Probing the hidden continent of Zealandia

Ocean floor rock cores drilled into the sunken continent of Zealandia are revolutionising our understanding of Earth's history and how continents form.

Ocean floor rock cores drilled into the sunken continent of Zealandia are revolutionising our understanding of Earth's geological history and how continents form.

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Zealandia might be a hidden continent, but it is twice as large as India. It surrounds New Zealand and stretches north to New Caledonia and south beyond subantarctic Campbell Island.

Professor Rupert Sutherland, from Victoria University of Wellington, says "it was really discovered in the 1960s and 1970s through seafloor mapping." In 1972, three rock cores were drilled into the seafloor, revealing rocks that were continental in nature.

But despite its size it is a newcomer in being recognised as a continent. It was formally recognised, scientifically in 2017, having already been acknowledged legally under the United Nations Convention on the Law of the Sea.

Unlike the world's other continents, which are mostly above water or covered in shallow water, nearly 95 percent of Zealandia is underwater, at depths of a kilometre or more.

"What makes New Zealand different is that so much of it is underwater," says Professor Gerald Dickens, from Rice University in the United States.

In 2017, for the first time in nearly 50 years, an International Ocean Discovery Programme expedition aboard the JOIDES Resolution drilled at six carefully chosen sites to gather evidence that could answer questions about how Zealandia formed and also how other continents formed.

It has been known for a few decades that New Zealand began separating from Australia and Antarctica, which were all part of the ancient continent of Gondwana, about 100 million years ago. This separation stopped about 50 million years ago.

'That's where the history of Zealandia gets truly fascinating," says Gerald.

"It starts going through compression and uplift, so parts of Zealandia are going up and parts are going down, and it becomes a very complicated continent."

Rupert says that what is becoming clear is that these upheavals between 50 and 20 million years ago were in some way related to the Pacific Ring of Fire.

The Ring of Fire is related to the process of subduction, a process where a tectonic plate "subsides and sinks deep into the earth's mantle," says Rupert. The result is an active zone of volcanism and tectonic activity…

Go to this episode on rnz.co.nz for more details