Diamonds aren’t just a girl’s best friend – turns out they can be pretty useful to geologists too. In fact, as a new study found, some diamonds can even reveal secrets about the evolution of the Earth.
As the hardest known natural mineral, diamonds can and have survived a lot, including the creation and destruction of “supercontinents”. Buried deep beneath the surface of the Earth, researchers have analyzed diamonds that were formed millions of years ago under the supercontinent Gondwana.
These “superdeep” gems hold important clues as to the supercontinent’s formation, stabilization, and movement across the planet – aka the “supercontinent cycle”. This cycle, driven by plate tectonics pushing the crust below the Earth’s surface, can be otherwise difficult to study; the oceanic crust is young and the older, continental crust doesn’t provide much insight into deep geologic processes.
“Superdeep diamonds are extremely rare and we now know that they can tell us a lot about the whole process of continent formation,” explained study author Karen Smit in a statement. “We wanted to date these diamonds to try and understand how the earliest continents formed.”
Using a series of chemical analyses to identify and date tiny silicate and sulfide inclusions within the diamonds, including isotopic analysis, the researchers found that the diamonds formed between 650 to 450 million years ago, around 300 to 700 kilometers (186 to 435 miles) below the base of Gondwana. At this time, the supercontinent covered the South Pole.
As they were forming, the rocks they were within became buoyant and were transported alongside subducted mantle material to the base of the supercontinent, expanding it from below. And, as Smit explained, the diamonds have had quite the journey since.
“Around 120 million years ago, Gondwana started to break apart to form the present oceans such as the Atlantic. At 90 million years ago, the diamonds, carrying trapped tiny inclusions of the host rock, were brought to Earth’s surface in violent volcanic eruptions.”
These eruptions occurred in the fragments of Gondwana that we now know as Brazil and Western Africa. This, the researchers suggested, showed that the diamonds were “stuck” to the base, and so migrated with different fragments of the supercontinent as it split up.
Beneath their sparkly exterior, the study illustrates the importance of superdeep diamonds and research into continent formation. As Smit put it, “We need this type of research to understand how continents evolve and move. Without continents there wouldn’t be life. This research gives us insight into how continents form, and it links to how life evolved and what makes our planet, Earth, different from other planets.”
The study is published in Nature.