Ancient diamonds unearth new clues about earth's evolution

A remarkable discovery of ancient superdeep diamonds, hailing from mines in Brazil and Western Africa, has illuminated fresh insights into the evolution and movement of Earth's continents.

These diamonds, forged between 650 and 450 million years ago, at the base of the supercontinent Gondwana, have been meticulously analysed by an international team of experts - including from South Africa - shedding light on the enigmatic processes behind the formation and migration of continents during the early stages of complex life on our planet.

Dr Karen Smit, of the Wits School of Geosciences and a key member of this groundbreaking study, hailed the significance of these rare superdeep diamonds.

"Superdeep diamonds are extremely rare, and we now know that they can tell us a lot about the entire process of continent formation," Smit explained.

"We wanted to date these diamonds to try and understand how the earliest continents formed."

Diamonds, which originated millions to billions of years ago, possess the unique ability to illuminate the deepest and most ancient realms of the Earth's mantle. Continents, in their ceaseless journey across the planet's surface, create and obliterate "supercontinents."

These cyclical movements, aptly referred to as the "supercontinent cycle," have largely remained elusive to direct study.

However, diamonds, due to their extraordinary resilience, serve as a record of these ancient cycles of creation and destruction.

Supercontinents have a pivotal role in influencing deep oceanic plate subduction, the driving force behind plate tectonics.

The study of these profound geological processes, especially in the distant past, has posed significant challenges, given the youthfulness of oceanic crust and the limited insights provided by continental crust.

In this regard, ancient diamonds offer a direct window into the intricate workings of Earth's deep plate tectonic engine and its connection to the supercontinent cycle.

The research, spearheaded by Dr Suzette Timmerman of the University of Bern, Switzerland, involved dating the tiny silicate and sulphide inclusions within the diamonds.

This process allowed the team to determine that these diamonds formed at depths ranging from 300 to 700 kilometres beneath the Gondwana supercontinent.

Their goal was to trace how material was added to the keel of this colossal landmass.

Remarkably, during this investigation, the team unveiled a previously unknown geological phenomenon.

The groundbreaking findings have been published in the prestigious scientific journal Nature.

"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," Smit revealed.

The rocks hosting these diamonds became buoyant during the diamond formation process, carrying subducted mantle material along with the diamonds.

This material was subsequently integrated into the base of the Gondwana supercontinent, effectively contributing to its growth from below.

"Approximately 120 million years ago, Gondwana commenced its fragmentation, ultimately giving rise to the present-day oceans, including the Atlantic. Some 90 million years ago, the diamonds, bearing tiny inclusions of the host rock, were brought to the Earth's surface through violent volcanic eruptions," Smit said.

The contemporary locations of these volcanic eruptions are situated on the fragmented continents of Brazil and Western Africa, two significant components of the former Gondwana supercontinent.

This indicates that these remarkable diamonds journeyed alongside different parts of the ancient supercontinent as it disintegrated, effectively "glued" to its base.

"This intricate history of the diamonds underscores their extensive travels, both vertically and horizontally, within the Earth. They provide insights into the formation of the supercontinent and its later stages of evolution. This suggests a potential new mode of continent growth, where relatively young material fuses and consolidates these age-old continental fragments," said Smit.

Smit, now based at the University of the Witwatersrand, is actively involved in establishing a new isotope laboratory and methodologies.

The aim is to enable diamond inclusion analyses to be conducted within South Africa, a significant step towards advancing scientific research in the region.

"We have installed the necessary equipment in 2022 and are working towards acquiring the highly specialised skills and equipment required to conduct this type of diamond research in South Africa, which was previously only feasible overseas," Smit added.

This extraordinary research holds profound implications for understanding the evolution and movement of continents, ultimately revealing the vital role they play in fostering life on Earth.

As Smit eloquently puts 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 how life evolved, ultimately highlighting what makes our planet, Earth, unique among celestial bodies."

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