The Bedrock on Which India Stands

It has been an ancient place of worship, steeped in legends; it has acted as a bastion against enemies and even today, Nandi Hills, about 40 kms from the Bengaluru International Airport, attracts scores of tourists who come to see the old Shaivite temple or the fort that was once used by Tipu Sultan here. But few who make their way up the hill realize its actual significance. The Nandi Hills are part of the very bedrock - the building block, of the Indian subcontinent. It has been around for 3.5 billion years!

– The Dharwar Craton has been around for 3.5 billion years

These hills are part of the Dharwar Craton, which is the earliest building block of the Indian landmass. The Dharwar rocks lie exposed in a discontinuous arc that begins in northern Karnataka and after passing through central and eastern Karnataka, ends close to Bellary. They are called the Dharwar rocks after the town of the same name and on a map appears as a V-shape in Western Karnataka.

To understand the significance of the Dharwar Craton or the Nandi Hills you have to go back to the formation of the Earth itself.

Our Earth was born around 4.567 billion years ago. At first, the Earth like any other newly formed planet was just a hot ball of iron that spun around the Sun. The Sun itself, was recently formed about 5 billion years ago, therefore unstable and its gravitational pull (the force that helps planets in their orbits), varied making the movements of these young planets erratic.

– A craton is an old stable part of the Earth’s outer layer

About 3.2 billion years ago, rocks like the granite which makes up the Nandi Hills and the Dharwar Craton were beginning to form. Technically speaking ‘a craton’ (Greek for strength) or a shield is an old stable part of the Earth’s outer layer (the crust). A craton is that part of the Earth’s crust that has remained largely unchanged for billions of years. The rocks that make up the Nandi Hills near Bengaluru originated from this period and became the bedrock around which the newer rocks aggregated to create peninsular India, which was assembled, piece by piece.

Another interesting example of this kind of rock can be seen in the heart of Bengaluru as a large grey outcrop of peninsular gneiss that sits in the middle of the famous Lalbagh Botanical Gardens. This rock formation is protected by the Geological Survey of India as one of the oldest rocks in the world.

– This rock formation is protected by the GSI as one of the oldest rocks in the world

Geologist believes that the Dharwar rocks underlie much of peninsular India, especially Karnataka, Northern Tamil Nadu, Maharashtra, Andhra Pradesh, while the younger rock was added over the next million years in Odisha and Bengal, thus forming the pedestal upon which India sits. The other parts of India are much younger.

About 300 to 200 million-years-ago, the super-continent of Pangea (Greek for ‘all-earth’) was formed. It is hard to believe, but at one time all the continents were fused together and formed one supercontinent. Later, around 200 to 180 million years-ago Pangea broke apart and formed Laurasia (which included present-day Europe, Asia minus India, and North America) and Gondwana (including present-day India, Africa, South America, Madagascar, Australia, and Antarctica). Interestingly the name Gondwanaland was coined by geologist Eduard Suess and was inspired by the Gondwana region of central India, one of the oldest known regions of the world.

– At one time all the continents were fused together and formed one supercontinent

The breakup of Gondwana occurred in stages to form the continents which we see today. The breakup and was not a one-time event. The first stage of its breakup began in the Early Jurassic Period, about 180 million years ago long before the early hominids were present on earth. The western half of Gondwana (Africa and South America) separated from the eastern half (Madagascar, India, Australia, and Antarctica).

The South Atlantic Ocean opened about 140 million years ago as Africa separated from South America. At about the same time, India, which was still attached to Madagascar, separated from Antarctica and Australia, opening the central Indian Ocean. During the Late Cretaceous Period, 118 million years ago, India broke away from Madagascar, and Australia slowly drifted away from Antarctica.

After the separation from Madagascar, Greater India (Indian peninsula) embarked on one of the longest journeys undertaken by any land mass. While drifting northward, around 68 million-years-ago, greater India stepped over the Reunion hotspot causing massive outpourings of lava over land and sea.

– The Kailash temple in Ellora is the product of the volcanic lava flow that created the ‘Deccan Trap’ 68 million-years-ago.

Between 68 and 65 million-years-ago, copious amounts of lava flowed which deposited over a larger area in Western part of India and thus were formed the present-day Western Ghats. Interestingly, The Kailash temple in Ellora (also known as cave no.16), one of greatest architectural wonders we have, is the product of the volcanic lava flow that created the 'Deccan Trap' 68 million-years-ago. Carved out of single stone, the Ellora caves owe its grandeur to the softness and consistency of the volcano rock from which it is chiseled. It was built from the top down, instead of being built from the bottom up. To put the age of the Nandi Hills and the Dharwar Craton in context, these are 3.5 billion years old. The Western Ghats are around 65 million years-old and the Himalayas are the youngest, about 50 million-years-old.

That should induce you to spend an extra day in Bengaluru, the next time you are there!

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