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Mining Rare-Earth Elements from…Fossilized Fish???

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In the western Pacific Ocean lies the tiny isle of Minami-tori-shima, the easternmost territory of Japan. The triangular speck covers only one square mile, and due to an odd wall-like perimeter, most of the island is strangely below sea level. There’s not much on it aside from an airstrip and a Japanese weather station. The nearest land is over 1,000 kilometers away.

Yet in spite of its inauspicious qualities, the island is the key to something extraordinary: a treasure trove of rare earth elements.

Just where that treasure is located is curiouser still. The lode is not on the island or in it. It lies in the clay sediment to the south of the seamount the island sits on, in a superdeposit of bits of fish teeth, scales and bone. The fish fossils are rare earth element traps.

There are so many of them and they have done their job so well that Japanese scientists have calculated that the mud in a 2,500-square-km zone south of this one tiny island could supply four of the world’s rare earth element needs for hundreds of years. But how? And why? And, most importantly, what do we do about it?

Rare earth elements are a set of chemical elements that occupy the broad gully of the periodic table. We are in the middle of a technology boom in which rare earth elements are vital to a bewildering array of machines. Many of them enable us to generate or capitalize on renewable energy.

Every time you purchase a TV, smartphone, LED, compact fluorescent bulb, or rechargeable battery; every time a utility erects a wind turbine; and every time Toyota builds a Prius, a spritz of rare earth elements is placed inside. Many medical and military technologies use them as well. As a result, consumption of the elements has increased in the past decade. Somewhat ironically, at the moment most of the mines from which they come are in China, with the attendant environmental woes.

Yet rare earth elements aren’t actually that rare on Earth. What is rare is finding these elements in a minable deposit. As a consequence of their chemical properties, they don’t often aggregate as rare earth minerals in such a way that they are easy to extract.

That’s where the fish come in. In a paper published this June in Scientific Reports, a team of Japanese scientists sought to date the fish fossils at Minami-tori-shima—and at a second similar site southeast of the Manihiki Plateau in the South Pacific—to determine their origin and whether there might be more elsewhere.

They used details of the fossils themselves and ratios of osmium isotopes in clay, whose abundance over time has been previously charted. They calculated that the fossils are 34.4 million years old, and their concentration at the foot of Minami-tori-shima is a fluke result of the planetary cooling that generated the Antarctic ice sheet.

Around 34 million years ago a permanent ice sheet began forming on Antarctica following a warm period. Shortly before (geologically speaking), the Southern Ocean finally flowed freely around the continent with the opening of the Drake Passage at the bottom of South America and of the South Tasman Rise, which replaced a land bridge between Tasmania and Antarctica. In concert with a decrease in atmospheric carbon dioxide, this circulation thermally isolated Antarctica from warmer air to the north and allowed it to grow colder, feeding ice formation.

As a result of the cooling, the Antarctic bottom water became colder and thus denser. Since denser water sinks, it began to flow north under warmer, less dense waters. This bottom water, which had been collecting and storing nutrients for millennia in the formerly sluggish southern sea, was stirred for the first time in a long time.

When this rich, cold water hit the base of seamounts large, steep and high enough, it was forced up. The influx of nutrients to sunlit water fed a bloom of life. Similar but less intense productivity boosts around seamounts caused by upwelling of deep currents exist today.

The resulting bonanza lasted about 100,000 years. When the nutrients stored around Antarctica ran out, it stopped. In the meantime, the grim but inevitable result—teeth, bone fragments and toothlike scales called denticles—sank to the bottom.

Bone is made of calcium and phosphate. And fossilized phosphate, it turns out, is really good at capturing rare earth elements, according to Junichiro Ohta, a study co-author. During the last 34 million years, the fossils slowly absorbed yttrium, europium, terbium, and dysprosium from the fluid trapped in the mud. The large surface area of bone bits enhanced that ability. As a result, the mud contains up to 20,000 parts per million of rare earth elements, although it is highly patchy. What makes the Minami-tori-shima deposit special is not that it contains fish fossils, or that the fossils are special in any way, it’s that a one-time process generated by past climate change resulted in a superdense deposit of them.

The Japanese team calculated that there are 16 million tons of rare earth oxides south of Minami-tori-shima—enough of the aforementioned four elements to supply the world for 420–780 years at current rates of consumption, and that the deposit “has the potential to supply these metals on a semi-infinite basis to the world.”

What this all implies, of course, is that Minami-tori-shima and Manihiki Plateau are by no means unique. Theoretically, any Pacific island or seamount sufficiently steep and high (with at least several thousand meters of rise) and in an ocean basin deep enough (calculated to be greater than 5,000 meters by the scientists) should point the way to a similar trove in a relatively small area near its base. The Pacific contains hundreds of islands and seamounts with suitable bathymetry, and a map of potential targets generated by the scientists is splotched with red.

The question, then, becomes what to do about it. Diversifying and massively increasing the planet’s supply of rare earth elements seems like a solid pro. An increase in resources means we can build more devices that replace the need for fossil fuels. And as the fish fossils are larger than the sediment they are entombed in, that makes their extraction a relatively simple matter of sorting by size, rather than applying toxic chemicals as with conventional surface mining. Compared to terrestrial rare earth sources, the mud also has low levels of radioactive elements like uranium and thorium.

But the fish fossils lie beneath over three miles of water, at a depth no commercial mining operation has yet been able to make profitable. And then there are the questions of the consequences of deep-sea mining.

Efforts to mine the seabed for the notorious manganese nodules that litter the oceans of the world (and that were infamously the pretext for the Glomar Explorer to attempt to raise a lost Soviet sub) are now proceeding for the actual purpose of mining manganese nodules in an area of the Pacific potentially as big as Spain.

In this case, the costs of disturbing the seabed of a such a large area are both likely underestimated and potentially high, according to a study published July 31 in Trends in Ecology & Evolution. The same misunderstandings are likely to plague calculations of the costs of all deep-sea mining projects, they argue.

One might make the argument that since the fish fossils are contained in relatively small area, the benefits of extracting them outweigh any biological costs. And yet, habitats immediately south of seamounts may be valuable biological real estate for many of the same reasons that put the fish fossils there in the first place. And, as humans are not omniscient, and the law of unintended consequences is ironclad, there may well be other unexpected costs.

How does all this weigh against the costs of continuing to obtain rare earth elements in China or through recent efforts to open new mines in the United States or elsewhere? A study published September 1 in Nature Communications discusses the very real possibility that threats to biodiversity created by surface mining for renewable energy technologies could exceed the good they do in stemming climate change if they are not planned and executed carefully. In short, it’s complicated.

Mining is not the enemy. Society cannot function without it. My father, a retired mining engineer, likes to say that every good you touch is either mined or farmed, and if you add in harvested (as with timber or fish), he is not wrong. Rather, just like agriculture or fisheries, how we go about mining is what matters. Unfortunately, that usually means higher prices.

Many people find it essential to get brand-new phones, computers or TVs on an annual or semi-annual basis without thinking twice, but with each purchase comes the consequences of obtaining the elements that make them work. This author lugged around an increasingly decrepit and highly mocked iPhone 4 from 2013 to 2020 for this very reason.

We must be wise in the conservation of resources, but also judicious in the selection and operation of new mines, whether on Earth’s surface or the ocean’s bottom. It is worth remembering the next time your cursor approaches the buy button for your next “must-have” device that its creation has consequences. And in the meantime, we should consider carefully the possibilities that a quirky windfall of past cooling present for preventing the dire consequences of our current warming predicament.

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