Delving into ‘deep time’: what NZ’s ancient past reveals about its present

We know Aotearoa New Zealand is home to many geographically and biologically special features. Yet few of us know it also has its very own measure of “deep time”.

Known as the New Zealand Geological Timescale, it has just undergone its most comprehensive revision in 20 years.

Like the periodic table, the geological timescale brings order to Earth’s deep history, measuring millions of years of time recorded in the rocks beneath our planet’s cities and towns, mountains and rivers.

It has been described by American writer Marcia Bjornerud as “one of the great intellectual achievements of humanity”.

For more than a century, New Zealand geologists and palaeontologists have maintained their own scale because the international timescale, developed largely in Europe and North America, has been difficult to apply elsewhere.

Even today, most boundaries in deep time are defined using fossils. Most New Zealand fossils, as with our living plants and animals, are found nowhere else.

The revised New Zealand version updates the ages of the timescale’s divisions and removes many long-standing ambiguities in how they are defined.

As a result, it will improve our understanding of both the geological gifts and the geohazards of life on the “shaky isles”.

Looking beyond the human timescale

In one sense, deep time is the antithesis of the short-term view that drives political and economic cycles.

To properly understand climate change, mass extinction or ice-sheet collapse – processes that carry profound implications for humanity hundreds to thousands of years from now – we need to step beyond the limited perspective of direct human experience.

This is also important for how we think about natural hazards.

The explosive eruption of the Hunga Tonga–Hunga Haʻapai volcano in January 2022, for instance, seemed to unfold over just a few minutes. But that impression of brevity can be misleading.

For a volcano to erupt, tectonic plates must first align and magma must form deep within the Earth, rise toward the surface and evolve in underground chambers before any lava is finally released – a process that takes hundreds of thousands to millions of years.

Consequently, the Hunga Tonga–Hunga Haʻapai explosion was only a fleeting moment in a story that began long before humans settled in the Pacific, possibly before humans existed at all.

As scientists, we measure the pace of such processes using the geological timescale – and we want those measurements to be as precise as possible.

A land millions of years in the making

Why is this so important? Consider some major findings from recent studies that utilised the previous New Zealand timescale to determine the ages and rates of key events and processes.

One 2021 study mapped the widespread but largely buried volcanic system of Canterbury, characterising 185 volcanoes that have erupted at various stages over the past 100 million years.

These pulses of volcanism were shown to align with major tectonic events, including the breakup of the supercontinent Gondwana and later changes in tectonic plate motion.

The study showed how volcanic activity in New Zealand has repeatedly been shaped by deep, slow-moving plate-tectonic processes – and how present-day landscapes and seascapes can conceal a dynamic geological past.

Geological elements such as the Canterbury volcanic system are the basic building blocks of our island nation; the composition, arrangement and properties of such elements determine the distribution of resources and hazards within New Zealand.

Another recent study explored how long-term tectonic processes continue to shape modern earthquake hazards.

Focusing offshore from the eastern North Island, geologists examined how rocks and fluids behave along the boundary where the Pacific Plate is being forced beneath the Australian Plate at the seismically active Hikurangi Subduction Zone.

Their modelling suggests that unusually high underground fluid pressures can strongly influence how earthquakes behave, and that these pressures are driven mainly by tectonic squeezing over the past three million years, rather than simply by the weight of sediments piling up.

In other words, earthquakes in this region are shaped by geological processes that have been building for millions of years.

Measuring the past to understand our future

Deep time is equally important for understanding life on Earth.

Recent discoveries in the fossil record show that, three million years ago, close relatives of modern emperor penguins were living in a subtropical climate in the New Zealand region.

This finding challenges the assumption that these large penguins are forced to live along the icy coasts of Antarctica today by some climatic inevitability, and suggests other factors play a decisive role in shaping where species live.

Such understanding from the fossil record is key to predicting how life and species distributions might change in response to warming climate and disturbances to Earth systems.

In further separate studies, researchers reconstructed 100 million years of geographic history of the largely submerged continent from which our home, New Zealand, emerges.

Their studies show how shifting landmasses, rising and sinking terrain and changing coastlines have shaped the iconic landscapes we see today.

Ultimately, deep time helps explain the origins of New Zealand’s distinctive plants and animals.

It frames how we think about using – and sustainably managing – the resources we depend on. And it underpins our understanding of geological hazards and what we can do to mitigate them.

Taken together, all of these studies show why having an accurate, up-to-date geological timescale matters – and why our actions today will affect the planet and our descendants for hundreds of thousands of years to come.