Vast Expanses

A History of the Oceans

Helen M. Rozwadowski

• Editorial: Reaktion Books
• Año: 2018
• ISBN:
  9781789140293
• Categoría: History
• Categoría: World History

Much of human experience can be distilled to saltwater: tears, sweat, and an enduring connection to the sea. In Vast Expanses, Helen M. Rozwadowski weaves a cultural, environmental, and geopolitical history of that relationship, a journey of tides and titanic forces reaching around the globe and across geological and evolutionary time.Our ancient connections with the sea have developed and multiplied through industrialization and globalization, a trajectory that runs counter to Western depictions of the ocean as a place remote from and immune to human influence. Rozwadowski argues that knowledge about the oceans—created through work and play, scientific investigation, and also through human ambitions for profiting from the sea—has played a central role in defining our relationship with this vast, trackless, and opaque place. It has helped us to exploit marine resources, control ocean space, extend imperial or national power, and attempt to refashion the sea into a more tractable arena for human activity.But while deepening knowledge of the ocean has animated and strengthened connections between people and the world's seas, to understand this history we must address questions of how, by whom, and why knowledge of the ocean was created and used—and how we create and use this knowledge today. Only then can we can forge a healthier relationship with our future sea.

ONE

A Long Sea Story

All sea stories are true.

– Various mariner-storytellers¹

POETS AND ORDINARY PEOPLE alike profess their love for the ocean, but the ocean does not love us back. It simply exists, although it does not exist simply, and it has done so since long before Homo sapiens evolved. Contrary to the tendency to think of it as a timeless, constant place, the ocean has changed dramatically over time. Throughout its mutable, four-billion-year lifespan thus far, it has played a leading role in nurturing life and fostering its diversity. As products of the profusion of life, humans were connected to the ocean first evolutionarily. Its natural history comprises, then, the earliest chapters of the story of the long human relationship with the ocean.

LIQUID WATER MAKES our blue planet distinct from all others in the solar system, making the formation of the ocean the first chapter, or at least the prologue, in our long story. Water became locked into Earth’s earliest rocks as they took shape from dust particles in space to which water molecules adhered. On the early Earth, any water brought to the surface would have been released as steam, as rising temperatures melted rocks, and escaped from Earth because there was no atmosphere to trap it. Comets and asteroids carry water, and it appears that asteroids delivered the water that stayed on Earth as temperatures cooled and an atmosphere formed. Several cycles ensued of cooling, raining and continued asteroid bombardment that boiled off the water to produce dense steam, followed by rain once again as cooling continued.

From these processes, the ocean emerged about four billion years ago, only half a billion years after the planet itself took shape. At first, oceans covered most of the Earth’s surface. Minerals that dissolved from submerged rocks and gases released by volcanoes and geysers entered the water, setting in motion the geochemical cycle that has kept the chemical composition of the ocean constant for a billion years.

In that primordial ocean, long before land emerged, rocks formed that provide evidence that life might have evolved and gained the capacity to photosynthesize by 3.8 billion years ago. Found now in southern Greenland and formed on an ancient sea floor, the Isua sediments are the oldest known rocks created at the planet’s surface rather than deep in its interior. Actual microfossils of bacteria have been found in rocks dated to 3.5 billion years ago. The oldest ones were discovered in a Western Australian rock formation known as Apex Chert. This dark-grey, carbon-rich rock was laid down along the edges of a seaway near a volcano whose lava flowed over the seabed and sealed the fossils in place. Eleven kinds of thread-like microbes, some new to science and others indistinguishable from living cyanobacteria, reveal the ocean environment as host to morphologically diverse life extremely early in the Earth’s history.

Until 3.9 billion years ago, our planet was bombarded with material from space, and a mere 65 million years ago a cosmic impact ended the age of dinosaurs. Any life that emerged early might easily have been destroyed, so that there may have been multiple life-starting events on Earth. Yet all life forms on Earth today are nearly chemically identical, and their roots trace to the same parental cell line. So it seems that one appearance of life took hold at an auspicious moment in the Earth’s development. By contrast, prebiotic evolution of sorts happened on some asteroids but did not result in life, suggesting that water was critical.

While the evolution of life from non-life remains one of science’s most enduring mysteries, one fact is known with confidence – that the ancient ocean played a major supporting role in this primordial drama. The most prominent spokesperson for evolution, Charles Darwin, recognized the centrality of a watery environment with characteristics different from the present Earth in his famous ‘warm little pond’ surmise, when he described to Joseph Hooker the conditions under which organic molecules might have given rise to a living organism.² His vision resembled that posited by scientists today: lagoons, lakes, puddles, groundwater and oceans enriched with organic compounds that, when exposed to atmospheric gases and stimulated by electricity, could produce molecules such as amino acids, sugars and other building blocks for life.

While we can be confident that the ocean served as life’s cradle, there are several candidates for which part or parts of the ocean fostered this momentous innovation. Deep oceanic settings would have provided a refuge from cosmic bombardment. Areas at or near the sea floor would have available ferrous iron, dissolved from rocks, an essential catalyst for the synthesis of organic compounds. The discovery in 1977 of hydro-thermal vents on the sea floor opened up a new possibility: that life evolved in proximity to deep-sea vents emitting hot water and gases. Vents likely served as a source of carbon for organic synthesis and, because they pump a volume equivalent to the world’s oceans every ten million years or so, they regulated the chemical composition of the ocean.

For more than three billion years, life on Earth consisted of single cells or aggregations of cells that formed mats of microbes covering the sea floor. Not until some bacteria developed the ability to photosynthesize would the Earth’s atmosphere gain oxygen. Accumulation of oxygen in the atmosphere, and eventually circulating throughout the seas, set the stage for multicellular organisms that could survive, and ultimately thrive, in the once-toxic soup of oxygen. Although earlier animal fossils have been found, those of the Cambrian period, starting about 540 million years ago, reveal a wild proliferation of life forms, all oceanic.

THE OCEAN’S ROLE in accommodating the stunning variety of life over the sequence of geological periods contributes a noteworthy series of chapters in our long story. The aptly termed Cambrian explosion generated the first representatives of many of today’s taxonomic groups. The trilobites, early arthropods, dominated the period and spread over the globe. With their armoured external skeletons, these creatures swarmed throughout the warm, shallow seas for over 270 million years, filling a wide variety of ecological niches as predators, scavengers and plankton eaters. Other life forms included algae, invertebrates, echinoderms and molluscs, but not yet vertebrates nor terrestrial plants or animals. Adjacent to the diverse oceans, the land was relatively barren. Life did not yet exist in freshwater.

Much is known about Cambrian life thanks to the exceptional preservation of fossils, including their soft parts as well as their hard shells. In 1909, palaeontologist Charles Walcott discovered fossils in the Burgess Shale formation in the Canadian Rockies and dedicated his summers to collecting thousands of specimens. Decades later, scientists recognized the diversity and unfamiliarity of the fauna in his collection and made the Burgess Shale justifiably famous as a resource for studying evolution. Stephen Jay Gould’s 1989 book, Wonderful Life, argued that Cambrian life displayed more diverse forms than exist on Earth today and posited that many of the unique lineages went extinct and, thus, represent evolutionary dead ends.

The spectacular fossil records of the Cambrian also record permanent changes to the sea floor. Competition for food in shallow seas promoted use of bottom sediments for avoiding predators and searching for food. Burrowing animals initially fed upon and were protected by the microbial mats covering the sea floor. Animals burrowing vertically began to break down the mats and make the upper layers of the sea floor softer and wetter. Their actions also allowed oxygen to penetrate below the sea floor’s surface, irrevocably changing the environment at the bottom. In response, organisms dependent on microbial mats went extinct, to be replaced by new species adapted to the new conditions. Unfortunately for future palaeontologists, this dramatic environmental change also meant the end of conditions that permitted the exceptional preservation of fossils such as those in the Burgess Shale.

In the post-Cambrian era, life flourished in the stabilized, shallow marine environment. About 500 million years ago the first vertebrates appeared – eel-like creatures that lacked jaws and paired fins but sported a primitive backbone, head and tail. Unable to swim, they probably spent their lives wallowing on the muddy seabed, ingesting small food particles by filter feeding. At least two classes of jawless fish evolved, diversified and went extinct, or virtually so, during the Palaeozoic era (from 543 to 248 million years ago), but other fish classes that appeared during that time remain with us today. The lampreys and hagfishes in our seas have evolved a wide range of specialized lifestyles from parasitism to scavenging, to filter feeding. Their taxonomic status is disputed, but they might be descended from ancient classes of jawless fish.

Cartilaginous fish, including sharks, rays and skates, have skeletons made of cartilage, not bone, and further differ from bony fish in their lack of swim bladders and lungs. They pre-dated dinosaurs by about 200 million years and survived to fascinate us in the present. Sharks emerged 400 million years ago and proliferated in the Carboniferous period that followed. Some groups survived massive changes to the oceans, which caused several major extinction events and killed other marine life. Modern sharks first patrolled the seas as dinosaurs roamed but lived on after dinosaurs disappeared, numbering among the most ancient creatures on Earth today.

Bony fish, also still common in our seas, included a group that evolved into amphibians, which only late in the Palaeozoic era ventured onto land. Both ancient and modern amphibians remained closely associated with water. They had aquatic larval phases and required wet environments for laying eggs and for keeping adult skin moist. Reptiles evolved characteristics that finally broke life’s ties to the sea. Hard-shelled eggs and scaly, dry skin retained moisture, freeing reptiles, and subsequently birds and mammals, to spread inland and across the globe to fill all types of environments.

Sea-floor spreading broke the supercontinent Pangaea into separate landmasses that began moving towards their current positions. Smaller divisions brought more land in contact with the ocean and created a sea between the African and Eurasian landmasses, which was christened the Tethys Ocean by the Austrian geologist Eduard Suess in 1893. Named after the sister and consort of Oceanus, the ancient Greek god of the ocean, and extant for 250 million years until destroyed by the movement of continents, the former Tethys exists today in the form of oil deposits in the Middle East and off West Africa and eastern South America that represent 60 to 70 per cent of the world’s oil. Rocks in the Swiss Alps once lay in the western end of this lost sea, which extended in the late Cretaceous to cover what is now the Sahara Desert in North Africa, as well as vast parts of the North American Midwestern plains. Sea levels rose as the former Tethys Ocean floor bulged upwards, leaving only 18 per cent of the planet dry at the zenith of this episode of sea-level rise.

The Mesozoic era, or Age of Reptiles, was flanked by two extinction events. The largest mass extinction ever occurred 252 million years ago, eliminating 70 per cent of terrestrial species and over 90 per cent of marine species including the highly successful trilobites. As new life forms spread, dinosaurs dominated the planet for 135 million years. While schoolchildren everywhere know about the Age of Dinosaurs, few of us realize that this geological period could as accurately, though much less glamorously, be dubbed the ‘Age of Oysters’.³

The oceanic food chain then, as now, depended on phytoplankton, primary producers that transform sunlight into food and provide sustenance for zooplankton. New microscopic plants and protozoans appeared, including coccoliths, diatoms, foraminifera and radiolarians, all of which produced shells, or tests, that contributed to different types of sea-floor sediments and chalks commonly found today. Molluscs proliferated, especially clams and snails that could burrow into the sea-floor sediment to escape the numerous predators in Mesozoic seas. The hard shells of oysters often proved insufficient protection from the powerful claws of crabs and lobsters, while starfish appeared whose suction feet were strong enough to pry shells apart. Nor were molluscs safe from predators who lived above the sea floor. Among the marine reptiles, placodonts used broad teeth to crush shells of oysters and limpets. Some sharks and rays, even certain fish species, could defeat the armour of many molluscs, possibly to the point of causing the disappearance of entire species of bivalve brachiopods.

Henry de la Beche, Duria Antiquior, 1830: the first pictorial representation of deep time.

Open waters above the rough-and-tumble seabed were home to many species of cephalopods, a taxonomic group today represented only by squid, octopus and nautiloids. Coiled shelled ammonites evolved rapidly and spread widely throughout the seas. Many were likely good swimmers and formidable predators, with jaws capable of spearing or crushing prey, while others free-floated at various depths. Ammonites ranged in size from the diameter of a quarter-dollar coin to as much as 2 m (6½ ft), and filled many ecological niches. Their extreme abundance makes them excellent index fossils, helping geologists identify rock layers in which they are found, while their beauty attracts collectors.

Even the largest ammonites were dwarfed by the carnivorous marine reptiles that shared their seas. Discovery of large fossils of plesiosaurs or ichthyosaurs in the nineteenth century fascinated the public and encouraged reputable scientists to consider seriously that sea monsters might still exist. Icthyosaurs, striking examples of convergent evolution for their similarity in form to dolphins, were admirably adapted to Mesozoic seas, with well-developed paddles for locomotion and long bills with teeth for catching fish. As today’s marine mammals did, they evolved from land-based species. While most ichthyosaurs were only 3 to 5 m (approx. 10 to 15 ft) long, some were 15 m (49 ft). Plesiosaurs had whale-like bodies, short tails and paddle-shaped fins. Long-necked forms that resemble the cartoon image of Nessie, the Loch Ness monster, are most familiar in popular culture. The smallest species measured around 2 m (6½ ft), while the largest could be 20 m (65½ ft) long, as large as today’s sperm whales. These big marine predators pursued fish, sharks, ichthyosaurs, dinosaurs and other plesiosaurs.

The Mesozoic chapter closed dramatically with a mass extinction best known for killing off the dinosaurs, sparing only species that would evolve into modern birds. Possibly set in motion by an asteroid impact about 66 million years ago that left the Chicxulub Crater on the Yucatán Peninsula, 50 per cent of all genera disappeared globally in a short geological period, including the ichthyosaurs and plesiosaurs that had ruled the seas, and all the ammonites, but also many species of micro-plankton, brachiopods, fish and land plants. In place of the large reptiles, birds and mammals diversified and remarkably rapidly filled every available ecological niche, including in the seas. Our own geological era, the Cenozoic, witnessed the evolution of land-based species of mammals into marine creatures.

Popular literature often featured illustrations such as this one from 1874, of a battling ichthyosaur and a plesiosaurus, by French illustrator Édouard Riou.

Fossil skeleton of an early form of whale in Wadi Al-Hitan, the Valley of the Whales, a palaeontological site southwest of Cairo, Egypt.

Why did mammals return to the sea? Seafood might be the answer. Marine mammals first appeared as global temperatures and primary productivity in the oceans increased during the Eocene, and all groups evolved adaptations for fe...

Índice

• Front Cover
• Half Title
• Title Page
• Copyright
• Contents
• Introduction: People and Oceans
• 1: A Long Sea Story
• 2: Imagined Oceans
• 3: Seas Connect
• 4: Fathoming All the Ocean
• 5: Industrial Ocean
• 6: Ocean Frontier
• 7: Accessible Ocean
• Epilogue: Ocean as Archive, Sea as History
• REFERENCES
• BIBLIOGRAPHY
• ACKNOWLEDGEMENTS
• PHOTO ACKNOWLEDGEMENTS
• INDEX