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Diamonds hold clues about Earth's mysterious evolutionary tale

Ancient, superdeep diamonds from mines in Brazil and Western Africa have recently offered incredible insights into the mysterious evolution of our planet

These diamonds, estimated to have been formed between 650 and 450 million years ago at the base of the supercontinent Gondwana, have unveiled new processes of how Earth’s continents evolved, stabilized, and traversed the globe.

“Superdeep diamonds are extremely rare and we now know that they can tell us a lot about the whole process of continent formation,” said study co-author Dr.  Karen Smit. “We wanted to date these diamonds to try and understand how the earliest continents formed.”

Supercontinent cycle 

Diamonds are remarkable gemstones, not just for their beauty but for their ability to serve as windows into the Earth’s ancient past. These stones, which originated millions to billions of years ago, illuminate the hidden depths and the oldest sectors of the Earth’s mantle. 

The dynamic movement of continents across the Earth’s surface results in the formation and eventual disintegration of “supercontinents,” a phenomenon referred to as the “supercontinent cycle.”

Remarkably, diamonds are among the select few minerals that are strong enough to endure and document these prehistoric cycles of creation and dissolution.

Plate tectonics

Supercontinents play a pivotal role in concentrating deep oceanic plate subduction, the driving force behind plate tectonics, within certain regions. The challenges in directly studying such profound geologic processes, especially from ancient times, are numerous. 

The oceanic crust’s relative youth and the restricted view from the continental crust make old diamonds an invaluable tool, providing a direct glimpse into the deep plate tectonic operations and their correlation with the supercontinent cycle.

The research, led by Dr. Suzette Timmerman of the University of Bern, involved dating tiny silicate and sulphide inclusions within the diamonds. These diamonds formed at staggering depths of 300 to 700km beneath Gondwana. 

Unexpected revelation 

An unexpected revelation surfaced as the team set out to determine how material contributed to the keel of the supercontinent.

“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,” said Dr. Smit. 

In an intricate process, as the host rocks to these diamonds became buoyant, they transported subducted mantle material and the diamonds, thus “growing” the supercontinent from its base. A fascinating chronology of events unfolded, with Gondwana beginning its fragmentation.

“Around 120 million years ago, Gondwana started to break apart to form the present oceans such as the Atlantic,” said Dr. Smit. “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.”

Well-traveled diamonds

The present-day sites of these eruptions are found in Brazil and Western Africa, crucial fragments of Gondwana. Consequently, it’s apparent that these diamonds journeyed alongside various segments of the once-mighty supercontinent, firmly adhered to their base. 

Dr. Smit, who performed the isotope analyses of sulphide inclusions at the Carnegie Institution for Science and is currently at the University of the Witwatersrand, stressed the importance of this research. 

“This complex history of the diamonds shows that they are remarkably well-travelled, both vertically, and horizontally, within the Earth – tracing both the formation of the supercontinent and the latter stages of its evolution,” said Dr. Smit.

Study implications 

“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.”

“We have installed the necessary equipment in 2022 and are working towards getting the highly specialised skills and equipment together so we can do this type of diamond work in South Africa, where previously it could only be done overseas.”

“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 research is published in the journal Nature.

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