Some 3.9 billion years ago, the entire planet was under water. The ground that emerged to become land was 12,000 meters down on the ocean floor. Then the continents rose, which scientists believed, up until now, started about 2.7 to 3 billion years ago.

A new discovery, however, has pushed back our known concepts of continent formation to 3.2 to 3.8 billion years ago.

An international team of geologists led by Indian scientist M. Santosh identified a 3.2-billion-year-old microcontinent that could have broken off from the landmass of what is now Madagascar or the African mainland.

The findings were reported in the Gondwana Research, an international journal that specializes in Earth science.

The discovery of the oldest microcontinent, the Coorg block, wedged into peninsular India, showed that peak continental building may have occurred around 3.1 billion years ago, said Santosh, first-author of the research article, now working at the China University of Geosciences and a recipient of the Talent Award under the 1,000 Talents Plan of the Chinese Government.

They also identified that rocks as old as 3.8 billion years are present in the basement of the 3,000-square-kilometer block.

"Ancient continental blocks floating over the globe in the past not only provide exciting candidates for understanding the formation of continents and supercontinents, but also offer general insights on the evolution of our planet," said Q.Y. Yang, co-author of the paper who also comes from the China University of Geosciences.

Previous research had also identified an old microcontinent in the Indian Ocean plate.

Studies, released in February, found remnants of an ancient microcontinent scattered under the ocean between Madagascar and India, dated at about 8.9 million years ago.

"Continents on our planet are the fundamental abode for human society, both for life and for resources. In the nearly 4.6 billion years of the Earth's history, when and how continents formed, and how the continental fragments amalgamated to form supercontinents are topics of general interest," Yang said.