Thanks to some gracious access to diamonds by the prestigious mining company De Beers and other firms, geologists are cracking some of the precious stones apart, figuring out just how old they are and gaining clues to Earth's early development.
The results support a theory that just more than 3.3 billion years ago Earth was mostly a water world with little of the land that would one day become continents.
Steven Shirey and David James of the Carnegie Institution of Washington, along with a team of researchers, examined imperfect, cast-off gems donated by large diamond miners. Minerals trapped in the diamonds represent flaws that make the stones worth little or nothing as jewelry, but they can serve as geologic clocks, Shirey explained in a telephone interview with SPACE.com.
The researchers combined this new diamond work with the results of examinations of more than 4,000 diamonds studied during the past two decades, plus new seismic pictures of the deep diamond source region.
Precious clues
Relatively little is known about the early Earth. The continents we know today were once joined in one supercontinent, called Pangaea. Prior to that era, Pangaea had grown from the gathering of small, early continents. At least that's how leading theorists see it.
But there is precious little evidence for anything that happened back then because Earth puts so much energy into digesting its surface and spitting it back out through volcanoes.Diamonds, however, are nearly forever. They survive the chaos of planetary evolution and can even be trapped inside lava. Moreover, some of the mineral grains trapped inside some flawed diamonds are radioactive. They decay over time and produce byproducts.
Shirey and his colleagues studied the ratios of the minerals to the byproducts to learn not only how old the diamonds were but under what conditions they formed. While most diamonds have been brought to the surface relatively recently, they were typically created billions of years ago.
"Every diamond that carries a grain of mineral in it has potentially some information from the source area at the time the diamond crystallized," Shirey said. "We used the diamonds as geologic probes of a portion of the mantle that would be more than 100 kilometers [62 miles] beneath the surface."
Down there, under the Earth's crust, is where continents gain their footing.
The findings
The study, based on diamonds collected in southern Africa, supports a scenario for how Earth looked 3.3 billion years ago.
"Probably it was a time when there wasn't much continent around at all, and early continental nuclei were first being generated," Shirey said.
Most of the Earth at that time was covered by water, he said. Some volcanism was probably occurring on the ocean floor. Other scientists have not been able to determine for sure whether there was life on Earth yet.
Other diamonds examined in the study were dated to a distinctly later period, some 2.9 billion years ago, when Shirey says there appeared to be collision of continental fragments and the closing of intervening ocean basins.
"This could represent a time when the continent was actually stabilized in a form like we see today," he said.
The full results will be published in the Sept. 6 issue of the journal Science.
Economics and science
Shirey said diamonds occur in very small quantities -- parts per billion in rock. Mining companies first test a region to see if its chemistry appears suitable for diamond formation. Then in a larger test they crush several tons of the material to see if a few diamonds exist. Only then might full mining operations begin.
Scientists could not afford to look for their own diamonds, he said.
"They're just being supportive of the academic community to make diamonds available for research," Shirey said of the various mining companies that provided the gems. His team is also working with a couple of small diamond producers who can't financially support such an effort, but which have mines in areas that are important to further study.
He expects to pay for the nearly worthless jewels the smaller companies provide. And then, as with the other diamonds they've examined, Shirey and his colleagues will ruin them completely by cracking them open to get at their geologic clocks.
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