Land has existed in the vicinity of New Zealand for most of the last 500 million years: the earliest rocks found in the country are thought to have originated in the continental forelands of Australia and Antarctica, part of Gondwanaland, the massive continent to which New Zealand belonged. The oceanic islands were created by continental drift, the movement of the large plates that form the earth's crust, which created a distinct island arc and oceanic trench about 100 million years ago.

Roughly 26 million years ago, the land that makes up New Zealand rose further from the sea, and the landscape you see today was formed by volcanic activity and continuous movement along fault lines, particularly the Alpine Fault of the South Island. The essential geology of the two islands is different: the North Island is at the edge of two tectonic plates, where one has slid beneath the other, resulting in prolific volcanic activity; the South Island is the site of two tectonic plates crashing into each other, causing rapid mountain building. Today New Zealand experiences about four hundred earthquakes every year, roughly a quarter of them strong enough to be noticeable. The volcanoes on the North Island, some still impressively active (the last eruption was Ruapehu in 1996), extend from the Bay of Plenty to the dormant volcanic cone of Mount Taranaki on the West Coast.

Isolated from man and other mammals, New Zealand would have been the perfect place to study the evolution of species. It's hardly surprising that so many botanists considered the oceanic islands as laboratories where they could perfect their theories. The country was separated from all other land masses for so long that, uniquely, birds occupied the position in the food chain usually held by mammals. Darwinism would suggest that with no predators the birds became fearless, learning to walk amid the dense bush, gradually becoming flightless and growing in size. If allowed to develop unhindered, perhaps they would have evolved into a serious competitor to mammals, but their perfect adaptation to the environment brought their downfall with the arrival of man and other aggressive, fast-moving mammals.

No ground-based mammals colonized the islands until Maori gave rats and dogs passage in their canoes, possibly in about 1000 AD although some theories suggest earlier. Maori were also responsible for hunting the large, flightless moa into extinction, and clearing great swathes of bush with fire. At that time both islands were almost entirely covered in dense forest composed of over a hundred species of tree, the floor carpeted by moss and lichen with a thick tangled undergrowth of tree fern, some species over ten metres high. Amongst the trees and ferns were twining creepers, nikau palms and palm lilies, all intermingled and forming an impenetrable bush alive with native birds.

The changes to the land brought by Maori pale in comparison with the incursions of the Europeans. Right from Cook's first exploratory visits, when he brought with him the pig, the sheep and the potato, Europeans tampered with the delicate balance of New Zealand in an attempt to turn it into a "New England". In the early 1800s whalers and sealers bloodied the coastal waters, while logging campaigns cleared vast swathes of native trees, leaving land suitable only for grazing cattle; later, gold prospectors diverted streams and carved chunks out of hillsides. Perhaps the greatest environmental changes were made by immigrant farmers, who had introduced over fifty species of mammal to New Zealand by the start of World War I, including rabbits, weasels, mountain goats, cats, dogs, frogs, mice, possums and wallabies. These animals decimated native animal and plant life in the increasing competition for food. Imported plants, such as blackberry, pine and gorse, had just as much effect: allowed to grow wild, they choked and destroyed hundreds of unique plants vital to the ecology of the islands.