One of New Zealand’s most spectacular fossil sites originated 23.2 million years ago. It was formed in a valley dotted with small volcanoes, when rising magma deep below the Earth’s surface came into contact with groundwater. Lava and water don’t mix—they explode. The resulting detonation obliterated the surrounding forest and left a circular, low-rimmed volcanic crater, called a maar, about 3,000 feet across and more than 600 feet deep.
The prehistoric rains gradually filled in the hole, forming a lake. Eventually, the subtropical forest grew back, and year after year the trees dropped their leaves and flowers into its still waters. Microscopic algae called diatoms bloomed each spring and died at the end of summer, forming a fine, pale blanket on the lake bottom. In the autumn and winter, a darker layer of decaying plant matter and algal spores settled on top. Together, those alternating seasonal layers formed a barcode-like pattern in the stripy diatomite, recording each year of the maar’s long life.
Embalmed among the diatoms were the remains of other plants and animals that lived in or fell into the lake. In its depths, the enclosed, anoxic conditions kept every detail perfectly preserved: spiders, orchids, fruit, delicate flowers still dusted with pollen, and freshwater fish with their mouths gaping open.
Today, Foulden Maar, as it came to be known, is an unremarkable rectangle of heaped white earth located in the middle of a sheep pasture in the Strath Taieri, a broad river valley studded with rock outcrops in New Zealand’s far south. The Earth is now nine to 10 degrees Fahrenheit cooler than it was when the maar was formed, and the nearby mountains are shrouded in snow in winter, the dry fields bare of trees. And despite the riches lying beneath, Foulden Maar is currently off limits to scientists, the result of a protracted dispute with a company that wanted to mine the entire site for diatomite.
Starting in the early 2000s, geologists and miners had cooperated, allowing extraction to occur alongside scientific discovery. The fossils that were uncovered revealed an entire ecosystem of new species, and the diatomite layers provided a valuable high-resolution record of climate change during a time when the Antarctic ice sheets were rapidly melting. Scientists are still trying to unravel the causes of that deglaciation, as it may help to model Earth’s future.
The annual layers preserved in Foulden Maar form the only record that can “document this time period on human timescales—over periods of seasons to centuries,” says Beth Fox, a paleoclimatologist at the University of Huddersfield in the United Kingdom, who did her doctoral studies at Foulden Maar. “The scientific value of this deposit is very high.”
A new mining company, Plaman Resources, bought Foulden Maar in 2015. When Plaman’s ambitious plans for the site were revealed a few years later, researchers worried the fossils would all be crushed to dust, and it seemed the cooperative relationship between science and mining would end too. But New Zealanders rallied behind the fossils, and while Foulden Maar’s fate is still uncertain, it appears that public resistance may have saved the site for science.
Diatomite is globally abundant and is mined extensively in more than 20 countries. Its presence in the area around Foulden Maar was first described in 1875 by the geologist and naturalist Frederick Hutton, who called it “polishing powder.” Small-scale mining at the site began during World War II. Since then, the diatomite has been extracted, crushed into a substance more commonly known as diatomaceous earth, and used, variously, for polishing metals, filtering sugar, as insulation, for filtering beer and wine, as a cement and paint additive, as a mild abrasive, for making soaps, toothpaste, and face powder, and as an organic pesticide and fertilizer.
The diatomite at Foulden Maar—and the fossils embedded within it—didn’t initially make much of an impression on Daphne Lee, a geologist at the nearby University of Otago in Dunedin. Now 70, she first visited the site as an undergraduate student in the late 1960s or early 70s. In the 90s, she went again and collected a few crumbly leaf fossils. But no one recognized the site’s broader significance until 2003, when Lee was organizing a field trip for some visiting geologists.
One day she and some colleagues arrived for reconnaissance, and the miners working there had just opened up a 15-foot cliff face with a mechanical digger. One of Lee’s colleagues noticed the barcode-like layers of the algal blooms and realized the potential for climate research. The delineations between one year and the next would allow scientists to track changing conditions on an annual basis—a very unusual level of detail. As they poked around in the freshly exposed diatomite, Lee’s group found a few fossil leaves, pristine and perfect.
“It was really a lightbulb moment,” Lee says. “This place has got both fantastic preservation of leaves and this climate record.”
Jennifer Bannister, a fossil preparator at the university, mounted the 23-million-year-old leaves on slides. She did the same with some leaves from related species she picked in the botanical gardens, and they looked so similar that at first glance Lee had trouble telling the fresh and fossil specimens apart. The airless conditions had preserved the ancient veins, pores, and even some of the leaves’ chemistry.
In the early days, relations between the scientists and the miners were collegial. Alan Walker was the managing director of Featherston Resources, the mining company working the site back then. Walker, a former geologist himself, was intrigued by the finds. He was especially interested in the possibilities of the climate record. As the company explored the site, Walker alerted Lee’s team every time a new face was opened up. Without mining, Lee says, geologists would never have known about Foulden Maar’s riches at all. To show her appreciation, she even named a new species—a fossil fern—after Walker. (“I was really chuffed,” he says.)
A decade of discoveries and dozens of scientific papers followed. Lee and her colleagues received a series of prestigious grants that enabled them to spend a few stormy winter weeks in 2009 drilling a core 600 feet into the deposit below the snow-covered pasture. The diatomite layers continued for nearly 400 feet before giving way to volcanic rubble.
The core gave the scientists a continuous, high-resolution 120,000-year sequence of climate data from an epoch whose warmer temperatures provide a glimpse of what could be in store over the coming centuries. It also contained perfectly pickled leaves. By testing their chemistry and examining their pores under a microscope, one of Lee’s doctoral students, Tammo Reichgelt, was able to show that over the millennia preserved in the core, atmospheric carbon dioxide increased dramatically, then fell to levels similar to those predicted for later this century.
Reichgelt’s analysis of the leaves revealed that as CO2 levels increased, some plants could harvest that carbon more efficiently for photosynthesis, leading to increased growth and more tolerance for drought. That is not necessarily good news, though—Reichgelt says some studies indicate that while higher atmospheric CO2 might increase yields, the crops are less dense in nutrients, and any increased carbon storage will be still be far outpaced by fossil fuel emissions and deforestation.
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