The discovery of super-deep diamonds, formed at astonishing depths between 410 and 700 kilometres below the Earth's surface, has revealed a fascinating interplay between the planet's geological processes and the very building blocks of life. This finding not only challenges our understanding of Earth's role in preserving life but also sheds light on the intricate dance between shifting continents and the cycling of phosphorus, a vital component of DNA and cell membranes.
One of the most intriguing aspects of this discovery is the revelation that under normal conditions, the descending slabs of oceanic plates, which drive plate tectonics, are too hot to allow the deep Earth to permanently sequester phosphorus. This means that billions of years of plate tectonics have not locked away phosphorus in the deepest recesses of the Earth's mantle, which is a mystery that has long puzzled scientists. The study, led by former University of Alberta PhD student Qiwei Zhang, now a post-doctoral fellow at the Carnegie Institution for Science, alongside researchers Dr. Graham Pearson and Dr. Thomas Stachel, has provided a compelling explanation for this enigma.
Zhang's research, which involved analyzing two super-deep diamonds, one from Brazil and the other from Canada's Northwest Territories, has revealed the presence of tuite, an ultra-rare mineral that is a high-pressure transformation of apatite, the most common phosphate mineral found in Earth's crust. The discovery of tuite inside these diamonds proves that phosphorus can occasionally travel to the lower mantle, but Zhang's modelling shows that this deep cycling is incredibly inefficient, requiring an extraordinarily rare environmental anomaly known as a 'cool' subduction zone.
What makes this discovery particularly fascinating is the realization that when a tectonic slab is cold enough to preserve phosphorus, the extreme environment forces the descending plate to transform into an entirely new, highly dense mantle rock type. This unique density and structure likely dictate how deeply cold slabs can penetrate into the lower mantle, which has implications for our understanding of planetary evolution. The research also carries weight for the diamond industry, as super-deep diamonds account for 90 per cent of the world's largest and most valuable gems, including the legendary Cullinan diamonds embedded in the British Crown Jewels.
From my perspective, this discovery raises a deeper question about the delicate balance between the Earth's geological processes and the preservation of life. It also highlights the importance of understanding the deep Earth to better comprehend what's happening on the surface. As Zhang notes, 'We try to better understand the deep Earth to help us better understand what’s happening on the surface.' This discovery not only provides new insights into the cycling of phosphorus but also offers a fresh perspective on the origin of life and the intricate relationship between the Earth's geological processes and the building blocks of life.
