Geological History

New Zealand The plants and animals endemic to New Zealand are quite unique in a number of ways. This is in large part due to the unique conditions here. Some niches filled by mammals on other continents are occupied by birds. Birds are predators and scavengers, some live on the ground or in burrows Our unique plants and animals are directly relate to our geological history.

Brief Geological History 200 million years ago, the land that was to become New Zealand, called Zealandia, was part of Gondwana. Zealandia lay between Southeast Australia and west Antarctica, most of it under the sea. About 100 mya there were flowering plants, deciduous trees, conifers, ferns, spiders, snails and the ancestors of native frogs and tuatara on the exposed surface of Zealandia. The early ancestors of mammals and snakes may have been present on Gondwana, but there is little evidence to suggest they were present on Zealandia at the time it broke away.

Brief Geological History 85 – 60 mya the Tasman Sea formed as a result of new sea- floor being created, splitting New Zealand from Australia and Antarctica. This prevented large animals from colonising Zealandia 25 – 30 mya, the Oligocene Bottleneck caused by rising sea levels and subsiding land masses, saw the extinction of many species living in New Zealand at the time. Surviving populations dropped to very low numbers as New Zealand only had 20% of its current land area exposed, mostly as isolated and scattered islands.

Brief Geological History Tectonic uplift and increased volcanism gradually resulted in more land becoming exposed and new habitats and niches forming. Approximately 10 mya New Zealand was a single, densely forested landmass. 5 mya the Southern Alps began to form, creating distinct geographic and climatic differences between the east and west coasts of the South Island. The Alps act as a barrier to circumpolar (westerly) airflow, creating wet rainforests to the west, and a dryer, warmer climate to the east.

Brief Geological History Accelerated uplift generated both upland and lowland environments, and wet and dry habitats, forming a mix of forrest, shrub-land, grasslands and alpine regions. Repeated glacial and interglacial cycles over the past 3 my caused large scale changes in sea level. Around 2 mya sea levels rose and the North and South Island became separated by Cook Strait. During the last major glacial period, 20 000 ya, sea level was about 100m lower than its present level, Therefore New Zealand’s land area was much larger.