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The story of Atlantis, a mythological continent that vanished into the sea after its inhabitants displeased the gods, has fascinated people for thousands of years. However, the idea of a whole continent sinking into the ocean may be more rooted in reality than you think.

Thumbnail image credit: Reto Stöckli

Hosted by: Michael Aranda

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Sources:
http://www.geosociety.org/gsatoday/archive/27/3/pdf/GSATG321A.1.pdf
https://www.britannica.com/place/Gondwana-supercontinent
https://geographic.org/geographic_names/name.php?uni=-237102&fid=6439&c=undersea_features
https://www.gns.cri.nz/Home/Learning/Science-Topics/Ocean-Floor/History-of-Zealandia
https://www.nature.com/articles/ngeo825
https://www.nature.com/articles/543179b?WT.feed_name=subjects_geology
https://www.gns.cri.nz/Home/Our-Science/Earth-Science/Regional-Geology/The-Geology-of-New-Zealand
https://books.google.com/books?id=g9ZogGs_fz8C
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2607375/
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Okay, look. I get that there are a bunch of great Disney movies, but Atlantis is arguably one of the best.

It’s got everything you need: great animation, some magic, a good story, and a city stuck at the bottom of the ocean. And it could even be real! Okay, so that last part isn’t totally accurate.

But some scientists do believe Earth has an eighth continent that, millions of years ago, sunk almost entirely underwater. It’s called Zealandia, and besides basically being real-life Atlantis, it also has a lot to teach us about geology. Zealandia makes up almost five million square kilometers of the southern Pacific ocean.

It includes New Zealand as well as regions to the south and north, all the way up to the island New Caledonia. Today, it’s almost totally underwater … but it wasn’t always. Millions of years ago, it was part of the supercontinent Gondwana, and was mashed together with other land masses including modern-day South America, Africa, Australia, and Antarctica.

It separated around 80 million years ago thanks to interactions between tectonic plates, the giant rock slabs that make up Earth’s surface. But it wasn’t exactly a clean break. As Zealandia pulled away, its crust began to stretch and thin, and it became less buoyant as a result.

At the same time, water began to fill the gap between it and Australia. As the crust got thinner and the sea got larger, that water began to cover Zealandia, too. And ultimately, it sank.

Unlike in Disney’s Atlantis, though, it didn’t happen in “a single day and night of misfortune.” It took millions of years. And it probably didn’t involve any super magical crystals, either. Still, around 55 million years after it separated, Zealandia was almost completely submerged.

And even though tectonic plate interactions have pushed some of it back above sea level, 94% of it is still under the ocean. The name Zealandia has actually existed since the mid-90s, but most geologists have just considered it a microcontinent, like India. That’s the label they use for areas made of continental crust but not large enough to be considered their own thing.

Over the years, though, researchers found more and more evidence to suggest Zealandia could be worth upgrading to proper continent status. And in a 2017 paper in the journal GSA Today, a team from New Zealand, New Caledonia, and Australia published the most compelling case yet for why we should just accept Zealandia as the Earth’s eighth continent. See, geologists typically consider continents to have four main qualities:.

First, they have to have a higher elevation compared to the oceanic crust around them. Second, they need to have a broad variety of rock types, including igneous, sedimentary, and metamorphic rock. For comparison, oceanic crust is typically only made of igneous rock like basalt.

Continental crust should also be less dense and thicker than oceanic crust. Typically, the continental stuff is 30 to 45 kilometers thick, while oceanic crust is only 7 kilometers. Finally, continents should have a well-defined, relatively large area.

There’s no set definition for what that exact area is, but it should be enough to distinguish it from things like continental fragments or microcontinents. These qualities all apply to the traditional continents. And according to this team, they apply to Zealandia, too.

Even though it’s mostly underwater, it’s still elevated compared to the oceanic crust around it. It also has a variety of rock types, and generally has the right thickness. It’s also more than twice as large as the next smallest microcontinent.

Most importantly, it’s also geologically distinct. It’s separated from Australia by a feature called the Cato Trough, which is almost four kilometers deep and considered a significant boundary. Not all geologists agree, though.

They have a bunch of reasons, but some suggest that it’s not a geologist’s job to figure out what a continent is in the first place — they’re there to study different kinds of crusts and features. Others have also made the case that since Zealandia is more like a bunch of different islands than one continuous landmass, it shouldn’t count. In response to this, the authors of the paper had a few words.

They said that if it weren’t for the, quote, “arbitrary datums of opaque liquid oceans,” we wouldn’t be having this discussion. In other words, if we studied Earth without its oceans — like we do for dry planets like Mars — it would be clear what Zealandia’s true identity is. We’d be able to see things like that difference in crust elevation more clearly, without all the water getting in the way.

But we’ll leave that fight to the geologists. If nothing else, though, researchers do seem to agree that Zealandia — whatever it is — can teach us a lot about the Earth’s crust. According to some models, Zealandia should’ve been ripped apart into microcontinents when it separated from Australia.

But instead, the crust just thinned out and sank — and so far, we’re not totally sure why. Figuring out how and why that happened could help us understand what else happened to the Earth in the past, as well as what might happen to modern continents in the future. While we’re figuring all of this out, though, one thing’s for sure.

If any Smithsonian researchers out there find a mysterious Atlantean treasure map ... you can give me a call. Or if you just want to create a treasure map of your own, check out this Skillshare class by Vancouver artist Tom Froese and learn how to illustrate creative maps using digital and analog tools. If you follow me on social media, you know that I trust my community a lot.

One thing I like about Tom, is that he’s the same way. This map making class was requested by his Instagram community and you can feel how thoughtful he’s been in designing the class with them in mind. Like a good map, he gives a great big picture overview, but pays special attention to the details as well.

And Skillshare is offering SciShow viewers 2 months of Skillshare for free right now. Click on the link in the description to sign up and check out Tom’s class or any of over 20,000 classes in art, business, technology, you name it. And if you make a map of Atlantis or Zealandia, let us know in the comments!

I want to see it! ♩.