Delhi Ridge: An Ecological Marvel

In 1986, an archaeologist named S S Saar made a startling discovery. Walking in the middle-class South Delhi neighborhood of Malviya Nagar, he noticed a mysterious glint in a pile of sand. Mixed in with the sand, which had been dumped there by a crew of construction workers, he found a handful of ancient stone tools, carved from quartzite.

This inspired another archaeologist, A K Sharma, to find the source of these tools, and his search eventually led him to Anangpur, a village just beyond the southern boundary of Delhi, where largescale quarrying operations had been initiated as part of larger efforts to mine the Ridge. A series of archaeological expeditions followed, and the research teams found thousands of stone tools scattered through the area, evidence of a large Stone Age site of habitation. Despite the fact that many stone tools had been destroyed or misplaced in the process of mining, Anangpur remains one of the largest Stone Age sites discovered in India.

If not for the construction boom in Delhi, and the need to dig up the Ridge’s rocks and sands for building, Delhi would still be ignorant about the largest settlement of its earliest human inhabitants. Those intent on building a new Delhi couldn’t help but dig up the past, quite literally. And all that digging inevitably circles back to the Ridge, the source of the city’s geological riches.

Geology has played a pivotal but often overlooked role in the development of both historical and present-day societies, and Delhi is no exception. Geology underlies our lives, not just physically, but economically, socially, and technologically. Consider, for instance, the absolute centrality of fossil fuels to modern life. The industrial revolution was propelled by steam power, which depended on the fossilized remains of vast coal deposits from the Carboniferous (literally, “coal-bearing”) Age, about 300 million years ago. Similarly, the political economy of the twentieth century hinged on the geological remnants of the Cretaceous Period 100 million years ago, when vast gas and oil reserves formed due to a lack of oxygen in the deep sea. The geology of Delhi may not have such global resonance; nonetheless, every society in Delhi’s history has drawn on the unique geology of the region, from the Stone Age to the present day.

Those who ignore Delhi’s geology do so at their own peril. In September 2014, newspapers reported yet more delays in the construction of the city’s “Signature Bridge”, which was meant to be completed for the 2010 Commonwealth Games. The culprit this time: an “unexpected rock profile” on the riverbed. Bridge, meet Ridge. Anyone familiar with Delhi’s basic geology would know that the above-ground outcrops of the ancient Aravallis peter out precisely at the section of the Yamuna where the bridge was being built. But the Aravallis keep on going underground, all the way to Haridwar, covered by relatively recent alluvial deposits from the river systems of the “young” Himalayas. The rock profile found by the bridge engineers should not have been so unexpected after all.

Though the stones of the Ridge form the foundation of much of Delhi, they remain largely hidden from view. They are buried underground (or underwater) or hidden by shrubs and thorns, with only the occasional boulder visible on higher ground. What follows in this chapter is a work of excavation, unearthing the ridge-ness of the Ridge. For these stones have a story to tell, not just about geology, but about the hunter-gatherer prehistory of Delhi, the bloody travails of the medieval period, the rise of imperial bureaucracy, the struggles of the city’s workers, and the dreamy imagination of the city’s elite.

I am hardly the first to be interested in these stones. Delhi has long been home to people whose lives and livelihoods depended on the region’s geology, from our hominid ancestors who first found toolworthy material in eroding stones to the modern-day contractors selecting the best type of sand for making concrete. They are all geologists in the broadest sense of the term; their understanding of the Ridge’s rocks has pushed forward scientific and technological advances and pioneered new methods of using Delhi’s natural resources, in both constructive and destructive ways.

The Stones Come Alive

For the Paleolithic inhabitants of Delhi, one stone would have held particular importance: quartzite. This is the stone from which so many tools were crafted, the stone that S. S. Saar stumbled upon so fortuitously. Quartzite can be found in abundance throughout the Aravalli range, which begins in Gujarat, traverses all of Rajasthan, and ends with the low hills of the Delhi Ridge. Once a grand mountain chain, the Aravallis have been subject to erosion and gradual weathering over the course of more than a billion years. However, quartzite is particularly resistant to erosion, and so it remains prominent in many parts of the range, including the Ridge. It would have been a beacon to early tribes.

Although these tribes seem to exist in the farthest reaches of the ancient past, they are of remarkably recent vintage when compared to the quartzite they were so adept at shaping. Quartzite appeared to the tribes as a fixed, permanent substance, with a solidity and heft that proved useful for many purposes. Indeed, this is how quartzite appears to us today. But when considered on a sufficiently vast timescale, the stones of the Ridge (quartzite and all the others) take on a life of their own, clashing and clanging and eroding and re-forming over many millennia.

Before zooming in on a more intimate, human-centered timescale, it is worthwhile to meditate for a moment on the unfathomable expanses of geological time. The quartzite of the Ridge is 1.5 billion years old, the same age as the Aravalli Range itself. It is 7,500 times older than humanity and 150,000 times older than the birth of agriculture. No wonder it seems so constant to humans.

To understand how quartzite formed, and why it has properties that have been so useful to Stone Age and modern humans alike, we’ll have to take a brief plunge into the forbidding, Greek-inflected jargon of geologists. For instance, the oldest time period on the geological time scale is called the Hadean eon, named after Hades, Greek god of the underworld. The name is meant to evoke the fiery, “hellish” conditions on Earth at the time, as much of its surface was still molten; the technical term is “extreme volcanism”. In those times, there was more lava than rock, and the Ridge was still waiting to be born.

The oldest rocks in the Aravallis are around 3.3 billion years old, significantly predating the formation of the mountain chain. This marks them as products of the Archean eon, when the Earth was beginning to cool. Appropriately, the term “Archean” comes from the Greek word for “beginning” or “origin”; Earth’s geology, including our little corner of it, the Ridge, properly starts in this eon. After the end of Hades’ reign, various continents began to take shape. The basic constituents of these continents were cratons: stable, thick pieces of the Earth’s crust.

From around 3 to 2.5 billion years ago, there was a period of rapid thickening in the craton that now hosts the Delhi Ridge. Evidence of this can be found in an analysis of the present-day Aravalli mountain range, which reveals an ancient formation at its base, dominated by granitic rocks. During the Archean eon, the crust in the Aravalli region was at least twenty kilometers thick.

The next eon, the Proterozoic, was when the Ridge as we know it took shape. Geology is not a field known for its ironies, but it is surprising to learn that the mountains of the Ridge actually began as a basin.4 Although the immediate cause of the Aravallis’ formation was the pushing together of land, it has its origins in the pulling apart of the Earth’s crust.

This process, known as rifting, began approximately 2.5 billion years ago and continued until about 1.9 billion years ago. The craton that had grown so thick in the Archean age of beginnings began to thin out in the Aravalli region, as tectonic forces started pulling it apart. Fiery heat returned to the Ridge, as magma burst through the cracks in the earth. Due to all this thinning out, a large basin formed, which began to collect volcanic rocks, as well as sedimentary ones like sandstone.

Rifting was followed by about 300 million years of cooling as the crust settled back into an equilibrium. But this equilibrium would not last long. The main event was about to start: the “Delhi orogeny”. On a normal human timescale, this event would hardly be perceptible. A human would not find much change in the Aravallis even during its most drastic periods of transition. But if we speed up our timeline, and take in a billion years at a time, we can see how transformative the Delhi orogeny was.

Excerpted with permission from Fractured Forest, Quartzite City by Thomas Crowley, jointly published by SAGE Publications and Yoda Press under the Yoda-SAGE Select imprint.

Watch Thomas Crowley in conversation with Mini Menon, as they discuss more about Delhi’s Ridge and its ecological history here-