Wednesday, 26 September 2012

All of Earth's naturally-occurring gold is
within its core. The gold we mine from
the planet's crust was delivered by
Scientists have shown that the Earth's
surface became enriched with precious
metals by impacting meteorites.
The Earth's crust and mantle has
considerably more gold than expected
from favoured models of planetary
A study from the University of Bristol
looked at some of the oldest rocks on
Earth, demonstrating that gold was
delivered by meteorites long after their
Their results are published in Nature.
While the Earth was forming, iron sank
to the centre of the planet, forming the
Any precious metals in the planetary
mix would have gone with this iron
and concentrated in the core, leaving
the mantle devoid of elements such as
gold, platinum, and osmium.
But this is not what we observe. In
fact, the silicate mantle has up to 1,000
times more gold than anticipated.
Several reasons for this enrichment
were proposed in the past, including
delivery by meteorites, although until
now it has not been possible to prove.
By measuring isotopes in rocks that are
nearly four billion years old from
Greenland, the team has managed to
date the gold delivery, and to relate it
to an event known as the "terminal

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