Бразилийн эрэг орчмын далайн ёроолд олдсон чулуужсан акулын шүднүүд нь батерейны үйлдвэрлэлд шаардлагатай ховор металлуудыг өөртөө хэрхэн хуримтлуулж буйг судлаачид тогтоожээ.
Бразил болон олон улсын судлаачдын баг Scientific Reports сэтгүүлд нийтлүүлсэн судалгаагаараа Рио Гранде далайн өндөрлөгөөс олдсон акулын шүднүүдийг шинжилсэн байна. Эдгээр шүдний дотоод бүтэц дэх хүний үснээс ч нарийн сувгууд нь төмөр болон манганы исэл бүхий эрдэс давхарга үүсэх таатай орчин болдог аж. Уг процесс нь шүдний биоапатит эрдэс задрахаас эхлээд манганы исэл ялгарах хүртэл дөрвөн үе шаттайгаар явагдаж, эцэст нь лити болон никель агуулсан литиофорит эрдсийг бий болгодог байна.
Судлаачид Sirius синхротрон хурдасгуурын тусламжтайгаар хийсэн нарийвчилсан шинжилгээгээр никелийн агууламж нэг грамм тутамд 37,000 микрограмм хүртэл буюу жингийнх нь 4 орчим хувийг эзэлж байгааг тогтоожээ. Рио Гранде өндөрлөг нь өмнө нь халуун орны ой мод бүхий арал байсан бөгөөд өдгөө далайн ёроолын энэхүү бүс нутаг нь кобальт, никель, лити зэрэг чухал эрдэс баялгийн нөөц бүхий бүс болсон байна.
Тус багийнхан акулын шүдийг далайн ёроолын металл бүрхүүл үүсэх эхний шатны процессыг харуулах бичил загвар гэж үзэж байгаа юм. Судалгаанд ашигласан шүднүүдийн геологийн нас болон зүйлийг нарийвчлан тодорхойлоогүй ч, 2012 онд тус бүсээс олдсон мегалодон акулын шүд нь эртний аварга загас амьдарч байсныг гэрчилдэг. Энэхүү нээлт нь дэлхийн далай тэнгисийн ёроолд чухал металлууд хэрхэн ялгарч, хуримтлагддаг болохыг ойлгоход шинэ гарц нээж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
On a drowned plateau about 1,000 kilometers off the coast of Brazil, fossil shark teeth lie in the seafloor sediment, slowly turning black. The dark color comes from a crust of iron and manganese oxides that grows on them over millions of years. Inside those teeth, Brazilian and international researchers have now traced, step by step, how the metal-rich minerals take hold.
The work, published in Scientific Reports, shows that the process starts deep inside the tooth, in channels thinner than a human hair. It ends with a manganese mineral loaded with lithium and nickel, two of the metals most in demand for batteries.
The team, led by Thales C. Felipe of the Oceanographic Institute of the University of São Paulo, worked with scientists from Roma Tre University in Italy, Harvard University, Central Michigan University and the Geological Survey of Canada. The nickel concentration they measured in one mineral phase reached about 37,000 micrograms per gram, close to 4% of its weight.
A Sunken Island the Size of Spain
The teeth come from the Rio Grande Rise, the largest oceanic plateau in the South Atlantic. It lifts the seafloor from about 4,000 meters deep to less than 1,000 meters, and its summit reaches about 600 meters below the surface. The plateau stretches for nearly 1,500 kilometers.
It was not always underwater. In 2023, a team including Luigi Jovane, a professor at the same Oceanographic Institute and a co-author of the new study, found red clay on the plateau typical of tropical volcanic soils, showing that the rise was once a forested tropical island before it sank.
Today, its slopes are covered with ferromanganese crusts, dark mineral layers that build up on rock at a rate of millimeters per million years. These crusts are rich in cobalt, nickel, copper, lithium, tellurium and rare earth elements. Brazil’s geological survey signed exploration contracts for them with the International Seabed Authority, and since 2018 Brazil has asked a United Nations commission to recognize the plateau as part of its extended continental shelf.
Shark teeth are a common find in these crusts. In 2012, a dredge haul by the Geological Survey of Brazil brought up a tooth embedded in a crust, later identified as belonging to a megalodon, the giant extinct shark. It was the first such record offshore in the South Atlantic.
The Metal Grows Inside Channels in the Dentine
Shark teeth are made of bioapatite, a calcium phosphate mineral, and their inner layer, the dentine, is crossed by microscopic tubes. After a shark dies and its teeth settle on the seafloor, those tubes become a sheltered space where seawater, microbes and dissolved metals meet. The researchers examined the teeth with a range of instruments, from micro-CT scans to electron microscopes and laser analysis, to map what grew there and in what order.
They identified four stages. First, the bioapatite of the tooth begins to break down and its organic matter decays, possibly with the help of microorganisms that bore into hard material. Second, nanoscale particles of goethite, an iron oxide, settle on the walls of the dentine tubes.
In the third stage, manganese oxidizes and forms lithiophorite, a layered manganese oxide that grows over the goethite. This is where lithium and nickel concentrate, with lithium at about 650 micrograms per gram and nickel at about 37,000. In the fourth stage, rare earth elements and yttrium move into the altered bioapatite, while cerium stays mainly with the oxides, before clay finally fills the remaining space.
X-Rays From a Brazilian Synchrotron
To measure the chemical state of the iron and manganese, the team used X-ray absorption spectroscopy at the Sirius synchrotron, a particle accelerator in Campinas, Brazil, that produces extremely bright X-rays. The data came from its Carnaúba beamline, designed to analyze materials at the scale of billionths of a meter.
The measurements showed that the iron in the tube walls is goethite, and that the manganese in lithiophorite has an average oxidation state of about 3.6, a mix of two forms of manganese. That detail is what allows the mineral to hold lithium and nickel within its layered structure.
The authors present the teeth as a microscale model of what happens in the first stages of ferromanganese crust and nodule formation. These crusts and nodules are among the largest reservoirs of critical metals on Earth, and the study offers a way to see how metals are sorted between minerals right at the start of the process.
A Taxonomist Sorted the Teeth First
Before any of the chemistry could start, the teeth had to be identified. A specialist from the Federal University of Pernambuco examined the samples to determine which sharks they came from. The published summary of the paper does not list the species or the geological age of the teeth.
The megalodon tooth recovered from the same plateau in 2012 measures 57.1 millimeters high and was dredged from a depth of 664 to 667 meters, its cutting edges worn smooth by the sea.
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