Oldest Diamond find could shed light on early Earth
Gems found in Western Australia are more than 4 billion years old
Diamonds are indeed forever, or at least nearly as old
as the Earth, a new study shows.
Scientists have unearthed diamonds more than 4 billion
years old and trapped inside crystals of zircon in the Jack Hills region in
Western Australia. Nearly as old as Earth itself and considered the oldest
terrestrial diamonds ever discovered, the gems could give insights into the
early evolution of our planet's crust.
By
Jeanna Brynerfound Aug. 22, 2007 at msnbc.msn.com
A transmission light image of Jack Hills zircons from Australia shows an
angular diamond inclusion.
"Jack Hills is the only place on Earth that can
give us this kind of information about the formation of the Earth," said
study team member Alexander Nemchin, a geochemist at Curtin University of
Technology, Western Australia. "We're dealing with the oldest material on
the planet."
Hot or not?
About 4.5 billion years ago, Earth developed from a cloud of dust around a
proto-sun. During its youth, Earth smashed into a planet-size body and its
surface temperatures likely soared above 10,830 degrees Fahrenheit (6,000
degrees Celsius). When the molten Earth cooled, the liquid lava gelled into
rocks. Details about the rocks and when they began to form, a subject of intense
debate, have been limited by sparse data.
One such debate centers on whether early Earth was
covered by oceans of hot lava or if the planet's surface had cooled enough for
rock formation and was covered instead by oceans of water.
Zircon crystals could hold the answer. These crystals
are tough and relatively resistant to melting. As a result, they retain their
chemical nature and can provide vital clues about past events that occurred in
the Earth's crust and mantle.
Recent studies of zircons have suggested the Earth
might have cooled much more rapidly than previously thought, with the
continental crust and oceans forming as early as 4.4 billion years ago.
The diamond find supports this quick-cooling idea, said
study team member Thorsten Geisler of the Institute of Mineralogy at the
University of Münster in Germany.
Dating diamonds
The scientists, led by Martina Menneken of the Institute of Mineralogy, ran
chemical analyses of the zircons, finding the ancient crystals (and thus the
enclosed diamonds) were more than 4 billion years old. That's nearly a billion
years older than the previous oldest-known terrestrial diamonds and suggests the
diamonds were present in material that crystallized within 300 million years of
the formation of Earth, the scientists say.
After considering different diamond-formation
scenarios, the scientists concluded the jewels most closely resembled those
found in ultra-high pressure conditions. They interpret the findings to indicate
that Earth had a relatively thick continental crust by 4.25 billion years ago.
"I'm quite convinced the Earth must be cooler than
previously thought because otherwise we couldn't have found diamonds,"
Geisler told LiveScience. That's because to form diamonds, heavyweight pressures
are required.
How Are Diamonds Made?
Tuesday May 29, 2007 found at livescience.com
Diamonds are made out of carbon—highly organized carbon, that is. Geologists are still guessing how diamonds formed in the Earth from 1 billion to 3 billion years ago, according to a recent study in the journal Nature, but they think the recipe follows something like this:
- Bury carbon dioxide 100 miles into Earth.
- Heat to about 2,200 degrees Fahrenheit.
- Squeeze under pressure of 725,000 pounds per square inch.
- Quickly rush towards Earth’s surface to cool.
If the process sounds a little difficult, thank a synthetic diamond manufacturer: There are now two ways to make diamonds in the laboratory.
The first synthetic diamonds method is called high pressure, high temperature (HPHT for short). It’s the closest thing to the diamond-producing bowels of the Earth, subjecting graphite (yes, the stuff in a No. 2 pencil, which is made from pure carbon) to intense pressure and heat. Tiny anvils in an HPHT machine squeeze down on the graphite as intense electricity zaps it, producing a gem-quality diamond in just a few days. These diamonds, however, aren’t as pure as natural diamonds because a metallic solution is mixed in with the graphite.
The other diamond-producing method—called chemical vapor deposition—turns its back on intense pressure but cranks out diamonds more flawless than nature can produce. Manufacturers place a piece of diamond into a depressurizing chamber, then zap natural gas with a microwave beam. As the gas is heated to almost 2,000 degrees, carbon atoms “rain” down onto the diamond in the chamber and stick to it, growing a perfect sheet of diamond overnight.
While De Beers isn’t happy with its new competitors, computer manufacturers have something to be excited about: At temperatures that would melt silicon wafers, sheets of synthetic diamond stay rock-hard.
