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Written by | Stephanie Pappas
Translate | Gong Cong
For most jewelers, the cloudy, pale yellow "fiber diamond" is too ugly. But for scientists, their crystal structure hides very precious secrets that can be used to trace back 1 billion years or more.
Yaakov Weiss, a geoscientist at the Hebrew University of Jerusalem, and colleagues broke up some fiber-bearing diamonds from South Africa and extracted a small amount of liquid trapped in them. These liquids have been around since diamonds were formed, and they have a unique geological record that shows what kind of environment the earth was in long ago. These liquids also contain uranium and thorium, which decay to produce helium4 and gradually leak out of the diamond's lattice. No one knows the exact rate of leakage, but scientists need to use it to determine the age of the diamond and even further uncover the history of the earth's depths.
By modeling the decay process and the rate at which helium-4 could leak, Weiss and colleagues gave a broad chronological range of the diamonds' formation time. Depending on where the diamonds formed, they also ruled out some impossible dating. Combining these two data, the scientists got an upper limit on the rate of helium-4 leakage. They then applied this rate to fiber-containing diamonds under study, which were published in the journal Nature Communications.
The team's findings point out that the liquids belong to 3 distinct periods, each coinciding with the dramatic changes that occur on the surface. The oldest diamonds ranged in age from 750 million to 2.6 billion years, and eventually scientists determined that they formed about 1 billion years ago. The tectonic role of the time was shaping the rugged mountains of today's Africa. Diamonds in the middle stage were formed between 540 million and 300 million years ago, coinciding with the formation of the Nocluf Mountains in Namibia. The youngest diamond was formed between 118 million and 85 million years ago, and then it was brought to the upper crust by a volcanic eruption.
In addition, the oldest diamonds are rich in carbon in their liquids, while the liquids of intermediate and youngest diamonds are rich in silica and salt, respectively. This may also reflect significant geological changes. For example, the liquid in the youngest diamonds may have formed when the oceanic crust was pushed deep into the continental crust.
Suzette Timmerman, an earth scientist at the University of Alberta in Canada who was not involved in the study, says no other rock or mineral in the depths of the earth can reach the surface with so little internal change than diamonds. Therefore, the liquid in diamonds provides a rare opportunity to understand the upper mantle and lithosphere (crust). Timmerman said: "All this in a diamond is basically a time capsule. ”
Next, the researchers plan to study diamonds in other regions to see if there are similar correlations between their formation and surface events, Weiss said: "We need to think further about how we can use these associations to study the evolution of mantles and lithospheres." ”
Source: Global Science