Evrim Yazgin
Cosmos science journalist
A new review brings together all the geological research that has been done on the ancient underwater continent known as Zealandia.
Zealandia, or Te Riu-a-Māui in the Māori language, only pokes above the surface of the waves in the islands of New Zealand (Aotearoa) and New Caledonia. What is known about the ancient continent is largely based on onshore geological studies and offshore mapping.
All the available information was brought together in the research published in the New Zealand Journal of Geology and Geophysics.
Despite being hidden under the waves for millions of years, Zealandia is the youngest continent on Earth. It was once part of the prehistoric supercontinent Gondwana which included other southern continents and subcontinents Australia, India, South America, Africa, Antarctica and Madagascar.
Gondwana began splitting about 180 million years ago (mya). Zealandia remained attached to Australia until about 80 mya when it began to “unzip” due to the movement of the tectonic plates. It had completely separated by about 55 mya.
“This is the most comprehensive review yet of the geology of the five million square kilometre, 95% submerged, Zealandia continent,” says the review’s sole author Nick Mortimer, a geologist at the Institute of Geological and Nuclear Sciences – a publicly owned New Zealand research organisation.
The majority of Zealandia’s land today is in Aotearoa’s North and South Islands.
“Since its maximum drowning 25 million years ago, movements at plate boundaries have built up the North and South Islands,” Mortimer says. “I’ve had a 4-decade research career, and it’s only recently that we have gathered much of the evidence defining Zealandia as a continent.
“While I hope this review will be a useful reference for at least the next decade, there are more discoveries to come. We’ve answered a lot of the ‘what’, ‘when’ and ‘how’ questions but many ‘whys’ are still unknown, such as: why did the Gondwana supercontinent break up? and why are there so many extinct volcanoes scattered across Zealandia?”
James Crampton, a palaeontology and geology professor at Te Herenga Waka Victoria University of Wellington in New Zealand, was not involved in the review but stresses its importance as a baseline in understanding the unique development of the submerged Zealandia continent and its island remnants.
“Zealandia’s stratigraphic archive records the history of planet-driving ocean-climate systems and of unique plants and animals – Aotearoa’s living taonga,” Crampton says. “Importantly, Zealandian strata document the causes and regional impacts of perturbations on the Earth system – natural experiments that reveal the responses of our life, oceans and climate to disturbances of varied scale, cause and rate. The geological record of Zealandia is a globally critical piece in the Earth system puzzle.
“The paper by Mortimer is a succinct but rich and beautifully illustrated summary of everything we know about our continent. There is so much more to learn; it is the responsibility of New Zealand scientists to unveil our piece of the Earth system puzzle and place it into the global context; this task is urgent.”
