A new study reveals how Zealandia was formed

Mapa topográfico de Zealandia. Wikicommons
Mapa topográfico de Zealandia. Wikicommons

In 2017, the scientific community described Zealandia as a new continent almost completely submerged under the waters of the Pacific Ocean. It presents a landmass that extends from north-eastern Australia to beyond southern New Zealand. Its extension could be about two thirds the size of the Australian continent.

Zealandia is a very unusual continent since it is practically submerged underwater and only its highest mountains, New Zealand and New Caledonia emerge. For the moment being, there is no consensus on the definition of the continent. While some refer to Zealandia as 'the eighth continent', others say it would be the seventh one, following Africa, Eurasia, North America, South America, Antarctica and Australia.

Its existence was already known in 1972, when a scientific expedition recovered several samples of the ocean floor in the area, but it was not until 2017 that a team dedicated itself to explore it in-depth as part of the International Ocean Discovery Program (IODP).

Since then, scientists have been studying thousands of microfossils obtained in several perforations of its seabed and some of the results have been published in the journal Geology. As revealed in the article, the continent emerged from two tectonic events. In the first place, it was separated from Australia and Antarctica 80 million years ago. Later on, the same forces that initiated the formation of the Pacific Ring of Fire, an area of ​​volcanoes and earthquakes located on the shores of the ocean, also affected Zealandia.

"The results of these studies have changed what little was known about this hidden continent," explains Laia Alegret, a palaeontologist at the University of Zaragoza and one of the authors of the work.

“They have allowed us to know how it evolved as an independent continent after separating from Australia and Antarctica 80 million years ago. How the depth of its seas changed over time and when it emerged and sank, conditioning the migrations of the species, ocean currents and the global climate.

“In addition, it has been possible to specify the movement of tectonic plates, which seems to be related to the formation of the Pacific Ring of Fire. These results provide information on climate change and on fundamental geological processes, with implications in the prevention of geological risks such as volcanoes or earthquakes.”

Zealandia and the Ring of Fire

The authors of this new work have found evidence that suggests that Zealandia was not always a submerged continent since some of its regions rose above sea level for between 50 and 35 million years. Subsequently, practically the entire continent ended up sinking at least one kilometre.

The processes that shaped Zealandia have a lot to do with the Pacific Ring of Fire, a region with intense seismic and volcanic activity. Although there is no detailed information regarding its formation, it is known that it resulted from subduction processes, which occur when a tectonic plate sinks underground. Apparently, about 50 million years ago a subduction breakdown event spread throughout the entire western Pacific.

“What is suggested is that the process was similar to a massive super slow earthquake that resurrected old subduction failures that had remained dormant for millions of years, but began to move again,” notes a press release published by the University Institute of Research into Environmental Sciences of Aragon.

“There is probably no current analogue of this process, but the evidence from Zealandia suggests that these events can dramatically alter the geography of the continents. This same event created natural resources, affected the global climate and changed the direction and speed of movement of almost all the tectonic plates of the planet. It really was an event of global significance.”

The team of scientists continues working on the analysis of all the samples collected during the expedition, so new information will be discovered on this fascinating and unknown continent.

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