One continent nears recognition as another suffers annihilation

18 Feb 2017

Image: titoOnz/Shutterstock

February began with news of the Indian annihilation of a forgotten continent. Now, a New Zealand-based pretender to the continental throne is gaining momentum.

Zealandia, largely submerged in the Pacific Ocean, is not quite a continent – as yet, it is relatively unrecognised.

Beneath the surface, 94pc of Zealandia is largely unseen. A mere 6pc – made up of New Zealand’s north and south islands, as well as New Caledonia – is actual land, so to speak.

New neighbour

In a paper published last week in the Geological Society of America’s Journal, a team of researchers led by Nick Mortimer established that the wannabe continent measures 5m sq km – about two thirds of neighbouring Australia.

Roughly the same size as the Indian subcontinent, Zealandia is thought to have split from the old giant continent of Gondwana some time between 60-85m years ago.

“This is a big piece of ground we’re talking about, even if it is submerged,” said Mortimer, a New Zealand geologist, whose team is pushing for proper recognition of what would become the eighth continent.

Simplified map of Earth’s tectonic plates and continents, including Zealandia. Image: GSA

Simplified map of Earth’s tectonic plates and continents, including Zealandia. Image: GSA

Made up of a thick continental crust, its isolation from Australia is just one reason why Mortimer and a growing number of geologists think it should be considered a continent all to itself.

In addition, and in slightly more technical terminology, it has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure.

Plenty of fuss

Speaking to The Guardian, Mortimer said that although this is the first major paper dedicated to Zealandia, local geoscientists have been talking about the ‘new’ continent for years.

“They probably wonder what all the fuss is about,” he said, noting the release of a bathymetric map – a study of ocean floors – in 2002 as a pivotal moment.

“That’s when the penny dropped, really … From that point, that map was literally our roadmap for some crosses, just trying to get rocks out of all the four corners of Zealandia that we could, so we could prove up the geology.”

Should more scientists refer to Zealandia as a continent, should it be included in school books, for there is no official recognition of such things, then it will join Australia, Asia, Antarctica, Europe, Africa, North America and South America as the eighth continent.

Long gone

It will not join Mauritia, though, a similar Gondowana-deserter. Located under Mauritius, Mauritia was ripped apart when Africa and Eurasia split.

This continent then broke off from the island of Madagascar, when Africa, India, Australia and Antarctica split up to form the Indian Ocean of today.

In a paper published to Nature Communications, a team of South African, German and Norwegian researchers came to the conclusion of a lost continent when they discovered a mineral called zircon on the island of Mauritius.

Lost continent

Indian Ocean topography showing the location of Mauritius as part of a chain of progressively older volcanoes extending from the presently active hot spot of Réunion, towards the 65m-year-old Deccan Traps of north-west India. Image: Wits University

The discovery of zircon in any geological find would suggest ancient tectonic movements, but the age of the zircon discovered on Mauritius – estimated to be 3bn years old – is much higher than any other rock found on the island.

“Earth is made up of two parts: continents, which are old, and oceans, which are young,” said Wits University’s Prof Lewis Ashwal, author of the paper.

“On the continents, you find rocks that are over 4bn years old, but you find nothing like that in the oceans, as this is where new rocks are formed.

“The fact that we have found zircons of this age proves that there are much older crustal materials under Mauritius that could only have originated from a continent.”

A sorry end for one continent, a late bloom for another.

Gordon Hunt was a journalist with Silicon Republic