Earth's seventh continent Zealandia was not always submerged, finds study

New Delhi: In February this year, scientists unearthed Earth's seventh continent, which they named 'Zealandia'.

Backed by satellite data and rock samples, scientists said that the 5 million square kilometer landmark located towards the east of Australia is a continent.

Zealandia, which is mostly submerged beneath the South Pacific, was once part of the Gondwana super-continent but broke away some 75 million-years-ago. Until now, the region has been sparsely surveyed and sampled.

Now, however, a study has found that Zealandia was not always hidden deep beneath the water as it is today.

Researchers affiliated with the International Ocean Discovery Programme (IODP) in the US in collaboration with scientists from 23 countries mounted a nine week expedition to explore Zealandia.

Expedition scientists drilled deep into the seabed at six sites in water depths of more than 4,101 feet.

They collected 8,202 feet of sediment cores from layers that record how the geography, volcanism and climate of Zealandia have changed over the last 70 million years.

Researchers found significant new fossil discoveries that prove Zealandia was not always as deep beneath the waves as it is today.

"More than 8,000 specimens were studied, and several hundred fossil species were identified," said Gerald Dickens of Rice University in the US.

"The discovery of microscopic shells of organisms that lived in warm shallow seas, and of spores and pollen from land plants, reveal that the geography and climate of Zealandia were dramatically different in the past," Dickens added.

The new discoveries show that the formation 40 to 50 million years ago of the "Pacific Ring of Fire," an active seafloor zone along the perimeter of the Pacific Ocean, caused dramatic changes in ocean depth and volcanic activity and buckled the seabed of Zealandia.

Researchers had believed that Zealandia was submerged when it separated from Australia and Antarctica about 80 million years ago.

"That is still probably accurate, but it is now clear that dramatic later events shaped the continent we explored on this voyage," said Rupert Sutherland of Victoria University of Wellington in New Zealand.

"Big geographic changes across northern Zealandia, which is about the same size as India, have implications for understanding questions such as how plants and animals dispersed and evolved in the South Pacific," Sutherland said.

The discovery of past land and shallow seas now provides an explanation. There were pathways for animals and plants to move along, researchers said.

(With PTI inputs)