Why are diamonds belched out from Earth's depths? New study reveals answer

Scientists discover a 25-million-year link 100 miles below Earth's surface, uncovering the mystery behind rare eruptions.
Sade Agard
A large rough white diamond in kimberlite.
A large rough white diamond in kimberlite.


Volcanic eruptions that shoot diamonds high into the sky, scattering them all over the Earth's surface, have long been a captivating mystery for scientists.

Now, a recent study published in Nature may have finally unraveled the mystery behind these extraordinary events. That is, the answer may lie deep underground — more than 100 miles beneath the Earth's surface — involving rare and spectacular forces.

Where at depth do diamonds come from?

The study led by Prof. Tom Gernon from the University of Southampton has shed light on the mysterious processes behind what can be described as rare eruptions. Additionally, the authors provide insights into where diamond-rich deposits are most likely to be found.

“There’s a sweet spot in the interior of continents where diamonds form,” said Prof Tom Gernon, a geologist at the University of Southampton who led the latest study. “The question is why on Earth do they shoot up from the deep after spending potentially billions of years sat there?”

The look further into this, the research team analyzed historical data on continental plates, which are massive slabs of the Earth's crust that move slowly, and kimberlites, the diamond-bearing rocks ejected during these eruptions. 

Their investigation revealed that over the past billion years, most kimberlite eruptions occurred approximately 25 million years after the continental plates tore apart.

Upon closer examination, the scientists observed that the initial kimberlite eruptions that followed the breakup of continental plates were located near the plate edges, while later eruptions took place progressively closer to the middle of the plate.

The process leading to diamond-rich eruptions begins when continental plates are stretched as they start to tear apart, causing the rock to become thinner and disrupting the normal flow of material in the Earth's mantle beneath. 

This disruption is powerful enough to break chunks of rock off the base of the continental plate. Over hundreds of millions of years, the immense pressure on these rocks can cause carbon deposits to transform into diamonds.

As these rock fragments sink into the mantle, they trigger further disruptive flows that spread outwards, stripping layers of rock tens of miles thick from the bottom of the plate above. 

This 'domino effect' creates the conditions necessary for the formation of diamond-bearing kimberlite magma, which rises rapidly and erupts through the crust with tremendous force.

'It’s like rocket fuel'

Kimberlite eruptions differ from regular volcanic eruptions, leaving vertical pipe-like holes in the ground that often become the basis for diamond mines. “It’s like rocket fuel,” expressed Gernon. 

Why are diamonds belched out from Earth's depths? New study reveals answer
One of the deepest quarries in the world. Kimberlite pipe, Mirny Yakutia.

The most recent kimberlite eruption is estimated to have occurred 11,000 years ago in Tanzania's Igwisi Hills, while the majority took place during the Cretaceous period, approximately 146 to 66 million years ago.

Prof. Gernon emphasized the significance of this research for diamond exploration, stating that understanding the events that trigger these eruptions allows scientists to target areas with the highest potential for diamond deposits.

These eruptions are exceptionally rare in Earth's history due to the specific and irregular combination of conditions required to generate them.

He also likened them to a "perfect storm" of events. Their rapid and unexpected nature would have perplexed even the dinosaurs that roamed in some of these areas during these events.

The full study was published in Nature on July 26 and can be found here.

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