Zealandia
via Futurism:
In a new study published in the journal Tectonics, researchers announced that they've finished mapping out most of the two million square miles of Zealandia, Earth's mostly-submerged eighth continent that mainly breaks the surface as the island of New Zealand...The prevailing theory about how Zealandia came to be submerged, which the GNS Science team affirms, posits that as the former supercontinent of Gondwana stretched out, its tectonic plates began to crack and allow ocean water in. After Antarctica later broke off, the crust of Zealandia continued to thin out until it became submerged -- and lost to the depths.