Diamonds and the chemistry of Earth’s mantle

A recent study reveals how the redox state of Earth's mantle, as recorded in diamond inclusions, dramatically influences continental stability. By simulating deep mantle conditions in the lab, researchers demonstrate that oxidized conditions weaken continents while reduced conditions strengthen them, explaining differences in craton behavior between regions like Amazonia and Kaapvaal.

Read the full article at https://www.paperleap.com/blog/articles/a-story-of-diamonds-and-the-hidden-chemistry-of-earth-s-mantle-0cccu2

Episode Transcript

Speaker 1 (00:00):
Welcome to the paper Leap podcast, where a science takes
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(00:21):
Don't forget to subscribe so you never miss an insight.
All the content is also available on paperleap dot com. Okay, ready,
let's start. When most of us think about diamonds, we
picture glittering stones and jewelry cases. But for geologists, diamonds
are much more than symbols of luxury. They're tiny time

(00:44):
capsules from Earth's deep interior. Encased within some diamonds are
microscopic minerals that formed hundreds of kilometers beneath our feet.
These inclusions record secrets about the mantle, the mysterious layer
of rock that makes up most of our planet. A

(01:05):
study published in Science Advances by Ming Di, Gao and
Yu Wang of the guang Jiu Institute of Geochemistry, Chinese
Academy of Sciences, along with Stephen Foley, Macquarie University and
Australian National University and E. Gang Su explores one of
Earth's most fundamental questions, how does carbon traveling deep underground

(01:32):
change the chemistry and even the stability of continents themselves.
To understand this work, we need to talk about something
that might sound abstract, redox state. In simple terms, it's
a measure of how oxidized or reduced a material is,
That is, how many electrons are floating around in its

(01:56):
chemical reactions. Think of it like cooking. Some recipe call
for adding oxygen, like when you caramelize sugar, while others
need things to stay oxygen free, like fermenting beer. In
Earth's mantle, readox chemistry decides whether carbon exists as solid diamond,

(02:16):
as carbon dioxide gas, or locked away in minerals. These differences,
in turn shape vulcanism, the carbon cycle, and even the
stability of ancient continents known as cratons. The surface of
the Earth is constantly recycled into the interior through subduction zones,

(02:37):
where oceanic plates dive under continents along with water and sediments.
These slabs carry carbonates, the same kind of minerals found
in seashells and limestone, down into the mantle. When these
carbonates sink deeper than about two hundred and fifty kilometers,
they encounter a strange environment where metallic iron exists. This

(03:02):
iron can strip oxygen away from the incoming carbonates, changing
their chemistry dramatically. The result is a patchwork mantle with
wildly different redox states, and this is where diamonds come in.
Under certain conditions, carbon crystallizes as diamond, often trapping bits

(03:24):
of surrounding minerals in the process. Those inclusions are like
postcards from the deep mantle, telling scientists about the environment
in which they formed. The team focused on diamonds from
two very different cratons, the Amazonia Craton in Brazil, a vast,
low lying region with thick stable lithosphere, and the Capwall

(03:49):
Craton in South Africa. Fame is for diamond mines, but
geologically more restless, with evidence of past locanism and pieces
of its deep roof missing. Diamonds from Amazonia often carry
mineral inclusions that indicate highly reduced conditions oxygen pore, while

(04:10):
those from Capball suggest a much more oxidized environment. Why
the contrast. To answer this, Goo and colleagues recreated mantle
conditions in the lab using a massive press called the
multi anvil apparatus. They squeezed mixtures of peridotite, which is

(04:30):
a mantle rock, and carbonate type melts, which are slab
derived carbonate liquids, to pressures of up to twenty one
gigapascals equivalent to depths of six hundred and sixty kilometers,
while heating them to over one thousand, seven hundred degrees celsius.
By varying the redox conditions, they could watch what minerals formed.

(04:55):
The results showed that under reduced conditions, carbonate type melts
were consumed and frozen into diamond plus metallic carbon phases.
This matched the inclusion seen in Amazonian diamonds. Instead, under
oxidized conditions, the melts survived, producing carbon rich magmas that

(05:16):
could weaken the lithosphere. This matched the Capball diamonds. In
non plume settings like Amazonia, the subjective carbonates mostly froze
as diamond, strengthening the Creton's keel, the deep root that
makes these ancient continents so stable. That's why Amazonia remains

(05:36):
a flat, intact block today. But in plume influenced regions
like Capfall, hot upwellings tipped the balance toward oxidized conditions.
Carbon rich melts penetrated the lithosphere, weakening it and in
some cases causing pieces of the curtain to peel away,

(05:56):
a process called delamination. This explains the high plateaus, widespread volcanism,
and evidence of lost cretonic root beneath southern Africa. Basically,
diamonds acted as scientific messengers. Their tiny inclusions record the
battle between oxidizing and reducing forces, deep underground forces that

(06:21):
decide whether a Creighton survives for billions of years or
gets eroded away. Beyond diamonds, this story shows how the
deep Earth breathes, recycles, and reshapes itself. The balance of
Readock's reactions in the mantle determines not only the fate
of ancient cratons, but also how carbon moves between Earth's

(06:44):
surface and interior in the long run that affects volcanism,
mountain building, and even the climate. That's it for this
episode of the Paperlely podcast. If you found it thought provoking, fascinating,
or just informative, share it with the fellow science nerd.

(07:04):
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