JOHANNESBURG, South Africa — Ancient diamonds from hundreds of millions of years ago are revealing a hidden chapter in the Earth’s history. The diamonds, formed between 450 and 650 million years ago within the heart of the supercontinent Gondwana and unearthed from mines in Brazil and Western Africa, are shedding light on the complex processes that shaped continents and set the stage for the early evolution of life on our planet.
Scientists from the University of Witwatersrand in South Africa are offering a fresh perspective on the formation, stabilization, and movement of supercontinents like Gondwana during Earth’s distant past.
“Superdeep diamonds are extremely rare and we now know that they can tell us a lot about the whole process of continent formation,” says Dr. Karen Smit, of the Wits School of Geosciences, in a university release. “We wanted to date these diamonds to try and understand how the earliest continents formed.”
These diamonds, formed millions to billions of years ago, possess the unique ability to illuminate the deepest and oldest realms of the Earth’s mantle. Continents continuously shift across the Earth’s surface, occasionally converging to create “supercontinents” before breaking apart again — a phenomenon referred to as the “supercontinent cycle.” Diamonds, among the toughest minerals, endure these ancient cycles of creation and destruction, preserving their history within.
One of the complexities of studying deep geologic processes, especially in Earth’s ancient past, is the limited view provided by the relatively young oceanic crust and continental crust. However, old diamonds provide a direct window into the deep workings of Earth, including how they relate to the supercontinent cycle.
To date the diamonds and trace the addition of material to the keel of the supercontinent, the research team, led by Dr. Suzette Timmerman of the University of Bern in Switzerland, analyzed tiny silicate and sulfide inclusions inside the diamonds. This meticulous analysis led to the discovery of a previously unknown geological process.
“The geochemical analyses and dating of inclusions in the diamonds, combined with existing plate tectonic models of continent migration, showed that diamonds formed at great depths beneath Gondwana when the supercontinent covered the South Pole, between 650–450 million years ago,” notes Dr. Smit.
During diamond formation, the host rocks became buoyant, transporting subducted mantle material along with the diamonds. This material was added to the base of Gondwana’s root, effectively “building” the supercontinent from beneath.
As Gondwana began to break apart around 120 million years ago, forming present-day oceans like the Atlantic, the diamonds — carrying tiny inclusions of the host rock — were thrust to the Earth’s surface through violent volcanic eruptions.
The present-day locations for these volcanic eruptions can be found on the continental fragments of Brazil and Western Africa, which were integral parts of Gondwana. This implies that the diamonds traveled together with various components of the former supercontinent as it disintegrated, essentially “anchored” to its base.
“This complex history of the diamonds shows that they are remarkably well-traveled, both vertically, and horizontally, within the Earth – tracing both the formation of the supercontinent and the latter stages of its evolution,” says Dr. Smit. “The accretion of relatively young material to the roots of the continents thickens and welds together these ancient continental fragments indicating a potential new mode of continent growth.”
Dr. Smit, who conducted the isotope analyses of sulfide inclusions at the Carnegie Institution for Science, is now part of a team at the University of the Witwatersrand working on establishing a new isotope laboratory and methodologies to conduct similar diamond inclusion analyses locally.
“We have installed the necessary equipment in 2022 and are working towards getting the highly specialized skills and equipment together so we can do this type of diamond work in South Africa, where previously it could only be done overseas,” notes Dr. Smit. “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 the journal Nature.
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