In order to understand the geological history of India, we need to first understand the geological history of the Earth.
Let me first tell you how geologists have divided earth’s history.
Earth was formed 4.5 billion years ago
and these 4.5 billion years are divided into four Eons: Hadean, Archean, Proterozoic and Phanerozoic. Hadean Eon is named after Hades, he was the Greek god of underworld. Archean is derived from Greek word Arche which simply means “beginning or origin”. Proterozoic is made up of two words Protero and Zoic and Protero means former and Zoic means life. Phanerozoic is also made of two Greek words- Phaneros and Zoe, Phaneros means visible and Zoe means life and the word Eon means “a very long period of time”.
Eons are further divided into Eras and Eras are divided into Periods and Periods are divided into Epochs.
Just like a year is divided into months, months are divided into weeks, and weeks are divided into days.
Now let’s talk about Earth. In the beginning Earth was red hot ball of molten rock. There was no life, no structure, no water. After 50 crore years earth cooled down and these 50 crore years are known as Hadean Eon.
After Hadean Eon, started Archean Eon. It lasted for 150 crore years. After Archean, Proterozoic Eon started and it lasted for 196 crore years. After this, Phanerozoic Eon started and it’s the most important Eon for the development of life on earth. Everything from Coal to Dinosaurs, to Humans and other animals appeared during this Eon. As Phanerozoic Eon is a very important Eon, it’s further divided into three Eras – Paleozoic, Mesozoic and Cenozoic.
Paleozoic era is further divided into 6 periods – Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. Mesozoic era has been divided into Triassic, Jurassic and Cretaceous periods. The cenozoic era has been divided into Tertiary and Quaternary periods.
Now let’s go back to the beginning and see how India’s geology was affected by these Eons, Eras and Periods.
As I told you earlier, earth was a hot boiling fireball during the Hadean eon, so there are no rocks found from this eon in India. Let’s move to Archean eon.
The first rocks on earth were formed during the Archean eon and these rocks are known as Archean Rocks. These rocks are not available in original form. They have been metamorphosed into Gneiss and Schist. These rocks do not contain any sign of life, because there was no life during or before their formation. Gneiss is the most important Archean rock covering about two thirds of the Peninsular surface, when we look at its mineral composition it varies from Granite to Gabbro and the schist contains mica, talc, hornblende, sillimanite and graphite.
In India, Archean rocks are found in southern parts of Indian peninsula, Orissa, Chhattisgarh, Chotanagpur Plateau, Madhya Pradesh and from Vadodara to Aravalis. These rocks also form the major part of greater Himalayan ranges.
The second rock to be formed during Archean eon in India was Dharwar rocks. But, how was these rocks formed?
The weathering of Archean gneiss and schist rocks yielded large amount of sediments and these sediments were further metamorphosed into Dharwar rocks. Dharwar rocks includes metamorphosed as well as sedimentary rocks. These rocks are called dharwar rock system because they were first studied by geologist in the Dharwad district of Karnataka.
Dharwar rocks are economically the most important rocks because high grade iron ore, gold, lead, mica, copper, manganese, quartzites are found in this rock system.
The dharwar rocks are found in abundant quantity in Dharwar-Bellary-Mysore belt of Karnataka. It also occurs in Jharkhand, Madhya Pradesh, Chhatisgarh, Odisa, and in Aravali hills.
Dharwars rocks are also found in Himalayas and Meghalaya plateau.
Now, let’s move further to the Proterozoic Eon, a very long time passed and the rocks of Dharwar system were weathered and deposited into great synclinal basins and Cuddapah rocks were formed. At some places in southern India, Cuddapah rocks are around 6,100 meters in thickness.
Cuddapah System is named after the Cuddapah district of Andhra Pradesh where it’s first studied.
Economically these rocks are important because these rocks contain ores of iron, manganese, copper, cobalt, nickel, barytes, jasper, asbestos, steatite and cherts. The also contain large deposits of building purpose quartzites and cement grade limestones.
Cuddapah rocks are found in Andhra Pradesh, parts of Orissa, Chhattisgarh and Karnataka. These rocks are also found in a narrow strip from Delhi to Aravali and Gujarat.
Vindhyan System: This rock system derives its name from Vindhyan Mountains. Vindhyan rocks contain diamond bearing rocks and the mines of Golconda and Panna are very good example of it.
The Vindhyan system provides red-sandstone, sandstone, building material, ornamental stones and raw material for cement, lime, glass and chemical industries. The historical buildings of Qutab Minar, Humayun’s Tomb, Fatehpur Sikri, Agra Fort, Red Fort, Jama-Masjid, and Sanchi Stupa have been constructed from the red-sandstone from the Vindhyan ranges.
Gondwana System: It derives its name from the Gond tribe of India. These rocks were mainly formed from Carboniferous period to Jurassic period. The main areas of Gondwana rocks in India are along the Damodar Valley, Mahanadi valley, and Godavari valley. Economically, the Gondwana rocks are the most important because they contain about 98% of the coal reserve of India. They have rich deposits of iron ore, copper, uranium and antimony. Fossils are found in these rocks.
The Deccan Trap: Trap is Swedish word, and it means Stair. From the end of the Cretaceous till the beginning of the Eocene epoch, volcanoes started to erupt in the peninsular India and an area of 10 lac square km was flooded by basalt lava.
Basalt is main rock found in Deccan trap, dolorite, rhyolite, gabbro and many other rocks are also found. These rocks are great source of quartz, agate, calcite, building stones and road building material. The weathering of these rocks has also given birth to black cotton soil also known as ‘regur’.
The Tertiary Period: Himalayas were formed and Indian subcontinent broke apart from super continent Pangea.
Quaternary Period: The northern plains of India formed during this period. Karewa deposits of Kashmir were formed during this period. Karewas are well known for cultivation of saffron, almond, and walnuts.