Researchers from Monash University claim that the first continents on Earth must have emerged from the oceans 3.3-3.2 billion years ago, which is 700 million years earlier. than previously thought.
They examined the sedimentary and igneous rocks found in the Singhbhum Craton, an ancient continental fragment in India, and discovered evidence of eroding continental masses that date back 3 billion years ago. Analysis showed that the base of the creation indicates the continental crust began thickening about 3.5 billion years ago.
Analysis of the 3-Billion-Year-Old Beach
In the study, titled "Magmatic Thickening of Crust in Non-Plate Tectonic Settings Initiated the Subaerial Rise of Earth's First Continents 3.3 to 3.2 Billion Years Ago" published in the journal Proceedings of the National Academy of Sciences, researchers analyzed sandstone deposition the Singhbhum Craton believed to be once ancient rivers, estuaries, and beaches.
Daily Mail reported that the team looked at the micro grains of a mineral called zircon that naturally contains tiny amounts of uranium that decay to lead over geological periods of time. This made it possible for the team to determine the time when zircon crystals were formed on the beach.
Based on their uranium-lead dating, they discovered that ancient sediments in the creation were deposited about 3 billion years ago. Researchers noted that these sediments were by far the oldest they have known.
More so, this means that the presence of beaches at this time shows that a landmass must have emerged in the part where India is now located by at least 3 billion years ago to prove their theory.
Researchers wrote that sedimentary rocks of almost the same age were found in the oldest cratons of Australia, namely the Pilbara and Yilgarn cratons, as well as the Kaapvaak Craton in South Africa. They added that this discovery suggests that about 3 billion years ago, multiple landmasses must have emerged from the ocean.
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The Rise of Earth's First Continents
In an article the researchers wrote in The Conversation, they explained that the continents rise above the oceans due to their thick, buoyant crust that allows them to float on top of Earth's mantle. Just like icebergs, thick crust sticks above the water compared to thinner crusts that remain submerged.
They explained that ancient continents, such as the cratons, were formed through the melting of pre-existing rocks at the base of the crust. The study showed that granites in the Singhbhum Craton formed at greater depths at least 3 billion years ago, which implies that the crust was thicker during that time.
Furthermore, researchers said that the ancient crust of the creation would have become progressively more buoyant as it grew thicker over time because granites are one of the least dense types of rocks. They estimated that its thickness must have grown up to 50km. which makes it buoyant enough to begin rising at sea level.
The rise of Earth's first continents has significantly influenced the atmosphere, climate, and oceans of the ancient Earth. On the other hand, its erosion would have provided the chemicals needed for coastal environments in which early photosynthetic life was starting to thrive that led to the boom of oxygen production followed by the oxygen-rich atmosphere and then life as we know it today.
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