This week, scientists made two interesting discoveries — first, that the Earth’s earliest continents rose out of the ocean 700 million years earlier than they believed; second, the first land to rise above the ocean about 3.2 billion years ago is in India.
Published this Monday in Proceedings of the National Academy of Sciences, a study by scientists from India, Australia, and the U.S. found the earliest crust exposed to the Earth’s atmosphere. How did they make this discovery? By analyzing sandstones from Jharkhand’s Singhbhum region, which was found to contain geological signatures of ancient river channels, tidal plains, and beaches that are more than 3 billion years old.
“The Singhbhum region is possibly Earth’s earliest continental land exposed to the air… Before that, Earth was a water world, the whole planet covered by water,” Priyadarshi Chowdhury, a geologist at Australia’s Monash University, who led the study, told The Telegraph. “This is the most direct, unambiguous date yet for the emergence of continental land.”
At present, the eastern region of Singhbhum is divided into three districts — East Singhbhum, West Singhbhum, and Saraikela Kharsawan — all of which are part of Jharkhand.
In course of the study, the researchers also attempted to understand what forced the Singhbhum landmass outside the ocean. “The sandstones tell us ‘when’ and the granite tells us ‘how,’” Chowdhury noted.
Interestingly, the findings in this regard, too, were eye-opening. The study didn’t just shatter our beliefs on when continental lands first rose. It found that contrary to previously held beliefs within the scientific community, plate tectonics didn’t contribute to the emergence of the landmass.
The chemical composition of rocks in the region contained information about the temperature and pressure at which they formed, allowing scientists to understand what transpired to have them emerge out of the water. “About 3.5 billion to 3.2 billion years ago, hot plumes of magma beneath the crust caused portions of the [landmass] to thicken and become enriched with buoyant, lightweight materials, like silica and quartz. This process left the craton ‘physically thick and chemically light,’ as compared to the denser rock surrounding it, and thus buoyed the landmass up and out of the water,” a report by LiveScience explained.
Chowdhury told The Guardian how the Singhbhum landmass was formed from an accumulation of lava. Over time, its crust became about 50 kilometers deep — “so thick [that] it just floats up above the water… like an iceberg floating on water.”