About 4,000 years ago, Harappa's culture flourished in the Indus Valley Valley of modern-day Pakistan and Northern India. They had large, prosperous cities, invented waste water centuries before the Romans and set up long-distance trade routes to Mesopotamia. But less than two centuries, their culture faded and their cities fell – and the main culprit could be climate change.
The Hindu valley civilization was mainly urban culture, caused by overproduction of agricultural production and commerce. They prefer urban settlements and built at least two major cities: Harappa and Mohenjo Daro, which were significantly improved in time.
But things began to change around 2500 BC. The change of temperature and weather conditions across the Indus valley caused the gradual narrowing of the summer monks, which increasingly hindered farming.
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Liviu Giosan, a geologist at WHOI and lead author of the new document, says that this is what ultimately led to their death and forced them to step down slowly in smaller villages at the foot of the Himalayas.
"Although the troubled summer monsoons made farming commonplace in the Indus, mountain peaks, humidity and rain would be regular," says Giosan. "As the winter storms from the Mediterranean Sea enter the Himalayas, they created rain on the Pakistani side and fed small currents. Compared to the monsoon floods that Harappan used to see Indus, it would have been relatively little water, but at least it would be reliable."
End of the era
This is not a new theory, but in mud samples it is difficult to find evidence of these redirecting patterns. Instead Giosan and his colleagues were taken to the ocean. They looked at microscopic fossils foraminifera. Foraminifera is a primitive "living fossil" that lives in chemistry (542 million years ago) to the present day. They have fossils, which are usually made of calcium carbonate, which means they are often fossilized, especially in the Indus region. However, instead of looking for fossils, researchers looked one step deeper: they were looking for DNA snippets.
"The bottom of the sea near Indus's mouth is a very low oxygen environment, so the growth and dying in the water are very well preserved in the sediments," says Giosan. "You can basically get DNA snippets of almost anything that lives there."
"The value of this approach is that it gives you an idea of past biodiversity that you miss, relying on skeletal remains or fossil record. And since we can eventually redirect billions of DNA molecules in parallel, it gives a very high resolution of how over time, the ecosystem has changed, "adds William Orsi, a paleontologist and geobiologist at the University of Munich's Ludwig Maximilian who collaborated with Giosan on work.
This is an interesting form of indirect evidence: during the wintertime, monsoon's powerful winds absorb surface nutrients from deeper parts of the ocean, feeding on the rapid growth of plants and animals, evidence of this increase is recorded in the DNA sequences in layers of the ocean floor. DNA evidence has shown that winter monsoons seem to have become stronger, and summer monsoons are weaker than the later years of Harappan's civilization, which correspond to moving from cities to villages. It is unclear when and how soon this process took place, but it was the end of the era.
"We do not know if Harappan's caravans moved in the footsteps over the course of a few months, or this massive migration has been around for centuries. What we know is that, upon conclusion of the contract, urban lifestyles have ended," says Giosan.
This event is a very important warning today. Unlike us, Harappan did not bother about this climate change – the source of this climate has actually gone a long way. Purchasing a mini ice age, releasing cooler air from the Arctic in the Atlantic Ocean and later in Northern Europe. In turn, it delayed the cold (but rather warmer) air in northern Europe, causing storms in the Mediterranean, which caused the winter monsoon to overwhelm the valley of the Indus, a series of dominoes that arrived at the site, and the fate of the Harabpanas lights up.
A similar process is taking place today, and climate change introduces a complex mechanism that will affect parts of the world.
"This is remarkable, and today is a powerful lesson," he notes. "If you look at Syria and Africa, migration from these areas is linked to climate change, which is just the beginning-sea level rise, as climate change can lead to huge migrations from poor regions such as Bangladesh or from hurricane regions in the south of the US." Harappan can cope with change while moving, but today you will get in all directions. Then you can follow political and social cramps. "
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