By Aditi Girish Kallanagoudar | Contributor
A study has found that Earth’s continents first emerged from oceans millions of years earlier than thought.
Although it has been widely debated, geologists largely believed that the creation of continents began about 2.5 billion years ago due to the interactions of tectonic plates, a process known as plate tectonics.
A recent study of ancient rocks in continental fragments of India, Australia and South Africa has revealed that the oldest known pieces of the continents began to form nearly 3.3 to 3.2 billion years ago, soon after Earth itself formed, and 700 million years earlier than what most models predict. The new findings reveal more about how the Earth’s earliest continents – or cratons – emerged from the primitive ocean that covered the earth.
The research team, which includes Priyadarshi Chowdhury from Monash University in Australia, assessed igneous and sedimentary records of the Indian Singhbhum Craton from 3.6 billion to 2.8 billion years ago with a particular focus to the zircon grains in the Singhbhum sandstones.
In their analysis, they found that these grains were deposited around 3 billion years ago, which not only makes them some of the oldest beach deposits in the world, but also implies that the Singhbhum Craton in eastern India first rose above the ocean around 3.3 billion to 3.2 billion years ago, much earlier than previous estimates of 2.5 billion years ago.
The scientists noted that sedimentary rocks of about this age are also present in the Pilbara and Yilgarn cratons of Australia and the Kaapvaal Craton of South Africa, indicating that continental landmasses may have emerged during this period not just in India, but around the globe.
Though it had been theorized that continental material built up along the boundaries of tectonic plates during the subduction of the oceanic crust and magma under the earth’s primitive ocean, this study found that these plate tectonics were not essential to the rise of the earliest continent from the ocean.
It was found instead that the emergence of Singhbhum Craton from the ocean was influenced by the thickening of volcanic magma under the ocean. This magma which was buoyant due to its silica-rich composition floated on top of Earth’s mantle.
The emergence of this continental crust not only contributed to the emergence of early life on land, but also contributed to the weathering and nutrient runoff into the ocean which helped early photosynthetic life flourish that ultimately created the oxygen rich atmosphere we currently live in.Science and Technology