From UPSC perspective, the following things are important :
Prelims level : Emergence of landmass on Earth
Mains level : Not Much
A new study has challenged the widely accepted view that the continents rose from the oceans about 2.5 billion years ago.
- Singhbhum district of Jharkhand is part of the Chhota Nagpur Division.
- It is one of the leading producers of copper in India.
First landmass to emerge
- The study suggests that the earliest continental landmass to emerge may have been Jharkhand’s Singhbhum region.
- Scientists have found sandstones in Singhbhum with geological signatures of ancient river channels, tidal plains and beaches over 3.2 billion years old.
- They somewhat represent the earliest crust exposed to air.
Studying the sandstones
- The research studies a sedimentary rock, called granite. They tried to find their age and in which conditions they have formed.
- They found the age by analysing the uranium and lead contents of tiny minerals.
- These rocks are 3.1 billion years old, and were formed in ancient rivers, beaches, and shallow seas.
- All these water bodies could have only existed if there was continental land.
- Thus, they inferred that the Singhbhum region was above the ocean before 3.1 billion years ago.
How did they analyse?
- The researchers studied the granites that form the continental crust of Singhbhum region.
- These granites are 3.5 to 3.1 billion years old and formed through extensive volcanism that happened about 35-45 km deep inside the Earth.
- This process continued on-and-off for hundreds of millions of years until all the magma solidified to form a thick continental crust in the area.
- Due to the thickness and less density, the continental crust emerged above surrounding oceanic crust owing to buoyancy.
Back2Basics: Emergence of Landmass
- In the beginning, more than 4.6-billion years ago, the world was a ball of burning gas, spinning through space.
- It took hundreds of millions of years for the first land masses to emerge.
- About 250-million years ago, long, long after the Earth had formed, all the continents of the time had joined together to form a super-continent called Pangaea.
- This super-continent broke up about 200-million years ago to form two giant continents, Gondwana and Laurasia.
- Gondwana comprised what is now Africa, South America, Australia, Antarctica and India.
- The Indian sub-continent lay off the east coast of Africa, before it broke off and moved north rapidly.
- Huge plates of crustal and upper mantle material (lithosphere) “float” on more dense, plastically flowing rocks of the asthenosphere.
- The “depth” to which a plate, or block of crust, sinks is a function of its weight and varies as the weight changes.
- This equilibrium, or balance, between blocks of crust and the underlying mantle is called isostasy.
- The taller a block of crust is, the deeper it penetrates into the mantle because of its greater mass and weight. Isostasy occurs when each block settles into an equilibrium with the underlying mantle.
- Blocks of crust that are separated by faults will “settle” at different elevations according to their relative mass.