The formation and development of Earth have always intrigued researchers and for this very reason, they are constantly involved in the analysis of ancient rocks.
A recent study on the rock sediments published in the Proceedings of the National Academy of Sciences (PNAS) has underscored that Earth's first continents may have risen out of the ocean around 700 million years ago and that the first stable continental land to have risen about 3.2 billion years ago may have been Singhbhum region of Jharkhand.
| First Stable Continents The first stable continents were known as Cratons that emerged from the ocean 250 million years ago. These were formed before the existence of plate tectonics, a major driver for increasing elevation in the landmasses today. |
The team of researchers from India, Australia, and the US have acquired the sandstones in Singhbhum having geological signatures of ancient river channels, tidal plains and beaches over 3.2 billion years old.
The study's lead author, Dr. Priyadarshi Chowdhury of Monash University, was quoted by The Guardian as saying, "We realised these were ancient riverine [rocks], formed in rivers and estuaries. We have plate tectonics today to control the elevation. When two continents’ [plates] collide, you form the Himalayas, you form the Alps. That wasn't the case 3 billion years ago."
How did the earliest continents on Earth come into existence?
Scientists have hypothesised that the earliest continents have risen out of oceans as a result of 300 to 400 million years of continuous volcanic activity.
The Singhbhum craton may have been formed from a pile of lava over time and the crust which is approximately 50km deep became so thick that it floated on the water just like an iceberg.
The team of researchers extracted zircon from the Singhbhum sediments. They estimated the age of the rocks by shooting lasers at the zircon and then measuring the relative amounts of elements released. The technique is
The cratons similar to that of Singhbhum exists in South Africa and Australia.
The researchers believe that the weathering of the cratons would have led to nutrient runoff, supplying the ocean with phosphorus and other building blocks for early life.
Once a landmass is created, shallow seas such as lagoons are also created, thereby accelerating the growth of oxygen-producing life forms that may have boosted oxygen in the atmosphere and ocean.
The emergence of early continents would also have drawn carbon dioxide down from the atmosphere, leading to localised pockets of cold climate and the formation of glaciers which was the first step towards making the Earth more habitable.
Also Read | Why most of the world’s tropical deserts located on the Western margins of continents?
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