not the presumed birthplace of life and the foundation of the biosphere – but an immense volume of lonely water, brimming only with the silence of all that might have been.
This is an edited extract fromBecoming Earth: How Our Planet Came to Lifepublished by Picador and available from 29 August
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