The Vedas, The Vedas, a collection of texts composed over 3,000 years ago in India, speak of a mythical sacred river called the Sarasvati from which the Hindu goddess of science and learning emerged. Hers was a river “surpassing in majesty and might all other waters.” But around 4,000 years ago, all was lost when climate change kicked in. That is the conclusion of a group of geologists, geomorphologists, archaeologists and mathematicians who joined forces to answer a question that has dogged scholars for centuries: what became of the Indus civilization? This colossal civilization rose about 4,500 years ago, flourished for 600 years and then began a steady and relentless decline. Previous scholars hypothesized that regional strife or a foreign invasion led to its unraveling, while others suggested that environmental factors may have been to blame. The researchers who took part in the new study, published in the Proceedings of the National Academy of Sciences, had a hunch that the latter theory was correct. The Vedas, Hindu goddess of science “What we thought was missing was how to link climate to people,” said Liviu Giosan, a geologist at the Woods Hole Oceanographic Institution in Massachusetts and the lead author of the study. “The answer came when we looked at the widescale morphology.” Using satellite photos and topographical data, the researchers prepared digital maps of the Indus River landscape. They collected field samples to determine the age of sediments in the region and whether their structure was shaped by rivers or the wind. The information was then overlaid across prior archaeological findings, yielding a compelling new chronology of 10,000 years of human history and landscape changes, and what drove them. The story goes something like this: Wild, untamed rivers once slashed through the heart of the Indus plains. They were so unpredictable and dangerous that no city could take root on their banks. As the centuries passed, however, the monsoons became less frequent and the floods less intense, creating stable conditions for agriculture and settlement. Sprawling across what is now Pakistan, northwestern India and eastern Afghanistan, the Indus civilization encompassed more than 625,000 square miles, rivaling ancient Egypt and Mesopotamia in its accomplishments. In its bustling hubs, there was indoor plumbing, gridded streets and a rich intellectual life. Unlike the Egyptians and Mesopotamians, who used irrigation systems to support crops, the Harappans relied on a gentle, dependable cycle of monsoons that fed local rivers and keyed seasonal floods. But as later generations would discover, it was what the researchers call a “Goldilocks civilization.” After about 2,000 years, the window for agricultural stability closed again. As time passed, the monsoons continued to weaken until the rivers no longer flooded, and the crops failed. The surplus agriculture was longer there to support traders, artists, craftsmen and scholars . The Harappans’ distinct writing system, which still has not been deciphered, fell into disuse. People began abandoning the cities and moved eastward toward the Ganges basin, where rains were more dependable (though not dependable enough to sustain urban metropolises). The civilization dispersed, fracturing into small villages and towns. “The cities became peripheral — they didn’t abruptly disappear,” Dr. Giosan said. “But in the end, those cities were only a place for squatters.” The researchers found the dusty geologic remnants of the long-lost Sarasvati River in the sprawling desert surrounding the modern-day Ghaggar-Hakra valley. Rather than being fed by Himalayan runoff, as many scholars had assumed, the researchers uncovered evidence that her liquid sustenance came only from monsoons. As the climate became more arid, the weak rains could no longer sustain the river, it retreated into myth. Dr. Giosan suggests that the Harrapans’ fate offers lessons for today. “We think about tomorrow — we think of the lives of our children or maybe grandchildren,” he said. “But these accumulating effects of climate that are so slow, they don’t really enter our vocabulary or thinking.” Modern-day cultures and policy makers need to pay attention to “deep time,” or the very slow changes that accompany the deterioration of climatic conditions and resources, for the benefit of third, fourth or fifth generations, Dr. Giosan said. But in some cases, he adds, the changes are not so slow — for instance, the depletion of fossil fuels. “Just as the Indus civilization did, we’re depending on a resource that came and went,” Dr. Giosan said. “That resource is oil.” The Harappan (or Indus) civilization was the largest — but least known — of the first great urban cultures that also included Egypt and Mesopotamia. Like their contemporaries, the Harappans, named for one of their largest cities, lived next to rivers owing their livelihoods to the fertility of annually watered lands. “We reconstructed the dynamic landscape of the plain where the Indus civilization developed 5200 years ago, built its cities, and slowly disintegrated between 3900 and 3000 years ago,” said Liviu Giosan, a geologist at Woods Hole Oceanographic Institution and lead author of the research. “Until now, speculations abounded about the links between this mysterious ancient culture and its life-giving mighty rivers.” Today, numerous remains of the Harappan settlements are located in a vast desert region far from any flowing river. In contrast to Egypt and Mesopotamia, which have long been part of the Western classical canon, this amazingly complex culture in South Asia with a population that at its peak may have reached 10 percent of the world’s inhabitants, was completely forgotten until 1920′s. Since then, a flurry of archaeological research in Pakistan and India has uncovered a sophisticated urban culture with myriad internal trade routes and well-established sea links with Mesopotamia, standards for building construction, sanitation Systems, arts and crafts, and a yet-to-be deciphered writing system. “We considered that it is high time for a team of interdisciplinary scientists to contribute to the debate about the enigmatic fate of these people,” Giosan said. By combining satellite photos and topographic data, the researchers prepared and analyzed digital maps of landforms constructed by the Indus and neighboring rivers, which were then probed in the field by drilling, coring, and even manually-dug trenches. Collected samples were used to determine the sediments’ origins, whether brought in and shaped by rivers or wind, and their age, in order to develop a chronology of landscape changes. “Once we had this new information on the geological history, we could re-examine what we know about settlements, what crops people were planting and when, and how both agriculture and settlement patterns changed,” said co-author Dr Dorian Fuller, an archaeologist at the University College London. The findings, published in the Proceedings of the National Academy of Sciences, show that the decline in monsoon rains led to weakened river dynamics, and played a critical role both in the development and the collapse of the Harappan culture, which relied on river floods to fuel their agricultural surpluses. Once extending more than 1 million square kilometers across the plains of the Indus River from the Arabian Sea to the Himalayas and the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan, the Harappan civilization was the largest of the first great urban cultures that also included Egypt and Mesopotamia. Before the plain was massively settled, the wild and forceful Indus and its tributaries flowing from the Himalaya cut valleys into their own deposits and left high “interfluvial” stretches of land between them. In the east, reliable monsoon rains sustained perennial rivers that crisscrossed the desert leaving behind their sedimentary deposits across a broad region. Among the most striking features the researchers identified is a mounded plain, 10 to 20 meters high, over 100 kilometers wide, and running almost 1000 kilometers along the Indus, they call the “Indus mega-ridge,” built by the river as it purged itself of sediment along its lower course. In another major finding, the researchers believe they have settled a long controversy about the fate of a mythical river, the Sarasvati. Once extending more than 1 million square kilometers across the plains of the Indus River from the Arabian Sea to the Himalayas and the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan, the Harappan civilization was the largest of the first great urban cultures that also included Egypt and Mesopotamia. The Vedas, ancient Indian scriptures composed in Sanskrit over 3000 years ago, describe the region west of the Ganges as “the land of seven rivers.” Easily recognizable are the Indus and its current tributaries, but the Sarasvati, portrayed as “surpassing in majesty and might all other waters” and “pure in her course from mountains to the ocean,” was lost. Based on scriptural descriptions, it was believed that the Sarasvati was fed by perennial glaciers in the Himalayas. Today, the Ghaggar, an intermittent river that flows only during strong monsoons and dissipates into the desert along the dried course of Hakra valley, is thought to best approximate the location of the mythic Sarasvati, but its Himalayan origin and whether it was active during Vedic times remain controversial. Archaeological evidence supports the Ghaggar-Hakra as the location of intensive settlement during Harappan times. The geological evidence shows that rivers were indeed sizable and highly active in this region, but most likely due to strong monsoons. There is no evidence of wide incised valleys like along the Indus and its tributaries and there is no cut-through, incised connections to either of the two nearby Himalayan-fed rivers of Sutlej and Yamuna. The new research argues that these crucial differences prove that the Sarasvati (Ghaggar-Hakra) was not Himalayan-fed, but a perennial monsoon-supported watercourse, and that aridification reduced it to short seasonal flows. By 3900 years ago, their rivers drying, the Harappans had an escape route to the east toward the Ganges basin, where monsoon rains remained reliable.
Posted on: Tue, 07 Oct 2014 10:53:42 +0000
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