Diamonds Nearly as Old as Earth- rockhound, geology article

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.

“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.

“To reach a pressure in the mantle, we need a relatively thick continental
crust,” Geisler explained. “That means we already had rocks [on Earth].”

The study will be published in the Aug. 23 issue of the journal Nature.