Zealandia is a 4.9 million-square-kilometre expanse of continental crust that’s 94% underwater, with only New Zealand and New Caledonia sitting above the ocean’s surface. This is mostly as a result of crustal thinning before the super continental break-up,which can be seen using upgraded satellite-based elevation and gravity map technology.
Typically, Zealandia’s crust thickness ranges from 10 to 30km (6 to 19 miles) and is roughly the size of India. It’s believed to have broken off from Antarctica about 100 million years ago, and then again from Australia about 80 million years ago.
“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,” the researchers wrote.