Continents rose above oceans earlier than thought

New York

Continents may have first risen above the oceans about 3 billion years ago - a billion years earlier than thought, a new study has found.

To shed light on the origins of continents, isotope geochemist Bruno Dhuime at the University of Bristol in UK and colleagues analysed more than 13,000 samples of rocks from the continental crust.

Some of these samples were more than 4 billion years old.

Previous research suggested the first 2 billion years of Earth's 4.5-billion-year history were dominated by volcanic activity that generated the kind of crust now seen on the seafloor, 'Live Science' reported.

Continent-like crust, which is thick and rich in silica, was thought to only have emerged in great volumes in the past 2 billion years.

However, the new research found that modern, silica-rich continental crust first appeared about 3 billion years ago.

The thick, buoyant nature of these chunks of crust would have made them rise high above what became the seafloor, researchers said.

"Continents certainly existed early in Earth's history, but perhaps many were submerged," said geologist Cin-Ty Lee at Rice University in Houston.

Earth is the only known planet whose surface is divided into continents and oceans. Currently, the continents rise an average of about 4 kilometres above the seafloor, researchers said.

The study was published in the journal Nature Geoscience. -PTI