Two unusual diamonds found deep inside the Earth are helping scientists answer a long-standing question about how our planet has remained suitable for life.
The discovery suggests that Earth has a natural way of keeping phosphorus, one of the most important elements for living things, close enough to the surface where life can use it.
The research was presented at the Goldschmidt 2026 Conference by a team led by Qiwei Zhang, a former Ph.D. student at the University of Alberta and now a postdoctoral researcher at the Carnegie Institution for Science.
Phosphorus is essential for life. It is a key part of DNA, which carries genetic information, and it also helps build cell membranes and store energy inside cells. Without enough phosphorus, life as we know it could not exist.
Scientists have known for many years that phosphorus moves between rocks, soil, oceans, and volcanoes near Earth’s surface.
However, they have wondered why plate tectonics—the movement of Earth’s giant crustal plates—has not carried most of this phosphorus deep into the planet’s mantle, where it would be trapped for billions of years.
The new study suggests that this rarely happens because the sinking oceanic plates are usually too hot. As they descend into the Earth, the heat causes phosphorus to escape before it can reach the deepest mantle.
This allows most phosphorus to stay in the upper parts of the planet, where it can eventually return to the surface and continue supporting life.
The evidence came from two “super-deep” diamonds. These rare diamonds formed between 410 and 700 kilometers below the Earth’s surface. Since humans have only drilled about 13 kilometers into the Earth, these diamonds act like tiny time capsules from places we cannot directly explore.
One diamond came from Brazil and is about 450 million years old. The other came from Canada’s Northwest Territories and is thought to be around 1.7 billion years old.
When Zhang examined tiny mineral inclusions trapped inside the diamonds, he expected to find common minerals. Instead, advanced testing revealed an extremely rare mineral called tuite. This mineral had previously been found only in meteorites that experienced enormous pressure after powerful impacts.
The discovery showed that phosphorus can sometimes travel as deep as 700 kilometers into the Earth. However, computer models revealed that this only happens under very unusual conditions. The sinking tectonic plate must remain much colder than normal. These rare “cold subduction zones” allow phosphorus to survive the journey into the deep mantle.
The diamonds also contained another high-pressure mineral called stishovite, confirming that they formed in these unusually cold environments.
The researchers believe these cold slabs also create a much denser type of rock, which changes how the tectonic plates move through the deep mantle.
The findings help explain why Earth has not lost most of its phosphorus over billions of years. By naturally keeping this life-supporting element close to the surface, our planet may have helped create and maintain the conditions needed for life to begin and continue.
Even tiny minerals locked inside ancient diamonds are now giving scientists a better understanding of Earth’s deep interior and its remarkable role in making life possible.
