But there are still many unknowns. The unusual origins of the eighth continent make it particularly intriguing to geologists, and more than a little baffling. For example, it's still not clear how Zealandia managed to stay together when it's so thin and not disintegrate into tiny micro-continents. Another mystery is exactly when Zealandia ended up underwater – and whether it has ever, in fact, consisted of dry land. The parts that are currently above sea level are ridges that formed as the Pacific and Australian tectonic plates crumpled together. Tulloch says opinion is split as to whether it was always submerged apart from a few small islands, or once entirely dry land. This also raises the question of what lived there. With its mild climate and 39 million-sq-mile (101 million-sq-km) range, Gondwana itself was home to a vast array of flora and fauna, including the first four-limbed land animals and later, an abundance of the largest to ever live – the titanosaurs. So, could the rocks of Zealandia be studded with their preserved remains? A debate about dinosaurs Fossilised land animals are rare in the southern hemisphere, but the remains of several were found in New Zealand in the 1990s, including the rib bone of a giant, long-tailed, long-necked dinosaur (a sauropod), a beaky herbivorous dinosaur (a hypsilophodont) and an armoured dinosaur (an ankylosaur). Then in 2006, the foot bone of a large carnivore, possibly a kind of allosaur, was discovered in the Chatham Islands, about 500 miles (800km) east of the South Island. Crucially, the fossils all date to after the continent of Zealandia split from Gondwana. However, this doesn't necessarily mean there were dinosaurs roaming over the majority of Zealandia – these islands may have been sanctuaries while the rest was drowned, as it is now. "There's a long debate about this, about whether it's possible to have land animals without continuous land – and whether without it, they would have been snuffed out," says Rupert Sutherland, a Professor of Geophysics and Tectonics at the Victoria University of Wellington. The plot thickens with one of New Zealand's weirdest and most beloved inhabitants, the kiwi – a dumpy, flightless bird with whiskers and hair-like feathers. Oddly, its closest relative is not thought to be the Moa, which is part of the same group – the ratites – and lived on the same island until its extinction 500 years ago, but the even-more giant elephant bird, which stalked the forests of Madagascar until as recently as 800 years ago. The finding has led scientists to believe that both birds evolved from a common ancestor that lived on Gondwana. It took 130 million years to fully break up, but when it did, it left behind fragments which have since been scattered all across the globe, forming South America, Africa, Madagascar, Antarctica, Australia, the Arabian Peninsula, the Indian Subcontinent, and Zealandia. This, in turn, suggests that at least part of now-submerged Zealandia has remained above sea level the whole time. Except around 25 million years ago the entire continent – even possibly the entirety of New Zealand – is thought to have been plunged underwater. "It was thought that all the plants and animals must have colonised afterwards," says Sutherland. So what happened? [caption id="attachment_28208" align="alignnone" width="906"] Satellite data can be used to visualise the continent of Zealandia, which appears as a pale blue upside-down triangle to the east of Australia (Credit: GNS Science)[/caption] When the continent was finally unveiled to the world, it unlocked one of the most sizeable maritime territories in the world. "It is kind of cool," says Mortimer, "If you think about it, every continent on the planet has different countries on it, [but] there are only three territories on Zealandia." In addition to New Zealand, the continent encompasses the island of New Caledonia – a French colony famous for its dazzling lagoons – and the tiny Australian territories of Lord Howe Island and Ball's Pyramid. The latter was described by one 18th-Century explorer as appearing "not to be larger than a boat." A mysterious stretching Zealandia was originally part of the ancient supercontinent of Gondwana, which was formed about 550 million years ago and essentially lumped together all the land in the southern hemisphere. It occupied a corner on the eastern side, where it bordered several others, including half of West Antarctica and all of eastern Australia. Then around 105 million years ago, "due to a process which we don't completely understand yet, Zealandia started to be pulled away", says Tulloch. Continental crust is usually around 40km deep – significantly thicker than oceanic crust, which tends to be around 10km. As it was strained, Zealandia ended up being stretched so much that its crust now only extends 20km (12.4 miles) down. Eventually, the wafter-thin continent sank – though not quite to the level of normal oceanic crust – and disappeared under the sea. Despite being thin and submerged, geologists know that Zealandia is a continent because of the kinds of rocks found there. Continental crust tends to be made up of igneous, metamorphic and sedimentary rocks – like granite, schist and limestone, while the ocean floor is usually just made of igneous ones such as basalt.