RAS question
The Aravalli Range is one of the oldest fold mountain ranges in the world, estimated to be about:
Correct answer: (B) 1500 million years.
The Aravalli Range is estimated to be about 150 crore years old, with the Aravalli mountain-building event placed around 1,800-1,500 Ma in the Proterozoic Eon.
Explanation
The best answer is about 150 crore years, the same as 1,500 Ma. The Aravalli Supergroup rocks date to roughly 1,500-2,000 Ma, and the Aravalli orogeny, the mountain-building event, is placed around 1,800-1,500 Ma. NASA Earth Observatory supports the geological setting: it describes the Aravalli Range as one of the oldest in India and says it began to rise when ancient tectonic plates collided in the Proterozoic Eon. That is why the answer must be in the very old Proterozoic range, not in the much younger figures offered in the other options.
Why the other options are wrong
- (A) 570 Ma marks the end of the Precambrian era, not the Proterozoic Aravalli formation window of about 1,800-1,500 Ma.
- (C) 350 Ma is far too young because the Aravalli Supergroup rocks are dated to roughly 1,500-2,000 Ma.
- (D) 100 Ma is much too recent for a range that NASA describes as one of India's oldest and that is linked to Proterozoic-age mountain building.
Concept
This tests the geological age and origin of Rajasthan's physiographic divisions, especially the Aravalli system. It recurs in RAS because Rajasthan geography repeatedly asks students to connect major landforms with their geological evolution.