Gaia is a thin spherical shell of matter that surrounds an incandescent interior; it begins where the crustal rock meets the magma of the Earth's hot interior, almost 100 miles below the surface…. I call Gaia a physiological system because it appears to have the unconscious goal of regulating the climate and chemistry at a comfortable state for life.

—James Lovelock1

Viewed from afar, Earth is a thing of beauty. White clouds swirl across the blue orb, bright deserts reflect warm sunshine, and green vegetation marks fertile landscapes. Not just beautiful, but geophysically, climatologically, and biologically interactive. Using Gaia—goddess of the Earth—as a metaphor, James Lovelock claimed that the geophysical planet and its biota were a mutually stabilizing, self-balancing, holistic entity. First framed at a time when ecologists found equilibria wherever they looked, the Gaia Hypothesis was enthusiastically embraced. That was back in the 1970s. Unfortunately, things look very different today.

The first data to shake the Gaia mentality came from Greenland's thick ice-cover; the second were deposits on the floor of the North Atlantic Ocean. Cores into both ice and sediment revealed a hundred thousand years in which sudden climatic shifts had taken place with some frequency. Not only had ice ages come and gone, but on some occasions climate had changed abruptly within a decade. Gaia wasn't supposed to work that way! Perhaps ocean currents, coursing across the North Atlantic, had suddenly changed direction. Then came another nasty surprise: atmospheric research revealed an expanding “ozone hole” high above Antarctica. Human-devised chlorinated cooling agents were disintegrating in the frigid stratosphere and destroying ozone in our upper atmosphere! And, as if all this weren't trouble enough, the world's been getting warmer!

Over a century ago, chemists had predicted that pumping ever more carbon dioxide into the atmosphere would warm the globe. Carbon dioxide has an unusual property: it is transparent to higher energy ultraviolet radiation but absorbs lower energy infrared energy. Ultraviolet energy from the Sun passes through the atmosphere, strikes the Earth, becomes converted to infrared and is re-radiated outward. It is this re-radiated energy that is partly absorbed by greenhouse gases and keeps our planet comfortable, rather like a blanket or the air within a greenhouse. Consequently, a higher concentration of CO₂ will cause greater planetary warming. Alaska's weather is changing especially fast. Inuit people of the far north are seeing robins for the first time; their language has no name for this distinctive bird. As carefully recorded over the last 1,200 years, Japanese cherry trees are now blossoming earlier than ever before. Our biosphere is getting warmer.

Gaia cannot cope! Though half our carbon dioxide emissions find a home in the ocean, soil, and plant life, the other half is being added to our atmosphere. Also, by producing agricultural fertilizers, humans are now fixing as much nitrogen as all the rest of the biosphere, and this is changing aquatic ecosystems. Having reached his nineties, Lovelock has lost his optimism and now sees Gaia as capricious. But how did this come to pass? How could humans have become so powerful a force, on so grand a planet, in so little time?

THE AGRICULTURAL REVOLUTION

Homo sapiens could never have become the highly technological, environment-dominating and environment-transforming animal of today if agriculture had not been invented.

—Paul Ehrlich and Anne Ehrlich2

Agriculture was truly something new and revolutionary. The balance between humans and the rest of the biosphere was decisively altered.

—Jeffrey Sachs3

Humankind's most significant recent advance may have been a natural outcome of increasing cultural sophistication in response to mankind's ever-present fear: starvation. Though hunter-gatherers had survived the ice ages in both tropical and temperate environments, our numbers remained small. As with every other species, human survival was precarious. Local populations were regularly challenged by prolonged drought, unusual cold, or virulent pathogens. Finding enough food to survive and reproduce was a never-ending challenge. Then suddenly—within a geological instant—our species diminished its likelihood of starvation by initiating a series of new symbiotic relationships! We call these innovations agriculture and animal husbandry.⁴

By nurturing a few carefully chosen species of plants and animals, humans assured themselves a more reliable food supply. Herding sheep and goats may have come easily for nomadic hunters. Capturing young animals and caring for them afforded a ready supply of meat and hides. Since these animals lived naturally in small social groupings, they adapted well to their new masters. Soon we were corralling, breeding, and herding them. Best of all, these hoofed animals eat plant materials we humans cannot digest, allowing more of our number to prosper in grasslands and thorn bush. In different parts of the world, sheep, goats, cattle, donkeys, horses, camels, yaks, and llamas became essential members of human communities. Chickens in southern Asia and turkeys in Mexico added to the feast. Though dogs had been our hunting companions for perhaps 20,000 years, both dogs and pigs, feeding on village refuse, became part of the menu in many cultures.

Learning to plant and tend selected plants may have been more challenging than herding sheep and goats. Finding nutritious plants amenable to cultivation, planting and weeding them, carefully harvesting, then separating and storing seeds for next year's planting, were sophisticated new activities. Perhaps most extraordinary of all, these life-transforming advances were initiated by people in several corners of the globe independently! Agriculture in the New World arose totally apart from that practiced in the Old World. North America's first settlers were pre-agricultural hunting bands. By three thousand years ago, Mexican and Mesoamerican farmers were growing maize, squash, tomatoes, cacao, avocado, papaya, and vanilla, as well as local varieties of chili peppers, kidney beans, and cotton. People in South America, from the high Andes to the Amazon lowlands, first domesticated potatoes, cassava, sweet potatoes, pineapples, peanuts, and tobacco. They, too, came to grow distinctive varieties of maize, beans, chili peppers, and cotton.

In the Middle East, agriculture appears to have arisen earlier than in the New World. Here, people were nourished by durum wheat, barley, bread wheat, chickpeas, lentils, olives, grapes, dates, figs, and many other foods. People first used bananas, several kinds of melons, eggplant, mangos, and many other fruits and vegetables in southern Asia. Several varieties of rice and millets, as well as soybeans, were first developed in eastern Asia. Inhabitants of New Guinea and the western Pacific were the first to harvest sugar cane, local yams, taro, and coconut palm. Western and northern Africa are the original home of sorghum, yams, several millets, indigenous melons, okra, oil palm, native cotton, and cola seeds. Highland Ethiopia is the home of the world's smallest cereal grain (teff), a banana relative used for starch (ensete), a useful oil (noog), a stimulating beverage (coffee), and distinctive varieties of both sorghum and barley.

Around a thousand years ago, people in eastern North America were cultivating native goosefoot and marsh elder, as well as new varieties of sunflowers, pumpkins, and maize. Among all these many plants grown around the world, grains (from the grass family) and pulses (from the legume family) became widely used staples. Other cultures used root crops as their primary starch source, such as potatoes in the high Andes and cassava in the Amazon basin. Because they lived on the same supercontinent and along similar latitudes, cultures in Asia and Europe easily shared crops and domestic animals. Overall, agriculture was initiated between ten thousand and five thousand years ago in several regions of the world. More to the point, agriculture allowed us to store nourishment for bad times, becoming the most successful species the world had ever seen!5

While we still do not understand why so critical an advance in human history occurred at this particular period in time, the results have been transformative: agriculture fed more people more reliably! After the introduction of agriculture, habitation sites in Western Europe expanded ten-fold in area, implying a ten-fold increase in local population! That was the good news, but agriculture had downsides as well. Living a sedentary life in close contact with domesticated animals fostered more diseases. In crowded settlements, people often suffered nutritional deficiencies, becoming smaller than their nomadic antecedents. Nevertheless, these negative effects had little impact. Agriculture allowed humans to beget more humans. Called the Neolithic Demographic Transition by historians, our increasing numbers advanced the elaboration of human societies.

Viewed from the perspective of the Red Queen, humans were beginning to run a lot faster than anyone else. Agriculture had boldly increased our species’ fitness. A world abundant in biodiversity provided the resources on which this advance was constructed. From amongst more than 260,000 described species of flowering plants, twenty-five species provide more than 85 percent of our daily energy requirements! (This includes the plants that nourish the animals we eat). A few thousand additional flowering plant species give us important spices, oils, condiments, fibers, and medicines. Without this grand diversity, we could not have provisioned so grand an expansion of human numbers. And let's not forget the soil. Farming depends on soils that have become organically enriched over many millions of years. Similarly, coal, oil, and gas are all the products of earlier life activities, empowering today's industrial societies.

FEEDING THE MULTITUDES

Agriculture allowed larger numbers of people to live together in stable settled communities. In turn, larger sedentary human communities allowed for both stratification and specialization. Men as hunters and warriors, and women as nurturing mothers and gatherers, had been playing their essential roles for thousands of generations. But now, with agriculture and increased numbers, larger human societies began to behave like “superorganisms.” Resembling the castes found within insect colonies, one human caste could be devoted to food production, others to working wood or metal, and others waging war. Even so, biology determined destiny. Females were absolutely critical in birthing and rearing the young; our large brains required constant nurturing. Males, with greater upper-body strength, tilled the soil, worked metal, constructed buildings, and defended the community.

Not only did larger agricultural populations expand human demands and intensify human competition, they provided a platform for further rapid and far-reaching innovation. As Geerat Vermeij has written, “Competition in the broadest sense…is universal in all economic systems, including life itself, at every scale of inclusion.”6 Regardless of whether the economy was fueled by photosynthesis in natural ecosystems or driven by the territorial imperatives of feuding human polities, competition within and between societies has made us who we are. It is our species that now stands at the pinnacle of earthly dominion. Our croplands and pasturelands are today's largest terrestrial ecosystems.

Thanks to agriculture, forestry, aquaculture, animal husbandry, fishing, and other activities, we are currently devouring over 30 percent of the Earth's net primary productivity.⁷ Agriculture was the foundation on which the further advance of industrially powered human societies was constructed. Humans and their “agricultural symbionts” have become one of the most transformative symbioses in the history of life. We propagate and carefully tend rice, sheep, pigs, potatoes, and lots more; then we eat them!

Settled villages, supported by agriculture, provided humans a launching pad for a new trajectory—accelerated cultural and technological advance. While nomadic hunters may have been efficient in survival and added new information to ancestral lore, their numbers remained small. Suddenly, along major rivers and with carefully engineered irrigation, agriculture could support thousands of our kind. Strategically located villages blossomed into city-states, providing a new platform for human advancement. Protected within the city's walls, people were free to utilize their many talents and fashion innovations.

Ovens for baking bread and firing useful ceramics were soon followed by forges working metal. Early copper work was followed by an age of bronze in the Middle East. Here again, our planet played a critical supporting role. Three tectonic plates abut in the Middle East. This is where minerals—molten at great depths—became concentrated and returned to the surface, explaining why metallurgy began so early in this corner of the world. (The island of Cyprus is named for copper.) Then, using hematite as a flux in working copper, and perhaps accidently, metal workers of the Middle East began extracting iron from a reddish rock. High temperatures under low oxygen levels allowed charcoal to remove oxygen from hematite, yielding metallic iron, and this, with a dash of carbon, gave us steel. Farmers and warriors demanded stronger, harder, sharper metals. Steel tools felled forests more quickly, plowed the ground more effectively, and waged war more ruthlessly. Requiring high and precise temperatures, metallurgy was another singular advance in our species’ advance.

Cities promoted the division of labor and technological innovation. Planting crops in seasonal environments required understanding the Sun's annual cycle: the beginnings of astronomy. A wide variety of wild plants provided medications; their proper identification and careful application fostered the rise of medicine. Agricultural transactions demanded accounting; writing followed quickly. Easily stored and transported, cereal grains and pulses fed the masses and fueled a mobile military. Guarding transportation routes, imposing order, and fending off attacks, armies promoted commerce while securing empires.8 Stone tools had changed little over thousands of generations during our early history, but now, with settled agricultural societies, human technologies advanced rapidly.

Much earlier, and as the only species on the planet to be fearful of the future, humans had developed mythic traditions. Religious belief infused our lives with hope and meaning, strengthening our resolve in the face of uncertainty and calamity. In urban centers, religious expression fostered unity, supported a ruling elite, and inspired monumental architecture. Religious values validated jurisprudence, providing order in crowded societies.9 Claiming divine sanction, rulers promised justice and stability. All the while, diverse human talents found new opportunities within the city-state. Prodded by wealth and warfare, urban people conformed their lives, advanced their skills, and prospered like never before.

Cultural advance, however, has differed greatly around the globe. Native Australians and other isolated groups remained hunter-gatherers. Native Americans developed a rich agricultural tradition and created complex societies with impressive monumental architecture; however, they had no strong draft animals, and lacked iron and steel. In contrast, the people of Europe, North Africa, and Asia shared a vast land area replete with rich and varied resources, Novel discoveries and continuous interaction allowed Eurasian societies to become richer and more complex.¹⁰

Social norms influenced progress as well. Around 1450 CE, China chose condescending isolation to more dynamic interaction, even as Europeans were beginning to explore the world. Mediterranean cultures proved more adventurous, perhaps as a consequence of active trading and incessant warfare. By 600 BCE, state-supported currency had accelerated Mediterranean trading. Lacking a strong religious priesthood, classic Greece was free to foster philosophy and science, even experimenting with democracy. Later, Rome excelled in law and civic engineering, managing a grand empire over five hundred years. Two hundred years after Rome's collapse, Islamic societies fashioned a trading network linking Morocco to India and China. Having taken control of Samarkand, the Islamic world was introduced to Chinese papermaking, the perfect medium for recording and translating earlier knowledge into the language of the Koran. Between about 800 and 1100 CE, with new mathematical techniques, adopting a numbering system from India and studying both vision and astronomy, scholars writing in Arabic grandly advanced the sciences. Tragically, with the destruction of Baghdad's libraries by Mongol invaders in 1258, the Islamic efflorescence wilted. Around the same time, with knowledge translated from Arabic and Greek into Latin, scholarship became revitalized in Western Europe.

A SCIENTIFIC REVOLUTION

Looking at the history of science, we do find a net increase in the empirical success of our theories and unquestionably also an increase in the degree to which they constitute a unified, integrated, mutually supported network.

—Keith Parsons11

Blessed with good weather from the tenth through early fourteenth centuries, Europe grew in population and prosperity. Divided by mountain chains, and with many regional principalities, Europe could not be bound into a single empire as was China. Sharing a single language—Latin—for both religious and intellectual discourse, European culture proved open and innovative. Beginning with a compendium of Roman law, Medieval Europe created a pragmatic new civil legal system, marginalizing religious jurisprudence and fostering a more dynamic mercantile society.¹² Because of its many navigable rivers and mineral resources, Europe's growth shifted northward, away from the Mediterranean. Challenged by newly translated Arabic and Greek texts, European scholars began their own intellectual journey. Claiming that a closer study of nature would illuminate our understanding of God, Medieval Christian philosophers gave social sanction to the careful study of God's creation. Shifting away from the certainties of traditional knowledge, scholars now confronted what we did not understand. In this way, Western Europe began an intense examination of the natural world.

Calamity briefly intervened. With increasing trade from the east, Europe was assaulted by a virulent pathogen. Beginning in 1347, the Black Death nearly halved the population of Europe. But again, and as elsewhere in the history of life, calamity afforded new opportunities. Following Europe's pandemic, individual labor became more valuable, land became less expensive, and a Renaissance soon blossomed. All the while, marine transport along both Atlantic and Mediterranean shores continued apace. The stern-post rudder, compass, and gunpowder (all from China) accelerated naval activity. Prosperity sharpened Europe's appetite for tropical spices, fine ceramics, and Chinese silks. Satisfying these demands would create wealth for trader, merchant and banker.

To this purpose, Prince Henry of Portugal initiated a program of naval exploration southward along the western coast of Africa. Sturdy little ships, caravels were built to explore unknown shores and return with knowledge for further voyages. These many expeditions achieved their goal in 1497, when Vasco da Gama sailed southwest across the Atlantic toward Brazil, turned eastward to catch the prevailing winds, and circumnavigated Africa to reach Calicut, India. Portugal's naval exploration had linked Portugal to India, providing Europe with precious goods at lower costs. Indian Ocean navies confronted these invaders, but the Portuguese had cannon balls to spare. Earlier, in 1492, certain that he could reach Asia more directly, Columbus sailed directly westward across the Atlantic. Instead of Asia, he collided with a “New World,” making clear how much was yet to be discovered!

Europe's own inventions, such as iron horseshoes, eye glasses, mechanical timepieces, and double-entry accounting, led to greater efficiencies in agriculture and commerce. More fundamentally, Europe had a free and open market system. Legal agreements and interchangeable currencies provided a social technology in which commerce would flourish. Paper-making reached Italy in the late 1300s. This useful medium allowed Johan Gutenberg to print books using precisely fashioned interchangeable metal type. Costly manuscripts, laboriously hand copied in times past, were suddenly affordable in printed form. Printers and their presses (as venture capitalists) moved across Europe, grandly expanding the sharing of knowledge. In stark contrast, both China and the Islamic world shunned Gutenberg's technology for almost two centuries. With affordable Bibles and his own vernacular translations, Martin Luther urged Christians to study the scriptures for themselves. Challenging Vatican authority in this way, Europe became convulsed in religious and political turmoil, even as commercial activity and scientific inquiry expanded.

Around 1608, a Dutch optician devised the first telescope, allowing him to see farther more clearly. Learning of this invention, Galileo constructed his own in 1610, watching as four moons circled Jupiter over the following weeks. Viewing Venus over several months, Galileo witnessed the phases of that planet as it journeyed around the Sun, exactly as Copernicus had proposed! About the same time, and using Tycho Brahe's carefully recorded planetary observations, Johannes Kepler deduced the rules of planetary motion. Considering this astronomical data from the perspective of a falling apple, Isaac Newton explained planetary motion with the elegant concept of universal gravitation in 1687. Exactly as natural philosophers had claimed, careful observation revealed God's universe was governed by laws! The scientific revolution had begun.

AN INDUSTRIAL REVOLUTION

Industrialization made possible immense improvements in human health and longevity, while providing ordinary people with greater material welfare than their ancestors could ever have imagined.

—Patrick Alitt13

Growing in population, enmeshed in constant warfare, and demanding goods from all around the world, Europeans were consuming ever more resources. By the late 1600s, the British Isles were suffering a timber famine. Warships, general construction, and the need for firewood had devoured forest and woodland.¹⁴ Coal proved to be an efficient replacement for heating needs, but coal mines flooded frequently in rainy Britain. Steam engines, developed in the mid-1700s to pump water out of the flooding mines, converted heat into work. By the early 1800s, more efficient steam engines were propelling cargo along rails of steel. Railroads were a new kind of technology—rail lines, engines, cars, and stations in a linked network. Factories with steam-powered looms made cotton textiles more affordable. Also, as the economy grew, Europeans craved more sugary sweets. Intense demand for both sugar and cotton gave rise to a harsh industrial slavery in the Americas, even as European peasantry was conscripted into factory labor. All the while, modern capitalism accelerated economic advance by investing surplus profits into further production and innovation.

Coal-powered steam engines had begun another grand advance in the human saga. No longer limited to human, animal, wind, or water power, the Industrial Revolution ran on fossil fuel. Powered by this energy-dense legacy of ancient life, both human numbers and human technologies expanded at an ever-quickening pace.15 Scientific investigation and experimentation, publicly vetted and subject to verification, produced extraordinary dividends. In 1821, Michael Faraday showed that a rotating magnet generated electric current in a copper wire. A few decades later, engineers were transmitting electric power over long distances. Using small confined explosions, the reciprocating internal combustion engine proved both efficient and mobile. In 1915, one-fifth of America's farmland was devoted to feeding horses; they were soon replaced by gasoline-burning tractors. Having seen Chicago butchers process beef on overhead conveyers, Henry Ford assembled automobiles more rapidly with overhead assembly lines. In turn, affordable automotive transport accelerated commerce and expanded personal freedom. Heavier-than-air flight, first by propeller, then by jet, allowed us to traverse the planet, transporting both people and precious goods quickly over large distances. Today, consuming large stores of energy-dense fossil fuel, we enjoy lifestyles unimagined in earlier times.

Energy consumption has been central both to the evolving odyssey of life and to our ever-expanding human economies. For over two billion years, oxygenic photosynthesis provided the living world its motive force. Concentrated over many millions of years, ancient life has given us fossil fuels rich in chemical energy. Beginning the Industrial Revolution with coal, fossil fuels expanded technological development with oil and gas, and now support lifestyles of ever-greater comfort. Heated in winter, cooled in summer, with refrigerated foods throughout the year and jetting to destinations around the world, we humans are consuming more and more fossil energy. Modern society and its many technologies mark the most recent chapter in Earth's ever-increasing complexity. Biological evolution, working slowly over millions of years—powered by the Sun—resulted in greater biodiversity and more elaborate ecosystems. More recently, we humans discovered new ways of improving our lives, at first with simple hunting tools and fire, later with agricultural crops and domesticated animals. Today, modern societies are energized with fossil fuels, atomic fission, water power, wind, and sunshine. All the while we mine rich ores concentrated over billions of years by the Earth's dynamic geology. Empowered in these various ways, we are elaborating our technologies more rapidly. But before we engage the consequences of our technological advance in our final chapter, let's take a quick look back over Earth's long and episodic history of ever-increasing complexity.