Rain Page 4
As arid periods dried Africa’s rains, cracked the earth beneath our ancestors’ feet, and evaporated lakes and rivers, many of the animals and plants that had thrived in the waters and wet forests went extinct. Digging in an East African lake bed in 2012, the American paleontologist Christopher Brochu discovered the skulls and jaws of an ancient crocodile that grew up to twenty-five feet long. Brochu says the terrifying beast, the largest predator in its environment, probably dined on the early humans who came to the lake.
But on the evolutionary menu, the adaptable hominids on the way to becoming human ate the crocodile’s lunch. They outlived this predator and others, moving from place to place during drought and developing the first stone tools to help them cope with the new types of predators that took the beastly croc’s place—becoming the hunter instead of the prey.
The most recent 2.5 million years have been a seesaw of wide climate swings between epic rains that spread monstrous lakes across Africa and severe aridity that sucked those lakes back to dust. With each cycle of wet and dry, new species came and went. Yet ultimately, Homo sapiens persisted, even when their numbers plummeted to several thousand hardy souls in the wake of a series of mega-droughts. Many archaeologists believe Homo sapiens built their big brain power during these rain-starved times, evolving speech to share what they knew about water and food to survive famine. Others argue the periods of huge lakes and high moisture will prove more important in the story of human evolution. But whether humans rose to adapt to drowning pluvials, dusty aridity, or neither, the scientists agree that a large part of what makes us human is our remarkable ability to adapt to any conditions the atmosphere blows our way, at least any seen on Earth in the past few million years. It is the same trait that allows us to live on all seven continents, from bamboo houses on the rainiest hillsides in the world in India’s state of Meghalaya to faux adobe minimansions in the Mojave Desert.
Around 30,000 years ago, in another extreme climate swing during the last big Ice Age (appropriately named the Last Glacial Maximum), our evolutionary cousins the Neanderthals went extinct—even though they seemed ideally built for cold. Homo sapiens, their bodies seemingly made for the rain-fed tropics, continued to expand into icy Europe and around the world. After millions of years of evolution through the pluvials and the mega-droughts, we became the sole survivor of all hominids, and among the most adaptable species in Earth’s history.
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Our Ice Age images are frozen in massive ice sheets and glaciers and packed snow (and a dopey woolly mammoth that talks—in Ray Romano’s Italian New York accent, no less). But this difficult stretch of early human history was also distinct for its dryness. Despite the flood tragedies and the crop-killing torrents of history, survival proves much tougher without rain than in times of too much.
With so much of the planet’s water locked up in ice, Earth’s great evaporative engine had little fuel for rain. Sea levels dropped by more than three hundred feet. In arid sweeps of northern Africa and southern Australia, rainfall tapered to less than half its previous bounty and today’s. Their rivers and lakes vanished—along with sources of food. In a loop of depletion, less rain meant fewer trees to release water back into the atmosphere, leading to yet less rain. Most of the world’s deserts expanded. Harsh winds mounded up great sand dunes and pushed them around like Brobdingnagian chess pieces. Plants and trees could no more survive here in the desiccated soils than they could in the ice sheets draped over the Northern Hemisphere.*1
Remember rain’s role in scrubbing the sky blue? Lack of rain means lots of dust; our Ice Age ancestors gazed up at a bleak celestial sphere. Studying the sediment cores of the Last Glacial Maximum is like peeking under the bed: Scientists find dust everywhere they look. Today, the North African and Arabian deserts swirl with the greatest dust storms on Earth, mountainous yellow-brown clouds known as haboobs, visible from space. Cores from the Arabian Sea suggest the Ice Age skies were 60 percent sandier.
Early modern humans endured the cold, dust-dry times as hunter-gatherers in small, isolated groups, having spread from Africa into Europe and Asia and down into Australia. As Asian Ice Age hunters tracked caribou and musk oxen across the inhospitable white tundra we know as Siberia, they came upon a land bridge exposed by the low seas, and now humanity began to trickle into the Americas. But across all the inhabited continents, humans didn’t really spread out and settle down until another dramatic swing in climate—this time, to warmth, and the steadier rains of our own epoch.
Planetary scientists suspect changes in Earth’s tilt and orbit helped spur the great freezing and in turn the great melts, including the one about 18,000 years ago that began to release water back into our familiar cycle of rain, toward the mild climate modern humans have generally enjoyed since.*2
A drumroll is in order for the Holocene. After millions of years of heave and ho between dramatic cooling and warming, parched times and pluvials, humans in the most recent 12,000 years have lived in an unprecedented stretch of relatively stable climate. “Relatively” is the clincher. All human civilizations arose during this climate halcyon that the anthropologist Fagan calls the Long Summer. But century-scale extremes—epic droughts and ceaseless rains—regularly threaten the calm, like hurricanes slamming a normally sunny beach hideaway.
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Humans began the Holocene as happy hunters, soon to be home owners. Increased rainfall and warmer temperatures greened North America and Eurasia, and expanded the amount of livable land. Likewise in Asia, as the North Atlantic basin warmed, summer monsoons strengthened, spreading a tropical green garden of trees and plants across the region.
The kinder climate brought population growth and more permanence; a trade up from caves and pits to huts made of wood or stone. Radiocarbon dating lets scientists analyze tiny bits of seed and bone; this is how they know that people in many parts of the world lived well on wild abundance, filling up on game and native plants, fruits and nuts. This is also how they track a decline, about 8,000 years ago, in greenery across the land. The new wave of aridity coincides with a shift from hunting wild sheep to herding them, gathering wild grains to growing them.
Why the hunter-gatherers set aside spears and harpoons for sickle blades and grinding stones has been one of the great puzzles of archaeology. But the dawn of agriculture does line up with a worldwide trend of miserly rainfall, including a weakening Asian monsoon. Many scientists believe the faltering rains and worsening aridity clustered people along rivers, bringing smaller communities together to build irrigation systems and feed themselves and their neighbors. The four early civilizations of the ancient world arose in great river valleys: the Nile in ancient Egypt, the Tigris-Euphrates in Mesopotamia, the Yellow River in China, and the Indus in ancient India. Agriculture was our way of adapting to stretches of drought. For these four civilizations, it would not be enough.
In the same way Earth can support life having swung into what astrobiologists call the Goldilocks zone between Mars and Venus, rain has its just-right sweet spot for humans. Rain’s temperament can mean the difference between food and famine, health and plague, social unrest and national content. Years of too much can bring plague and pestilence. Years with too little stretch on with hunger and desperation. In the end, no condition proves as devastating as when rain disappears—extreme drought that can last hundreds of years. As miserable as it can sometimes be, humans have never been able to live without their color-giving rain.
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*1 While most of North America was covered in ice, there were regional exceptions to the aridity. Winds swooped glacial air to warmer regions including today’s western United States, bringing a record pluvial that created mega-lakes. Lake Bonneville spread across almost all of Utah before it turned into its famous salt flats.
*2 Paleolithic people did endure another cold and rainless millennial 13,000 years ago, the Younger Dryas. The name comes from an alpine flower, white dryas, whose ancient pollen in ice cores shows scientists when tun
dra replaced forest in the Northern Hemisphere. The Younger Dryas may have been sparked by an asteroid impact or mega-flood of North American glacial meltwater into the Atlantic that disrupted the ocean’s circulation for a thousand years. It appears to have slowed the march of humanity in the Northern Hemisphere; populations declined or plateaued in all lands north of the equator.
TWO
DROUGHT, DELUGE, AND DEVILRY
In northwest India and Pakistan, the largest of the early civilizations in the ancient world lies buried under golden sand. Unlike the Egyptian tombs or the ziggurats of Mesopotamia, most of the lost cities of the Indus Valley Harappan people are not yet excavated, their mysterious script not fully deciphered. But archaeologists working in the ancient cities of Harappa and Mohenjo Daro have revealed a remarkably advanced culture beneath the desert.
Nearly 5,000 years ago, the Harappan people lived in planned cities with walls, wide streets, reservoirs, and the first urban sanitation works. Their brick homes had hearths, wells, pipes, and rooms for bathing. Granaries and other agricultural ruins hint at major farming and trade networks that served tens of thousands of people.
All of this life flourished on monsoon rains and rivers. The vast majority of Harappan sites have been found along large river channels carved into the desert, now ghost rivers visible only in satellite imagery. Around 4,000 years ago, the people began to abandon their advanced cities. Harappan civilization slowly disintegrated.
Ever since the lost cities of the Indus Valley were discovered in the 1920s, scholars have disagreed about the reasons for their demise. The Hindu holy text known as the Rig Veda, written in an early form of Sanskrit beginning about 1750 B.C., held an intriguing clue. The Rig Veda describes a mythical river that once ran parallel to the Indus Valley, flowing from the Himalayas all the way to the Arabian Sea. Appearing in the text more than seventy times, the Saraswati River was often interpreted as metaphor. But scientists say that it was something more.
In recent years, research into the region’s past climate has uncovered a dramatic shift in rainfall patterns. Searching in an ancient rain-fed lake in northern India, paleoclimatologists using radiocarbon dating have discovered that 4,100 years ago, the summer monsoons began a rapid decline. They did not return to normal for two centuries.
For an unimaginable two hundred years, the Harappan region saw hardly any rain. Around the same time in China, Egypt, and Mesopotamia, the three other earliest-known civilizations also were lost to the dry sands of history.
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In the 1920s and ’30s, the British anthropologist C. Leonard Woolley—think Indiana Jones with high cheekbones and kneesocks—led the excavation of Ur, one of the largest and wealthiest city-states in ancient Mesopotamia (from the ancient Greek for “land between the rivers”) at the confluence of the Tigris and Euphrates in the Middle East. Newspapers worldwide reported on the tombs he uncovered in Ur’s royal cemetery, and the extravagant treasures inside: jewelry and garments made of gold, lapis lazuli, and carnelian; bowls of alabaster; solid-gold weapons; bejeweled animal figures mythical and real. The public was captivated particularly by the tales of small cups near the remains of attendants who died with their masters, headline-making evidence of ritualistic suicides. One tomb held seventy-four of the sacrificial victims.
The book of Genesis names Ur as the birthplace of Abraham. The son of a clergyman, Woolley tapped his biblical knowledge and the passion of his faith to draw people to his finds. Tourists including European royals and the queen of mystery, Agatha Christie, descended on the remote Iraqi desert from around the world to see its excavation. The crime author took the Orient Express to Baghdad and hung around Woolley’s dig to gather color for her book Murder in Mesopotamia.*
Woolley was convinced that he would next find proof of Noah’s flood. He remained so focused on the deluge that he may have set archaeology back half a century in finding the real event—quite the opposite calamity—that devastated Mesopotamian culture.
Along with their fiction-inspiring burials, Mesopotamian people cultivated Western civilization well before the ancient Greeks. The Sumerians, who built a dozen cities including Ur, carved into clay tablets with wedge-shaped styli to leave the first record of written language. They conceived the first written philosophy and laws; in architecture, the column and the arch; in math, the concept of zero. But a little over 4,000 years ago, three-fourths of Mesopotamian settlements were abandoned during an epic drought that seared for three hundred years. Some of the civilization’s greatest contributions, including the written and spoken languages, were lost for thousands more.
If only for some rain, students of the classics might be practicing their ancient Sumerian, alongside Latin and Greek.
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About 4,300 years ago, a king called Sargon of Akkad seized power in Mesopotamia, grabbing both the agricultural hinterlands in the north and the growing city-states to the south. Over the next century, Akkad and his sons and grandson built the world’s first empire, ruling from the headwaters of the Tigris and Euphrates all the way to the Persian Gulf. The rain-fed northern plains fueled a large and lucrative agricultural bureaucracy. Their written records show the Akkadians controlled and taxed production and traded long distance for barley and wheat.
In what is now northern Syria, the Akkadians erected monumental buildings at Tell Leilan, with city walls, expert canals, huge agricultural projects, and an impressive military. And then, after a hundred years of prosperity, people across the empire suddenly abandoned the cities and farms.
Carved in cuneiform script in the wake of the fall, an epic poem called the Curse of Agade (or Akkad) blames divine retribution from Enlil, a raging storm god responsible for the worst of floods and droughts. The composition describes “great agricultural tracts” that “produced no grain” and “gathered clouds” that “did not rain.” Scholars always read the curse as metaphor, much like the lost Saraswati River of Hindu lore. They blamed the collapse of the empire on managerial incompetence, overpopulation, invasion, and various other theories.
But in 1993, the Yale archaeologist Harvey Weiss, who heads the university’s Tell Leilan excavation, essentially declared that the cuneiform scribes had it right. The city once so grand that its walls still rise above the Khabur Plains had been blanketed with windblown sand for three hundred years, a time of virtually no human habitation.
In Tell Leilan and beyond, at site after site across the Habur and Assyrian Plains, Weiss and his colleagues find cities abandoned 4,200 years ago—no grains, no ceramics, no signs of humanity for three centuries, just a thick veil of dust. With no rain to moisten the soil for all that time, even the earthworm holes disappear.
The desiccation spread far beyond the Middle East. Lake-bed soils in Africa, dust content in ice cores from northern Peru, ancient stalactites hanging from caves in China and India, and pollen samples from North America all point to a worldwide crisis of drought, with aridity off the charts compared with the rest of the Holocene. Conditions looked more like the Younger Dryas, which decreased human populations across the Northern Hemisphere 13,000 years ago.
The rainless centuries line up with not only the downfall of Mesopotamia and the disappearance of the mighty Harappan civilization, but also the collapse of the Old Kingdom of Egypt along the Nile. In China, scientists note the demise of a number of Neolithic populations, a shift from agricultural-based cultures back to pastoralism, and a marked decline in the number of archaeological finds along the lower basins of the Yangtze and Yellow rivers.
Time and again through the Holocene, as rain goes, so goes civilization. For more than ten centuries until A.D. 900, the Maya flourished in the lowlands of Central America, reaching a population near ten million and reliant on delicate water management in a drought-prone terrain. Like the great civilizations of the Indus, Tigris-Euphrates, Nile, and Yellow rivers, the Maya could overcome droughts that stretched years or even decades. But a three-hundred-year dearth of rain—lake-bed cores show that i
t lasted from 750 to 1025—proved too much.
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If drought brings death in slow motion, we think of deluge as wielding it in a flash flood. In most cases, rain is not the deadly element in flood; that is wind and tidal surge, the forces that washed away up to half a million souls in what is believed the deadliest storm in history, the Great Bhola Cyclone of 1970 that drowned Bangladesh at the Bay of Bengal. Hurricane Mitch in 1998 was one great exception to the rain rule. Its fierce winds, waves up to 44 feet, and astonishing rains destroyed vast regions of Central America. The mountains of Honduras and Nicaragua milked as much as 75 inches of rain from the hurricane, which created great floods and mudslides that swept away entire villages and their inhabitants. More than 11,000 people were killed and 3 million more left homeless.
Like the worst droughts, though, the worst deluges have often been those that unfolded slowly, dragging on for decades or centuries. For all its color and life, too much rain for too long settles with grim darkness: mold, rot, and floodwaters that never seem to drain; clouds of mosquitoes outside and fevered disease within; dread to inspire Shakespeare’s Macbeth.
This may never have been truer than during the Middle Ages, when Europe wasted in some of the heaviest rains in human history. In the fifteenth-century woodcut The Four Horsemen of the Apocalypse by the German artist Albrecht Dürer, foreboding storm clouds frame the four riders—Death, Famine, War, and Plague/Pestilence. Endless rains could presage at least three of them.
In medieval Europe, the 1300s marked the beginning of a five-century climate shift known as the Little Ice Age. Persistently copious rains, floods, snows, and early and late frosts led to widespread crop failures, famines, social instability—and fear that would ignite paranoia. The second decade of the 1300s was the rainiest in a thousand years. Severe, near-constant storms thundered down in brutal surprise. One wet summer followed another. Temperatures were exceptionally cold. Electrical storms brought steady and severe lightning strikes. People rarely saw the sun, whose absence ruined grape harvests and salt production. Chroniclers of the day often used the metaphor of the Great Flood to describe the conditions; they believed God must be punishing humans for their sins, including the wars under way around Europe.