Imperfect diamonds paved road to historic Deep Earth discoveries

Thousands of diamonds, formed hundreds of kilometers deep inside the planet, paved the road to some of the 10-year Deep Carbon Observatory program's most historic accomplishments and discoveries, being celebrated Oct. 24-26 at the US National Academy of Sciences.

Unsightly black, red, green, and brown specks of minerals, and microscopic pockets of fluid and gas encapsulated by diamonds as they form in Deep Earth, record the elemental surroundings and reactions taking place within Earth at a specific depth and time, divulging some of the planet's innermost secrets.

Hydrogen and oxygen, for example, trapped inside diamonds from a layer 410 to 660 kilomet1ers below Earth's surface, reveal the subterranean existence of oceans' worth of H2O - far more in mass than all the water in every ocean in the surface world.

This massive amount of water may have been brought to Deep Earth from the surface by the movement of the great continental and oceanic plates which, as they separate and move, collide with one another and overlap. This subduction of slabs also buries carbon from the surface back into the depths, a process fundamental to Earth's natural carbon balance, and therefore to life.

Knowledge of Deep Earth's water content is critical to understanding the diversity and melting behaviors of materials at the planet's different depths, the creation and flows of hydrocarbons (e.g. petroleum and natural gas) and other materials, as well as the planet's deep subterranean electrical conductivity.

By dating the pristine fragments of material trapped inside other super-deep diamond "inclusions," DCO researchers could put an approximate time stamp on the start of plate tectonics - "one of the planet's greatest innovations," in the words of DCO Executive Director Robert Hazen of the Carnegie Institution for Science. It started roughly 3 billion years ago, when the Earth was a mere 1.5 billion years old.

Diamond research accelerated dramatically thanks to the creation of DCO's global network of researchers and led to some of the program's most intriguing discoveries and achievements.

Diamonds from the deepest depths, often small with poor clarity, are not generally used as gemstones by Tiffany's but are amazingly complex, robust and priceless in research. Inclusions offered DCO scientists samples of minerals that exist only at extreme high subterranean pressure, and suggested three ways in which diamonds form.

While as many as 90% of analyzed diamonds were composed of carbon scientists expected in the mantle, some "relatively young" diamonds (up to a few hundred million years old) appear to include carbon from once-living sources; in other words, they are made of carbon returned to Deep Earth from the surface world.

Diamonds also revealed unambiguous evidence that some hydrocarbons form hundreds of miles down, well beyond the realm of living cells: abiotic energy.

Unravelling the mystery of deep abiotic methane and other energy sources helps explain how deep life in the form of microbes and bacteria is nourished, and fuels the proposition that life first originated and evolved far below (rather than migrating down from) the surface world.

Diamonds also enabled DCO scientists to simulate the extreme conditions of Earth's interior.

DCO's Extreme Physics and Chemistry community scientists used diamond anvil cells - a tool that can squeeze a sample tremendously between the tips of two diamonds, coupled with lasers that heat the compressed crystals - to simulate deep Earth's almost unimaginable extreme temperatures and pressures.

Using a variety of advanced techniques, they analyzed the compressed samples, identified 100 new carbon-bearing crystal structures and documented their intriguing properties and behaviors.

The work provided insights into how carbon atoms in Deep Earth "find one another," aggregate, and assemble to form diamonds and other material.

Related Links
Deep Carbon Observatory
Carbon Worlds - where graphite, diamond, amorphous, fullerenes meet

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How and when was carbon distributed in the Earth?
Matsuyama, Japan (SPX) Oct 14, 2019
It is generally accepted that planetary surfaces were covered with molten silicate, a "magma ocean", during the formation of terrestrial planets. In a deep magma ocean, iron would separate from silicate, sink, and eventually form a metallic core. In this stage, elemental partitioning between a metallic core and a magma ocean would have occurred and siderophile elements would be removed from the magma ocean. Such a chemically differentiated magma ocean formed the present-day Earth's mantle. Previou ... read more