Wednesday, February 15, 2017

Lost Continent of Zealandia Found

Most of us view the continents and oceans as discrete entities of land and water across Earth’s surface. However, even a cursory look at our world establishes the problem. 

Are North America and South America truly separate continents with their connection through the Isthmus of Panama? Where and why does one distinguish Europe, Africa, and Asia considering the Bosphorus and Sinai Peninsula? One might suggest a geological reason: Continents are large, identifiable areas underlain by continental crust. 

The article by Nick Mortimer, Hamish J. Campbell, Andy J. Tulloch, Peter R. King, Vaughan M. Stagpoole, Ray A. Wood, Mark S. Rattenbury, Rupert Sutherland, Chris J. Adams, Julien Collot, and Maria Seton follows this idea, but then throws a fascinating twist on the subject: Zealandia. 

Zealandia was formerly part of Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup. Earth’s surface is divided into two types of crust, continental and oceanic, and into 14 major tectonic plates.

Simplified map of Earth’s tectonic plates and continents, including Zealandia. Continental shelf areas shown in pale colors. Large igneous province (LIP) submarine plateaus shown by blue dashed lines: v

Zealandia once made up ~5% of the area of Gondwana. The study authors write: "The importance of Zealandia is not so much that there is now a case for a formerly little-known continent, but that, by virtue of its being thinned and submerged, but not shredded into microcontinents, it is a new and useful continental end member. Zealandia started to separate from Gondwana in the Late Cretaceous as an ~4000-km-long ribbon continent "

Zealand though 94% submerged remains unbroken. It is the 7th largest continent as is the "size of approximately the area of greater India."

One only needs to look at a bathymetric map, where ocean water is removed, to appreciate the issue. 

Several islands, notably New Zealand and New Caledonia, are connected by submerged continental crust across a large area of Earth's surface. This mostly underwater continent is geologically separate and distinct from Australia and Antarctica, and as highlighted by Mortimer and colleagues, should be treated as such. Basically, from a well-reasoned geoscience perspective, 

Credit: NIWA

Earth has well-established continents, but also an extra one, mostly underwater. "Zealandia illustrates that the large and the obvious in natural science can be overlooked," conclude the authors.

Contacts and sources:
U.S. Geological Society

Citation: Zealandia: Earth’s Hidden ContinentNick Mortimer et al., GSA Today, v. 27, doi: 10.1130/GSATG321A.1.

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