The cratons, planet Earth’s first continents, arose from the seas between 3.3 and 3.2 billion years ago, a new study has suggested – several hundred million years before what was previously believed.
Findings from a new study show that the whole Singhbhum Craton (eastern India) became subaerial around 3.2 to 3.3 billion years ago. The researchers examined rocks for tiny crystals – zircons – which contain uranium in order to date them.
Once the team had calculated the breakdown of the uranium, they arrived at the conclusion that the craton had emerged “over 700 million years earlier than most models predict.”
According to the authors of the paper published on Monday in the journal Proceedings of the National Academy of Sciences (PNAS), “when and how Earth’s earliest continents — the cratons — first emerged above the oceans (i.e., emersion) remains uncertain.”
Understanding the timeline and the first formation of continental crust is important, the scientists stressed, “as it likely played a critical role in establishing Earth’s habitability.”
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The scientists examined igneous and sedimentary rock from the craton. The lead author of the research, Dr Priyadarshi Chowdhury of Monash University, remarked that the rocks must have formed on land because of features like ripple markings – similar to the patterns wind and waves leave on sandy beaches.
After creating a model to mimic the conditions which formed the rocks and propelled them out of the ocean, the team hinted that hot magma beneath the Earth’s crust caused parts of the craton to thicken. The matter also became buoyant with lightweight materials, such as sicilia and quartz, which brought it out of the water.
“There was no uncertainty that continents were partly sticking out of water as early as 3.4 billion years ago,” Ilya Bindeman, a geology professor at the University of Oregon, told Live Science.
Similar geographical incidences have also been observed in cratons in South Africa and Australia, which the scientists said suggests several landmasses could have appeared on the planet in this period.
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