The land that would become New Zealand formed along the western coast of Gondwanaland throughout the Paleozoic Era. Beginning 500 million years ago and ending 100 million years ago, recurrent episodes of deposition, compression and uplift added this land to the great Southern Continent. Then, about 85 million years ago, future New Zealand was torn from Gondwanaland as the Tasman Sea began to open, triggering the Island's long period of isolation.
From 55 to 25 million years ago, the ocean gradually opened between Australia and Antarctica; this process increased tectonic forces in New Zealand, which lies along the boundary of the Australian and Pacific Plates. The North Island sits above the edge of the Australian plate; subduction of the Pacific Plate below the Australian Plate in this area has produced volcanism across the North Island. New Zealand's South Island, on the other hand, straddles the two plates and the prominant Alpine Fault marks the boundary; compression east of the fault forced up the Southern Alps while the western side of the Island creeps northeastward along the fault. South of the South Island, the Pacific Plate subducts beneath the Australian once again. There is certainly no mystery why New Zealand is prone to earthquakes!
Since New Zealand rifted into isolation 85 million years ago (a time when Tyrannosaurus rex ruled the land), its only native terrestrial mammals have been bats, which flew in more than 30 million years later; neither has it ever been home to snakes, which evolved after the rift occured. Indeed, New Zealand's native fauna has been limited to invertebrates, fish, amphibians, lizards, birds, bats and marine mammals (pinnipeds, whales and dolphins). Since they had no land predators, some of the birds became flightless, represented today by the kiwi and kakapo (a flightless parrot). Polynesian explorers finally arrived in 800 AD, making New Zealand the last land mass (other than Antarctica) to be colonized by man; bringing in dogs and rats, the Mauri soon altered the flora and fauna forever!
