Science & Society Features

Diamond Impurities Bonanza for Geologists Studying Earth’s History

July 21, 2011
(accessed 8/19/11)

Diamonds are valuable gemstones that are prized for their beauty, rarity, and mystique throughout the world. But diamonds are also valuable to geologists studying Earth environments in the mantle, about 125 miles below ancient continental cratons, where intense metamorphic temperatures and pressures exist. Volcanic eruptions originating at great depth form kimberlite “pipes,” which incorporate diamond-bearing mantle rock into the magma and deliver them to the surface. The linked article presents a novel way of using impurities in diamonds, called “inclusions,” to study ancient Earth processes. The research was funded by the U.S. National Science Foundation, which is the federal agency that supports original research and education in all scientific fields.

Please answer the following questions.

1. Diamonds are a metamorphosed form of carbon—the element that also is abundant in all living organisms. Simplified explanations suggest that diamonds formed through the metamorphism of coal (the carbon-rich remains of land plants). You’ll learn in Chapter 13 that land plants first appeared in the Silurian Period, and swampy forests suitable for coal formation became abundant about 400 million years ago, in the Devonian Period.
2. Based on your understanding of plate tectonic processes and your reading of the linked article, what is incorrect about the explanation that “diamonds are metamorphosed coal”?
3. The highest quality gemstone diamonds are free of any imperfections or impurities. Geologists prefer diamonds that have inclusions, which are tiny mineral grains incorporated into the diamond. What information is contained in the diamond inclusions that make them so valuable to geologists?
4. A Wilson cycle is:
5. What is the most abundant rock in the mantle?
6. According to the findings of the researchers described in the article, when did the Wilson cycle of plate tectonics first begin on Earth?

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