A SA TAXI whisked me into Townsville in tropical north Queensland, my eyes were drawn to the tallest object on the skyline: a drilling derrick, seemingly out of place in the harbour.

I soon recognised it as part of the JOIDES Resolution, a oneof-a-kind research ship equipped to drill deep into the ocean f loor and take core samples. This was the very ship that was shortly to take 30 scientists, including me, on a nine-week scientif ic expedition to probe the secrets of the newly named eighth continent of ‘Zealandia’.

This extraordinary event is the f irst time a new continent has been discovered since January 1820, when a Russian expedition, led by naval officers Fabian Gottlieb von Bellingshausen and Mikhail Lazarev, battled treacherous seas to reach an ice shelf along the coastline of Antarctica. In doing so, they became the f irst people ever to set eyes on the frozen southern realm.

Less dramatic, but perhaps more surprising, was the announcement by scientists in 2017 that Earth had an eighth modern-day continent. This one sank beneath the waves 85–60 million years ago and was originally bigger than the Indian subcontinent of today. The only vestiges of this land mass that remain above the ocean are New Zealand, New Caledonia and the Australian administered Norfolk Island.

Unknown to geologists, as much as 94 per cent of this continent – Earth’s smallest in the modern sense, with an area of continental crust covering 4.9 million sq.km of the Pacific – had been hidden right beneath our noses.

While the name Zealandia was first used in 1995, it was the gradual accumulation of data gathered during several decades, including satellite imagery and gravity and depth maps of the ocean f loor, that ultimately led a group of scientists in New Zealand, New Caledonia and Australia to publish a paper in March 2017 in the journal GSA Today, off icially declaring it a new continent.

It was this discovery and the ongoing work to understand Zealandia that, several months later, saw me leave my home in the USA, where I am a professor of geology at the City University of New York, to join the expedition departing from Townsville during the Australian winter of 2017.

As part of the International Ocean Discovery Program (IODP) expedition aboard the JOIDES Resolution, our goal was ambitious. We would drill ocean f loor cores from multiple locations on or near Zealandia, recovering sediments from more than 850m below the surface that were laid down as much as 68 million years ago. We aimed to reconstruct a picture of the climate and geology of this lost continent, going all the way back to the age of the dinosaurs.

SEEING THE 62m-high derrick of the 143m-long JOIDES Resolution brought back memories of my previous two expeditions on this mighty research vessel: on the f irst, we explored the region south of Tasmania, and on the second we traversed the icy waters off Antarctica. This time, I was to be an on-ship sedimentologist, one of a team of 30 scientists from a dozen different countries who had all been chosen to take part. Together, we made up IODP Expedition 371, tasked with exploring and understanding the history of Zealandia.

The IODP is among the most successful of international science programs. It has evolved over decades, gathering increasingly comprehensive records on climatic and oceanographic changes during the past 100 million years by collecting hundreds of kilometres of sediment cores from every ocean f loor all around the world.

The work of the IODP is the pre-eminent source of information for data older than 800,000 years, which is beyond what we can learn from ice cores extracted from the planet’s great frozen expanses.

With 80 crew members and drillers on board, as well as the scientists, we left Townsville on 27 July 2017 for our f irst drill site, more than 2100km east of Australia. We planned to work at six different drilling locations spread over a wide area, penetrating deep below the sea f loor after extending pipes down through ocean depths of up to 4.5km.

My research would focus on developing climate and oceanographic records from prehistoric times when levels of carbon dioxide (CO2) in the atmosphere were higher than they are today – information vital for understanding the threat we face from climate change today and into the future.

Levels of CO2 in our atmosphere have already risen from 280ppm (parts per million) before the industrial revolution to more than 400ppm today – and are predicted to rise to more than 500ppm before the end of the century.

The work of palaeoclimatologists has revealed that the last time the levels of CO2 in our atmosphere were as high as 500ppm was more than 25 million years ago. To achieve atmospheric levels of CO2 equal to those that humanity has

managed in a mere two centuries, Mother Nature needed tens of millions of years.

In a sense, looking at the climate with this amount of greenhouse gas in the atmosphere allows us to use the past to look ‘back to the future’. These data are going to prove increasingly valuable as we head further into climatic conditions far beyond anything previously experienced by our human species.

ASIDE FROM CLIMATE, we hoped to learn much more about the geolog y and geography of mysterious Zealandia. Only about 6 per cent of it remains above sea level – the largest pieces being New Zealand and New Caledonia. The rest of the continent lies on average more than 1km beneath the waves.

It has taken decades of painstaking underwater research using seismic data (information from sound waves) to capture images of the sediment and rock layers below the sea f loor, as well as take core and dredge samples, to determine the true extent of this vast submerged landmass.

The combined picture of this data has revealed Zealandia to have all the characteristics of a continent, including the fact that its low-density, silica-rich rocks (characteristic of continental crust) are signif icantly elevated above the surrounding sea f loor of the oceanic crust.

Zealandia has an amazing history. Like Australia, it was once part of the southern supercontinent Gondwana – accounting for about 5 per cent of it – before breaking away from Australia and Antarctica about 80 million years ago. It then sank below the waves, qualifying it as a kind of a dinosaur-era Atlantis. However, the real mysteries occurred after this. Data suggest it began to rise once more, before disappearing under the waves for good (or at least until now). The timing and extent of its previous re-emergence is an area of hot debate.

Furthermore, without knowing its prehistoric geography, scientists can only guess at what effects Zealandia might have had on ocean circulation and planetary climate. Indeed, when we look back to this region more than 25 million years ago, when CO2 levels were above 500ppm, there is a signif icant discrepancy between temperatures estimated by climatic models and those hinted at by data from rocks and sediments.

Understanding this confusion is important because these are the same kinds of climate models we’re using now to predict our climatic future in a rapidly warming world. While much data has already been collected on the geology and geography of the long-submerged rocks of Zealandia, on this expedition we were collecting deep-sea cores of sediment capable of giving us a wealth of detailed information and unlocking the history of this mysterious continent.

SIX DAYS IN, and we’d reached our f irst exploration site. Drilling starts by lowering a pipe through a hole in the ship’s hull called the moon pool. The pipe typically extends down through thousands of metres of water. Once it reaches the sea f loor, a special coring bit drills in and recovers 9m of core sample at time. The core sample is pulled back up through the pipe to the ship where it’s carried by half-a-dozen science technicians to a row of tables. Here, they cut it into 1.5m lengths, determine the age of each and then subject the sections to a barrage of tests – sensors detect natural gamma rays, density, magnetic susceptibility, thermal conductivity and much more.

These records will ultimately provide the data needed to understand the climate and geological history of this landmass many tens of millions of years ago when parts of it were above the surface and populated by prehistoric creatures.

At this f irst drill site, we were in for a big surprise. We drilled 300m below the sea f loor to study a baff ling feature revealed by seismic data that had led to wild speculation. Excitement built as we drilled closer to the feature, f irst reaching a sediment layer that turned out to be 40 million years old and had been deposited in shallow water.

Immediately below we found volcanic rocks that formed when Zealandia had risen up. The volcanic layers were geochemically altered by ancient sea water, resulting in the most beautiful coloured rocks. These were dated to a time when, elsewhere on the planet, early primates were swinging through trees and great hornless rhino-like creatures had reached the size of dinosaurs.

We were all thrilled, because now we had ages and waterdepth estimates for when some of these rock layers were deposited, which we could apply to layers elsewhere, helping us to start building a geological map of this part of Zealandia. This was supposed to be among the least interesting of the drill sites and yet here we were celebrating exciting new discoveries.

After this f irst surprise, it was on to our next three drill sites, each located on the slopes of deep-water basins in Zealandia. The second two were further east, one directly south of New Caledonia and the other directly north of New Zealand, with the fourth site located between New Zealand and Australia.

The history of each of these regions of Zealandia had been shrouded in mystery around when they first subsided and if

Looking at the climate with this amount of greenhouse gas in the atmosphere allows us to use the past to look ‘back to the future’.

they had ever risen above sea level again. At the two eastern sites we recovered sediments up to 50 million years old, from a time when Earth was much warmer than today, due in part to high CO2 levels. At the site between Australia and New Zealand, we recovered sediments dated to 67 million years ago, when dinosaurs still roamed the planet and very shortly before their demise in a mass extinction.

The sediments extracted from all three sites bore evidence of the tremendous power of nature. Gravity had generated ancient underwater avalanches that scoured the sea bottom as they rumbled down from shallower waters into the abyss of these deep tectonic depressions.

Most of the sediments were composed of microscopic shells formed by single-celled planktonic creatures known as foraminifera. These have been around since creatures first began building shells more than 500 million years ago. They live within sea-f loor sediments as well as f loating in the upper few hundred metres of the ocean and create fantastically intricate shells. It seems incredible that single-celled creatures each less than half a millimetre across can form such beautiful and varied designs. Some are in the shape of a whorl, like a snail, while others are more abstract geometric styles.

Foraminifera are also incredibly useful for scientists who study past climatic and oceanic changes, because they reveal clues to prehistoric water temperature, acidity, CO2 levels, ocean productivity, and volume of ice at the poles.

MANY WEEKS INTO our nine-week journey, at the second and fourth drilling sites, we saw twisted layers on the ocean f loor that were evidence of massive blocks of sediments that had slid down the tilted slopes deeper into the abyss.

The repeated folding of individual sedimentary layers resulted in a great chaos of rock – an anarchy of strata, where sedimentary beds repeated. To add further confusion to this cacophony of sediments, we also found evidence of volcanoes, because these undersea avalanches contained rock that originated deep within the Earth. In the remote past, somewhere on Zealandia, volcanic mountains belched f ire.

While the actual volcanoes no longer exist – and therefore their exact location is hidden – we found volcanic debris in many of our sediment cores spanning a period of 20 million years at the second and third drilling sites.

With these cores, we were able to determine ages and water depths for the f irst time in each of the basins we drilled, as well as revealing the size and scope of the ancient avalanches, earthquakes and volcanic eruptions. For the f irst time, we were reconstructing the prehistoric geology and geography of this mysterious continent.

Our sixth and f inal site was off the continent itself, in deeper waters that plunge down to more than 4.8km, between Australia and Zealandia.

Though our time was limited, we collected cores from great depths that are helping us understand why there appeared to be folding of the rock layers, despite the fact it was seemingly far from tectonic activity. Geological quirks had resulted in the sediments being bright colours, and they sometimes contained exotic pink minerals that delighted our eyes after eight weeks out at sea. But by then our adventure was almost over.

FINALLY, THE JOIDES RESOLUTION sailed into Hobart on 26 September. An amazing expedition had ended, with the science team having bonded in a way that only happens when you are mutually gripped by the magic of exploration and discovery. Our f irst evening in port was f illed with celebratory drinking and eating as well as a few tears over our impending departure.

We have since returned to our respective nations and academic institutions to work on the thousands of samples collected. I have students studying samples from 17–15 million years ago, when CO2 levels in the atmosphere were higher than today, as well as 15–7 million years ago, when levels were more like those in recent pre-industrial times. However, the bulk of our work will focus on mapping out the geology and geography of Zealandia over time. Preliminary results seem to conf irm a hypothesis that the continent rose up dramatically between 55 and 34 million years ago.

But we have also come to realise that the prehistoric geography of Zealandia can’t be inferred simply by looking at its shape today. The next step is to integrate all the different kinds of data to model how the continent has changed over the past 65 million years.

As a result of the expedition, we eventually plan to create high-resolution oceanographic and climatic records for those 65 million years. The goal for us is to rewrite the tectonic, geographic, climatic and oceanic history of this new continent.

While the expedition of a lifetime may be over, the real scientif ic adventure is about to begin as the researchers and academics of Expedition 371 begin deciphering the many secrets of the lost continent of Zealandia.

For the first time, we were reconstructing the prehistoric geology and geography of this mysterious continent.