The earliest rocks in the earth's crust are Archean rocks, also known as Pre-Cambrian rocks. The Archean epoch accounts for 86.7 percent of the earth's whole geological history, making it extremely important. This time period saw the emergence of the first photosynthesis, as well as the evolution of the life-supporting environment. In India, the Archean or Purana rock system may be found in the Aravallis highlands, two-thirds of the Deccan peninsula, and sections of the north east. This article will explain to you about the Archean System which will be helpful in Geography preparation for the UPSC Civil service exam.

Archean System (Precambrian Rocks)

• The oldest rocks, which date back to the Precambrian epoch, were produced roughly 4 billion years ago.
• Rocks developed as molten lava solidified - the earth's surface was very hot at the time.
• They are the oldest and serve as the foundation for additional layers. They are known as the 'Basement Complex.'
• In India, Archean rocks are known as Purana Rocks, which means "oldest rocks."
• In India, the Archean or Purana rock system may be found in the Aravallis highlands, two-thirds of the Deccan peninsula, and sections of the north east.
• Metallic and non-metallic minerals such as iron, copper, manganese, bauxite, lead, zinc, gold, silver, tin, tungsten, mica, asbestos, graphite, and others abound in these rocks.
• The exposure of gneisses and granites, particularly on the Peninsula, represents it.
• The Archaean system's rocks are predominantly found in Karnataka, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, Orissa, Jharkhand's Chotanagpur plateau, and Rajasthan's southern-eastern region.
• They may be found in the Aravalli Hills, the Deccan Plateau, and India's northeast.
• They're also found in the roots of mountain summits all across the Greater Himalayas, as well as the trans-Himalayan Zaskar, Ladakh, and Karakoram ranges.
• They are the basement complex or foundation rocks for other rock systems that cover about two-thirds of Peninsular India.
• Two rock systems make up the Archaean group:
• Schists and Gneisses are found in the Archaean System, whereas the first sedimentary rocks are found in the Dharwar System.

Archaean Schists and Gneisses

• These rocks are the oldest pre-Cambrian rocks, dating back around 4 billion years.
• Rocks developed as molten lava solidified - the earth's surface was very hot at the time.
• They are the oldest and serve as the foundation for new layers. They are known as the 'Basement Complex.'
• As these are volcanic in nature, they are Azoic or unfossiliferous, Foliated, consisting of thin sheets), Thoroughly crystalline Plutonic intrusions, volcanic rocks discovered deep inside.

Dharwar System

• The age of formation spans from 4 billion to - 1 billion years.
• Sedimentary rock system that has been highly metamorphosed, produced through transformation of Archaean gneisses and schists deposits.
• They're the oldest metamorphosed rocks on the planet.
• Found in abundance in the Dharwad district of Karnataka.
• Economically the most important rocks because they possess valuable minerals like high grade iron-ore, manganese, copper, lead, gold, etc.

Archean epoch

• The origins of life on Earth and evidence of cyanobacteria may be traced back to 3500 million years ago.
• Simple single-celled creatures without nuclei, known as Prokaryota, were the only ones who could live.
• The atmosphere was devoid of oxygen, with a pressure ranging from 10 to 100 atmospheres.
• The Earth's crust had cooled sufficiently to allow continents to develop.
• Archean rock formations are the earliest rock formations on the planet's surface.
• With multiple lava outbursts, volcanic activity was much higher than it is now.
• Due to dissolved carbon dioxide, the waters were more acidic than they were during the Proterozoic.
• Plate tectonics may have been comparable to that of the contemporary Earth towards the end of the Archaean.
• There was a lot of liquid water, and deep oceanic basins were known to exist.
• The oldest stromatolites have been discovered in a 3.48 billion-year-old sandstone in Western Australia.
• Stromatolites, which are microbial mats generated in shallow water by cyanobacteria, are the oldest recognisable fossils.

Conclusion

The Archean epoch is particularly significant since it accounts for 86.7 percent of the earth's whole geological history. The earliest rocks, dating from the Precambrian period, were formed around 4 billion years ago. As molten lava hardened, rocks formed; the earth's surface was very heated at the time. Karnataka, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, Orissa, Jharkhand's Chotanagpur plateau, and Rajasthan's southern-eastern area are home to the Archaean system's rocks.