The latest maps of the world's eighth continent - BBC Future - 0 views
-
in 2017, the story took an unexpected turn – the seven-continent model has been a mistake all along. Enter Zealandia, a long-lost land to the southeast of Australia, otherwise known as the planet's forgotten eighth continent. Scientists had long predicted the existence of this bonus southern landmass, but it remained missing for 375 years – largely because it’s almost entirely submerged under 1-2 km (0.6-1.2 miles) of water. Now they are beginning to unravel its secrets.
-
This month, an international team of researchers released the most detailed maps of Zealandia to date – incorporating all five million square kilometres (two million sq miles) of this underwater region and its geology. In the process, they have uncovered hints as to how this mysterious continent formed – and why it has been obscured beneath the waves for the last 25 million years.
-
Zealandia is thought to have formed around 83 million years ago, during the Late Cretaceous. However, its journey began up to 100 million years before that, when the supercontinent of Gondwana – which congealed much of today's land into one giant lump – started to break up. As it disintegrated, the world's smallest, thinnest and youngest continent struck out on its own, while the regions of Gondwana that had once laid directly to its north west and south west became Australia and Antarctica, respectively.
- ...8 more annotations...
-
It's thought that all or part of Zealandia may have existed as an island for a while. But then around 25 million years ago, it was disappeared beneath the ocean
-
The first real clues that New Zealand might represent just a tiny, visible portion of a vast incognito landmass came in 2002, when scientists used bathymetry – the study of the depth of bodies of water – to analyse the region. The ocean above what we now call Zealandia is considerably shallower than that surrounding it, suggesting that the area was not underlain by an oceanic tectonic plate – like most of the world's oceans – but a continental one.
-
The clincher came in 2017, when scientists put several lines of evidence together, including data about the kinds of rocks it contains and its relative thickness – oceanic plates tend to be thinner – to propose that this is indeed a new continent. This is not a mere continental fragment or microcontinent, as had previously been proposed, but the real deal, 95% of which is submerged underwater.
-
despite the excitement around the discovery of a new continent, and more than a decade of intensive research, many details of Zealandia's early formation have remained elusive. This is partly because of a strange event that occurred when it split from Gondwana.
-
In 2019, an international team of scientists mapped the geology of South Zealandia. Their research revealed that at some point, Zealandia had been stretched – pulled apart by tectonic forces, thinning the continent compared to regular continental plates and creating ruptures that later became oceanic crust. In the process, it became twisted and this made reconstructing its history to work out its original form much more challenging.
-
The researchers' analysis of rocks from the lost continent revealed that the stretching happened in two stages. The first began around 89-101 million years ago, and led to a rip which became the Tasman Sea inbetween Australia and New Zealand. The second phase started 80-90 million years ago and led to Zealandia splitting off from West Antarctica and creating the Pacific Ocea
-
For the latest study, another research group – involving many of the same geologists as before – charted North Zealandia. This time, they analysed rocks that had been dredged up from the Fairway Ridge, a region of the South Pacific off the coast of Australia, which forms the northernmost tip of Zealandia. These ancient remnants, which have not had a dry day for 25 million years, included a mixture of igneous rocks – those formed by volcanic processes – and sedimentary ones made in shallow basins just off the coast of Zealandia.
-
The resulting maps of Zealandia transform it from a featureless mass into a place with many bands of distinctive geology running along its length from northwest to southeast. These fit together with the geology of West Antarctica like a jigsaw puzzle, confirming that this region and Zealandia once slotted together.