Diamond Liquid Impurities Provide New Insights into Ancient Earth

May, 2021 - By WMR

To learn more about how old humanity's favorite rocks could be, geologists analyzed tiny pockets of fluid trapped inside diamonds. They discovered three distinct stages of diamond formation in Africa over the last few billion years.

Diamonds are often referred to as "messengers from the deep earth" and scientists research them closely in order to learn more about the otherwise inaccessible depths from which they originate. However, the messages are often difficult to comprehend. Now, a team from Columbia University devised a method for determining the ages of individual fluid-bearing diamonds as well as the chemistry of their parent material. They were able to draw out geologic events dating back over a billion years as a result of the research, which could lead to a breakthrough not just in the study of diamonds, but also in the study of planetary evolution.

The researchers looked at the amounts of uranium and thorium in 10 diamond liquid inclusions, as well as the ratios of these radioactive elements to helium-4, which is emitted as they decay. They also looked at how quickly helium molecules could leak out of the diamond, affecting the ratio. Fortunately, it does not appear that they would be able to flee quickly. The researchers discovered three distinct phases of diamond formation, each with radically different chemical compositions, based on their findings. With inclusions rich in carbonate minerals, the oldest period dates back to 2.6 billion years and 700 million years ago. The second time, which lasted from 550 million to 300 million years ago, has a lot of silica minerals in it. The third phase, which spanned 130 million to 85 million years ago, had a different composition – this time, they were rich in potassium and saline sodium compounds.

Finally, the researchers claim that at the end of this most recent era, massive kimberlite eruptions brought all of these diamonds to the surface. In South Africa, this deposit became the De Beers diamond mine. Surprisingly, one of the diamonds examined by the team showed fluids from both the oldest and youngest ages.