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Oldest diamonds give clues to Earth evolution

28 September 2007

Diamonds more than four billion years old have been found, according to a report in Nature.

The diamonds are nearly as old as the Earth itself and were uncovered from inside crystals of zircon in the Jack Hills region of Western Australia.

The Earth is thought to have formed 4.5 billion years ago. There would have been a huge amount of heat, explosions and violent activity as the Earth's crust and mantle was created.

Any rock or mineral from around this time would need to be very tough to exist unchanged today. 

One such mineral is zircon. Its crystals are extremely tough and relatively resistant to melting, so it is likely to hold clues about how the Earth's crust was made at this time.

Zircon analysis

Martina Menneken and her colleagues studied the minerals inside the zircon crystals and found that some contained small diamonds.

Further analysis dated the zircon, and therefore the diamonds, to over four billion years old. This is nearly a billion years older than the previous oldest diamonds on Earth and only 300 million years away from the time when the Earth formed.

'This work shows that diamonds really are forever,' says Sara Russell, meteorite and cosmochemistry expert at the Natural History Museum.

'Their resilience to chemical and physical processes means that they have an amazing capacity to survive and tell us about very early events.'

The research also suggests that the Earth cooled much more quickly than previously thought with the continental crust and oceans forming as early as 4.4 billion years ago.

Not the oldest diamonds

But the diamonds aren't the oldest known. Sara explains, 'Although the Jack Hills diamonds are the oldest ones known to have formed on Earth, in our collections at the Museum we have meteorites that host diamonds predating even the formation of the Earth.'

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