You may believe you're familiar with all the continents, but have you heard of Zealandia?

In 2017, a previously unknown contingent of the shores of New Zealand was discovered - making headlines globally.

Zealandia, known as Te Riu-a-Māui in the Māori language, covers more than 5 million square kilometres, making it twice the size of the subcontinent of India.

You might be asking yourself why it wasn't uncovered earlier.

The explanation lies in the fact that 95 percent of its landmass is hidden beneath the southwest Pacific Ocean, having vanished long before the arrival of humans on the planet. What remains above water are primarily a significant mountain range (the two islands of New Zealand) along with a few smaller oceanic islands.

Not much information is available about the newly found continent, primarily because it is largely unreachable. Nevertheless, a group of geologists from various parts of the globe has created a fresh geological map that includes Zealandia. This map was developed through a blend of rock samples collected from the ocean and geophysical mapping techniques.

As geologists explored the outer edges of Zealandia in search of samples, they uncovered significant sandstone formations along with deposits of basaltic rock pebbles.

The sandstones are estimated to be approximately 95 million years old and include older granite and volcanic pebbles. This indicates that when Zealandia was above water, rivers originating from volcanic highlands deposited materials into tectonic basins.

The highlands were once a bustling volcanic range around 30 to 50 million years ago, but they probably underwent significant erosion during the time when the sandstone was laid down.

Geologists theorize that Zealandia experienced a gradual submersion approximately 40 million years ago, a conclusion supported by the finding of basalt pebbles linked to underwater volcanic activity.

The study "Reconnaissance basement geology and tectonics of North Zealandia" was published in the journal Tectonics(2023).