In November 2021, scientists from India, Australia, and the US said that the first continental land may have emerged about 3.2 billion years ago in Singhbhum region of Jharkhand, India. It is a landmark discovery which has challenged the long-standing notion that the continents first emerged from the ocean about 2.5 billion years ago. The new study suggests that this phenomenon would have occurred around 700 million years earlier. The study has been published in the journal, Proceedings of the National Academy of Sciences.
Findings of the Study
The researchers did a detailed study of the ancient cratons (continental fragments), the continental fragments, in India, Australia, and South Africa. The researchers found the sandstones in Singhbhum with geological signatures of ancient river channels, tidal plains and beaches, aged over 3.2 billion years represent the earliest crust, exposed to air.
The scientists found a particular type of sedimentary rocks, called sandstones. They tried to find the age and the conditions in which they would have formed. For assessing the age of the sandstones, they analysed the uranium and lead contents of tiny minerals. The age of these deposits was estimated by studying microscopic grains of a mineral, called zircon preserved within these sandstones. They came to know that the rocks were formed in ancient rivers, beaches, and shallow seas which were 3.1 billion years old. This proved that all these water bodies could have existed only if there was continental land and led to the inference that Singhbhum was the first region which was above the ocean.
Patches of the earliest continental land of similar age also exist in the Pilbara Craton in Australia and the Kaapvaal Craton in South Africa. However, it is not known how much land was exposed at one time, and how long these landmasses remained above water.
As per the researchers, the granites, that form the continental crust of the Singhbhum region were formed due to extensive volcanic eruptions about 35–45 km deep inside the earth and continued at regular intervals for hundreds of millions of years. As a result, all the magma solidified to form a thick continental crust in the area 3.5 to 3.1 billion years ago. The hot plumes of magma beneath the crust caused portions of the craton to thicken and become enriched with buoyant, light weight materials like silica and quartz. Thus, became the craton ‘physically thick and chemically light’, as compared to the denser rocks surrounding it.
Formation of Early Life
The researchers are of the view that the earliest emergence of continental crust would have led to the formation of early life and weathering on land and nutrient run-off into the ocean. These nutrients might have helped early photosynthetic life flourish, leading to the production of oxygen and to the creation of rich atmosphere of the planet.
This study also found that the widely considered notion that plate-tectonics led to the emergence of the landmass did not hold true in this case, because plate-tectonics mechanism did not exist at that time.
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