Aotearoa New Zealand, a land renowned for its breathtaking landscapes and unique biodiversity, also possesses a profound connection to “deep time” – an immense geological history stretching back millions of years. This ancient narrative is now being brought into sharper focus with the most comprehensive revision in two decades of the New Zealand Geological Timescale.
Much like the periodic table organises the elements, the geological timescale provides a framework for understanding Earth’s deep past. It meticulously measures the epochs and eras recorded in the very rocks that lie beneath our cities, towns, mountains, and rivers. As American writer Marcia Bjornerud aptly described it, the geological timescale is “one of the great intellectual achievements of humanity.”
For over a century, New Zealand’s geologists and palaeontologists have maintained their own distinct timescale. This is largely because the international version, predominantly developed in Europe and North America, has proven difficult to apply universally. A significant reason for this lies in the reliance on fossils to define most boundaries in deep time. Critically, many of New Zealand’s fossils, much like its living flora and fauna, are endemic, meaning they are found nowhere else on Earth. The recently revised New Zealand timescale addresses this by updating the ages of its divisions and resolving long-standing ambiguities in their definitions. This refinement promises to deepen our understanding of both the geological endowments and the inherent geohazards that characterise life on these “shaky isles.”
Stepping Beyond the Human Horizon
Deep time stands in stark contrast to the fleeting, short-term perspectives that often dictate political and economic cycles. To truly grasp the complexities of monumental shifts like climate change, mass extinction events, or the collapse of ice sheets – processes with profound implications for humanity spanning hundreds to thousands of years – we must transcend the limitations of immediate human experience. This broader temporal view is also crucial for comprehending natural hazards.
Consider the dramatic eruption of the Hunga Tonga–Hunga Haʻapai volcano in January 2022. While it may have appeared to unfold in a matter of minutes, this impression of brevity is deceptive. The formation of a volcano and its subsequent eruption are the culmination of processes that begin deep within the Earth, involving tectonic plate alignment, magma generation, and its slow ascent and evolution in subterranean chambers. These geological machinations can take hundreds of thousands, even millions, of years. Therefore, the Hunga Tonga–Hunga Haʻapai explosion, while seemingly instantaneous, was merely a fleeting moment in a narrative that commenced long before human habitation of the Pacific, perhaps even before the existence of humankind. Scientists use the geological timescale to quantify the pace of such events, and the precision of these measurements is paramount.
A Land Forged Over Millennia
The importance of an accurate geological timescale is underscored by significant findings from recent studies that have employed the previous New Zealand timescale to date key geological events and processes.
Volcanic Landscapes and Tectonic Drivers: A 2021 study meticulously mapped the extensive, yet largely concealed, volcanic system of Canterbury. This research identified and characterised 185 volcanoes that had erupted at various stages over the past 100 million years. The study revealed that these pulses of volcanic activity were intrinsically linked to major tectonic shifts, including the breakup of the supercontinent Gondwana and subsequent alterations in plate motion. This work demonstrated how New Zealand’s volcanism has been repeatedly shaped by deep, slow-moving plate tectonic forces, and how present-day landscapes can mask a dynamic geological past. The composition and arrangement of geological features like the Canterbury volcanic system are fundamental to the nation’s identity, influencing the distribution of both resources and hazards.
Shaping Modern Earthquake Hazards: Another recent investigation delved into how long-term tectonic processes continue to influence contemporary earthquake risks. Focusing on offshore regions east of the North Island, geologists examined the behaviour of rocks and fluids at the boundary where the Pacific Plate subducts beneath the Australian Plate at the seismically active Hikurangi Subduction Zone. Their modelling indicated that exceptionally high underground fluid pressures play a significant role in earthquake behaviour. These pressures, they suggest, are primarily driven by tectonic compression over the last three million years, rather than solely by the cumulative weight of overlying sediments. In essence, earthquakes in this region are a product of geological forces that have been accumulating for millions of years.
Reading the Past to Illuminate the Future
The significance of deep time extends equally to our understanding of life on Earth. Recent palaeontological discoveries have revealed that, as recently as three million years ago, close relatives of modern emperor penguins inhabited a subtropical climate in the New Zealand region. This finding challenges the prevailing assumption that these large penguins are confined to the icy coasts of Antarctica today due to some inescapable climatic destiny, suggesting instead that other factors significantly influence species distribution. Insights gleaned from the fossil record are thus indispensable for predicting how life and the geographical ranges of species may evolve in response to a warming climate and disturbances to Earth’s systems.
In separate research endeavours, scientists have reconstructed 100 million years of the geographical history of the largely submerged continent from which New Zealand emerges. These studies illustrate how the constant interplay of shifting landmasses, rising and subsiding terrain, and evolving coastlines have sculpted the iconic landscapes we observe today. Ultimately, deep time provides the essential context for understanding the origins of New Zealand’s unique flora and fauna. It shapes our approach to the sustainable management of vital resources and underpins our comprehension of geological hazards, guiding our efforts to mitigate their impact.
Collectively, these diverse studies highlight the critical importance of an accurate and up-to-date geological timescale. They also serve as a potent reminder that our actions today will resonate throughout the planet and affect future generations for hundreds of thousands of years to come.
