The deepest and most wanted diamonds on Earth are made up of ancient living organisms, according to a new study.
Ultra-rare “ultra-deep continental diamonds” have isotope levels of carbon that suggest they are formed from organic matter, Australian researchers reveal.
These ultra-deep diamonds, which adorn the crown jewels, form more than 250 miles (400 km) below the Earth’s surface before being released in violent eruptions.
Most naturally occurring diamonds form in the Earth’s mantle at depths of around 100 miles (150 km), under extremely high pressures and temperatures exceeding 2,700 ° F.
Diamonds, which are made entirely of carbon atoms arranged in a dense network, are the hardest materials on Earth.
Diamonds Are Forever: Experts Say Ultra-Deep Continental Diamonds Have Isotope Levels Of Carbon That Suggest They Are Formed From Organic Matter
TYPES OF DIAMOND
Depths between 80 and 125 miles
Found at the bottom of the ocean
– Super deep continental
Over 186 miles (300 km) under the continental crust
“This research not only helps to understand the Earth’s carbon cycle, but also has the potential to reveal more secrets of Earth’s dynamic history by tracking the past locations of mantle plumes and superplumes,” said study author Professor Zheng-Xiang Li at Curtin University.
“This can be achieved by mapping the distribution of continental and oceanic diamonds. ”
There are three main types of natural diamonds: “lithospheric”, “oceanic” and ultra-rare “ultra-deep continental” diamonds.
The lithospheric, formed at depths between about 80 and 125 miles (130-200 km) is the most common, accounting for 99 percent of all diamonds mined.
Oceanic ones, on the other hand, are found at the bottom of the ocean, while ultra-deep continental diamonds form more than 300 km below the continental crust.
The continental crust is the outermost layer of what’s called the lithosphere, the outermost rocky shell on Earth.
Earth’s cross section shows the continental crust – the outermost layer of the lithosphere (the outermost rocky shell on Earth)
All three types of diamonds are formed at different levels of the mantle with a varying mixture of organic and inorganic carbon, which can be determined by changes in an isotopic signature of carbon called δ13C (delta carbon thirteen).
Diamonds formed from organic carbon would suggest that they originate from a living organism, as organic carbon compounds are produced in living things.
Previous research has already suggested that δ13C levels in oceanic diamonds suggest an organic origin.
Ultra-deep continental diamonds contain a “surprising” amount of δ13C, similar to oceanic diamonds – and therefore also suggest an organic origin, researchers say.
One of the main differences between oceanic and ultra-deep continental diamonds is that the latter have widely varying levels of δ13C.
The diamonds of the crown jewels
The famous Hope Diamond, can also be “super deep”
The giant gem-cut diamond that now adorns the Crown Jewels formed 400 miles below the Earth’s surface, three times deeper than other gemstones.
Analysis of similar diamonds by the Gemological Institute of America revealed that the Cullinan was a “super deep” diamond and one of the rarest objects on Earth.
The largest gem-quality rough diamond ever found, weighing 3,106.75 carats, the Cullinan was unearthed from a mine in South Africa in January 1905.
In 1907, the diamond was purchased by the government of the Transvaal Colony, who gave it to King Edward VII as a gift.
The king had the rough stone cut by Joseph Asscher & Company of Amsterdam – forming nine major stones (Cullinan I-IX) as well as 96 minor shining stones.
The two largest stones – Cullinan I and II – now form the centerpieces of the Crown Jewels and are found in the Sovereign’s Scepter with Cross and the Imperial State Crown.
Although they originally remained in Amsterdam, the other seven major stones were also acquired or donated over time to the British Royal Family.
The recent study also concluded that the famous Hope Diamond – currently in the collections of the Smithsonian Museum in the United States – may also be “super deep”.
The study’s authors believe this is because very deep nuclei envelop themselves in inorganic crusts in the lithosphere, before being ejected during eruptions.
Ultra-deep oceanic and continental diamonds form in the mantle transition zone – 400-600 km deep – using subducted organic carbon, and then are carried into the lithosphere by mantle plumes.
“Bringing new meaning to the old adage of trash trash, this research found that the Earth’s engine actually turns organic carbon into diamonds several hundred kilometers below the surface,” the study author said. , Dr Luc Doucet of Curtin University.
The diagram in the article explains the origin of types of diamonds. (A) Super deep oceanic and continental diamonds (core only) form in the mantle transition zone using subducted organic carbon, then are brought to lithospheric levels by mantle plumes
“The bloating of rocks in the Earth’s deeper mantle, called mantle plumes, then bring the diamonds back to the earth’s surface via volcanic eruptions for humans to enjoy as sought-after gems.
“As recycling becomes a modern necessity for our sustainable survival, we were particularly surprised to learn from this research that Mother Nature has been showing us how to recycle in style for billions of years. ”
The research provides a model that explains the formation and location of the three main types of diamonds, according to the team.
Hot air balloon rocks in the Earth’s deeper mantle, called mantle plumes, carry diamonds to the Earth’s surface via volcanic eruptions (stock image)
“This is the first time that the three main types of diamonds have been linked to mantle plumes, hot rocks swollen by plate tectonics and the cycle of supercontinents from deep within the Earth,” said Professor Li , author of the study.
It remains a mystery as to why the diamonds formed in the mantle transition zone are formed only from recycled organic carbon.
“It might have something to do with the physico-chemical environment there,” added Professor Li.
“It is not uncommon for a new scientific discovery to raise more questions that require further investigation.”
The study was published in Scientific reports.
HOW ARE DIAMONDS FORMED?
Natural diamonds formed more than 3 billion years ago deep in the earth’s crust under conditions of intense heat and pressure.
These conditions cause carbon atoms to crystallize, forming diamonds.
The diamonds are found at a depth of approximately 150 to 200 kilometers (93 to 124 miles).
Temperatures here average 900 to 1,300 degrees Celsius, with pressures of 45 to 60 kilobars (roughly 50,000 times the atmospheric pressure at the Earth’s surface).
Under these conditions, molten lamproite and kimberlite (known as magma) also form in the Earth’s upper mantle, and they expand at a rapid rate.
This expansion shatters the magma, forcing it to rise to the Earth’s surface and dragging diamondiferous rocks with it.
The magma erupts forming a “pipe” on the surface, and as it cools, the magma hardens to form kimberlite, settling in vertical structures called kimberlite pipes.
These pipes are the most important sources of diamonds, but only about 1 in 200 kimberlite pipes contain gem-quality diamonds.
The name ‘Kimberlite’ comes from the South African town of Kimberley, where the first diamonds were found in this type of rock.
Source: Cape Diamond Museum