Story: Geological exploration
Page 6 – Plate tectonics and other advances
Before the late 1960s there was no unifying theory that explained the working of the earth and its surface features. Geology was mainly a descriptive, land-based science, and it was unclear how New Zealand was related to Australia and other countries of the Pacific.
Post-war exploration of the oceans provided a new view of the earth: the ocean floor is not as old as the continents. It lies on much younger volcanic rocks that have been ejected at mid-ocean ridges.
In the developing concept of plate tectonics, the surface of the earth was visualised as a mosaic of about 10 major crustal plates, moving independently but driven by convection currents deep within the earth.
Understanding the New Zealand region
The theory of plate tectonics was largely worked out and tested in the northern hemisphere. Understanding of the region around New Zealand had to await surveys of the sea floor, as well as the first deep- ocean drill holes in the region. A new picture became clear between 1969 and 1972.
The New Zealand region was originally on the margin of the Gondwana supercontinent, adjacent to Australia and Antarctica. New Zealand split away about 85 million years ago. Seafloor magnetic patterns show that the Tasman Sea gradually widened for about 25 million years, until spreading ceased about 60 million years ago.
New Zealand has been compared to an ark, sailing away from Australia with a cargo of Gondwana plants and animals – including ratite birds (the ancestors of moa and kiwi), tuatara and forests with kauri, podocarps and beeches. These then evolved in isolation. Plate tectonics revolutionised our understanding of why New Zealand plants and animals are unique.
About 25 million years ago a major fracture developed, and the largely submerged New Zealand region lay across the boundary between the Pacific and Australian plates. As the plates rotated, the opposite sides of the Alpine Fault started to move apart, and features that were originally adjacent are now separated by 480 kilometres. Earthquakes, volcanism and mountain uplift are all caused by New Zealand’s position across these two plates.
Earth science as a career
Until the 1960s there were few jobs for geologists in New Zealand, and many graduates worked overseas. The number of local earth science graduates has steadily increased, and they are now employed in petroleum, coal and mineral exploration as well as in engineering geology and environmental science.
Traditionally geology has been a white, male-dominated profession, and until the 1970s there was debate about the moral aspects of women doing field work alongside men. In 2006 there are now roughly equal numbers of men and women studying geology at undergraduate level. Few Māori have undertaken a career in earth science, and this had not changed at the beginning of the 21st century.
Research in New Zealand
Because of its range of natural features, New Zealand has been regarded internationally as a natural laboratory for geological study – from glaciation to volcanology and paleontology. The number of scientific papers and monographs published is much greater than would be expected from the size of the earth-science community. In a 2003 survey, earth science was rated third out of 41 disciplines taught at New Zealand universities for the quality and productivity of research.
In 1992 the Department of Scientific and Industrial Research (including the Geological Survey) was closed, and replaced by commercially focused crown research institutes. The Institute of Geological and Nuclear Sciences is responsible for land-based and some marine earth science, and a group from the National Institute of Water and Atmospheric Research studies offshore geology. Both organisations are involved in Ocean Survey 20/20, which aims for a comprehensive survey of New Zealand’s Exclusive Economic Zone by 2020.