We tend to lump New Zealand and Australia together. They're similar culturally and share the same geographical position, relative to North America and Europe, anyway. But according to a new paper published in the Geological Society of America Today, it looks like New Zealand and their neighbor New Caledonia are actually their own continent: 'Zealandia.'
Continent means something different to geographers and geologists. To be considered a geological continent, like Zealandia, the area in question has to satisfy a few conditions:
- the land in question has to be higher than the ocean floor
- it has to include a broad range of siliceous igneous, metamorphic, and sedimentary rocks
- it has to have thicker crust than the ocean floor that surrounds it
- it has to have well-defined limits, and be large enough to be considered a continent
In Geology, the first three points are well-understood. But as the authors say in the introduction to their paper, "...the last point—how "major" a piece of continental crust has to be to be called a continent—is almost never discussed... ." Since the Earth has so many micro-continents and continental fragments, defining how large something has to be to be called a continent is challenging. But the researchers did their homework.
They noted that the term "Zealandia" has been used before to describe New Zealand and surrounding regions. But the boundaries were never fully explored. 94% of this new continent is submerged, which helps explain why it's taken this long to be identified.
This map shows the spatial limits of Zealandia. Note the dotted red line that delineates continental crust from ocean crust. Zealandia is also bisected by a plate boundary between the Pacific Plate and the Australian Plate. Image: Mortimer et. al. 2017, GSA Today
Zealandia seemed to be a collection of broken pieces, but new data collected over the years has challenged that interpretation. Recent satellite data has given us new gravity and elevation maps of the seafloor. This data has shown that Zealandia is a unified region large as large as India.
"This is not a sudden discovery but a gradual realization; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper."
As the authors point out in their paper, it took a while to determine that Zealandia is a continent. There was no Eureka moment. "This is not a sudden discovery but a gradual realization; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper."
Besides satisfying our intellectual curiosity about our planet, the discovery is important for other reasons. A proper understanding of the plate structures and continental boundaries is important to other sciences, and may trigger further understandings that we can't predict yet. It may also point to other areas of research.
Also, many treaties rely on the agreed upon delineation of maritime and continental boundaries, including rights to fish stocks and underground resources. While the recognition of Zealandia seems clear from a scientific standpoint, it remains to be seen if it will be accepted politically.
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