Steve Shirey and Rick Carlson, working with visiting investigators Kalle Westerlund and Stephen Richardson, and colleagues John Gurney and Jeffrey Harris, published a paper in September’s Contributions to Mineralogy and Petrology highlighting their work on dating diamonds from the recently discovered diamond fields in Canada’s Northwest Territories—the oldest precisely dated diamonds on Earth. The diamonds formed 3.5 billion years ago in the Archean Era. The group also reports on evidence suggesting that the diamonds formed during subduction. The research group suggests that these diamonds document one of the oldest known examples of plate tectonics.

The scientists extracted sulfide inclusions from a sample of diamonds, each about 1 carat in weight, excavated from Canada’s Slave Craton’s Panda kimberlite, and determined their age with a dating technique based on the decay of ¹⁸⁷Re to ¹⁸⁷Os. This isotope decays at a predictable rate, making them useful in determining precise ages. To determine the diamonds’ temperature history, Shirey, Carlson and colleagues also looked at how nitrogen—which aggregates with increasing temperatures—was distributed within the lattice structure of the diamonds.

Shirey comments, “Diamonds aren’t just for spectacular jewelry, they are scientific gems too. They act as tiny time capsules. Many diamonds encase tiny mineral grains—what jewelers call impurities, but geoscientists call inclusions—that can tell us how old the diamond is and what geologic processes occurred in the deep Earth billions of years ago.”

For an abstract of the article, see SpringerLink. Click here the full Carnegie Institution press release.