Is crystal more precious than diamond
geology : Diamonds found in the oldest crystals in the world
Diamonds have been found in some of the oldest rock strata, up to 4.3 billion years old.
The precious stones are an exciting find for geologists, as they could prove that the earth's crust was thicker than previously thought when it was formed. But future grooms don't have to run to the jeweler to buy the oldest engagement ring in the world. At 70 micrometers, the largest diamond found is barely larger than the diameter of a human hair.
The find shook the world of geologists - including explorers - after it was presented at the Goldschmidt Conference for Geochemistry and Mineralogy (as well as in the Nature (1) issue of August 22nd).
"It was completely unexpected, we hadn't expected it," says Simon Wilde, geochemist at Curtis University of Technology in Bentley, Australia, and co-author of the study. The diamonds could be an indicator that the gigantic plates of the earth's crust moved very early in the earth's history. But to be sure, more extensive studies will be needed.
There aren't many rocks older than four billion years, so we know little about the early days of our 4.5 billion year old planet.
Geologists thought that prolonged asteroid impacts prevented the earth's surface from hardening for the first 500 million years. But as early as the early 1980s, Australian rock researchers found 4.5 billion old zircon crystals in the Jack Hills in western Australia, which were enclosed in much younger rock. This finding suggested a cooler world in which such crystals could form.
Most of the studies that have examined these crystals have focused on the chemical makeup of the zircons themselves. Instead, a team led by Martina Menneken, a geologist at the Westfälische Wilhelmsuniversität in Münster, examined the content of tiny cracks in the zirconium. They found very small diamonds in the crystal, which is between 3.1 and 4.3 billion years old. If the diamonds were the same age as the material around them, the oldest of them would be around a billion years older than any other diamond found so far.
Diamonds are usually created under high pressure. If geologists' calculations are correct about the temperature of the zircons as they were formed, the diamonds may have been formed by the pressure of 100-150 kilometers of rock above them. That would confirm the theory of tectonic earth displacement at this point in time. "The easiest way to get a thicker crust is to hit two continental plates against each other," says Wilde.
Some researchers suggest that the continental plates floated on molten rock 4.4 billion years ago. As a result, they behaved similarly to today, where tectonic movement of the earth plates shifts the continents, creates mountains and sea trenches and causes earthquakes. However, most believe that the earth's crustal movement began only 3-4 billion years ago.
Old or young
The fact that the age of diamonds seems to span such a long period is a mystery, according to the author. It is possible that they all formed 4.3 billion years ago and were later embedded in younger crystals. Or maybe diamonds have been embedded in zircons over and over again over time, in the same place, through a process as yet unknown.
Ian Williams, a geologist at the Australian National University in Canberra, is not convinced of the correct age of the stones. He believes that coal was initially stored in the form of graphite in zirconia of different ages and later turned into diamonds in one fell swoop.
"I think these diamonds will turn out to be not as old as assumed, but I'd be happy if I'm wrong," he says.
One way to test these theories will be to study the nitrogen in the gemstones, Williams says. If the nitrogen atoms are only present individually, this indicates that the diamonds were formed quickly and at relatively low temperatures - if they were e.g. B. would be formed in one fell swoop from graphite deposits in the zirconia. In that case the diamonds would still be young. However, if the nitrogen occurs in pairs or groups, it means that the diamonds were likely created by prolonged pressure. This would confirm the theory that these diamonds were created a very, very long time ago and are therefore the oldest gemstones in the world.
(1) Menneken et al. Nature 448: 917-921 (2007).
This article was first published on 8/22/2007 at [email protected] doi: 10.1038 / news070820-7. Translation: Sonja Hinte. © 2007, Macmillan Publishers Ltd
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