272.05
dollars
Gold price
per ounce on
Sept. 6, 2001
1,895.00
dollars
Gold price
per ounce on
Sept. 6, 2011
Earthly riches may be heaven-sent
Meteorites possibly peppered planet with precious metals
By Devin Powell
A meteorite maelstrom that pummeled
Earth and pocked the moon with craters
billions of years ago may have had a silver lining — and linings made of other
metals, too.
New evidence from old rocks suggests
that many of the precious metals mined
today were delivered to the planet by
stony meteorites called chondrites in a
bombardment that lasted for hundreds
of millions of years.
JULIAN BAUM/TAKE 27 LTD
“Adding a tiny amount of chondritic
material could explain where many present-day metals came from,” says Matthias
Willbold, a geochemist at the University
of Bristol in England, whose team reports
the findings in the Sept. 8 Nature.
Within 50 million years of Earth’s formation, much of its iron sank to the middle to form the core. Gold, platinum and
some other precious metals followed.
Searching for a source that could have
later replenished these metals, Willbold
and colleagues looked for different forms,
known as isotopes, of the metal tungsten
in rocks from the 3.8-billion-year-old
Isua greenstone belt in Greenland. The
belt probably formed before the massive
influx of meteorites that geologists call
the late heavy bombardment.
Compared with the Greenland specimens, newer rocks contain lower ratios
of light tungsten to standard tungsten,
the team found. Chondritic meteorites
don’t have much of the lighter tung-
sten-182 compared with Earth’s mantle,
Meteorites that pummeled Earth
billions of years ago may have depos-
ited the precious metals mined today.
so meteorites mixed into the mantle over
geologic timescales could have diluted
Earth’s younger rocks. The amount of
incoming material needed to explain
the tungsten discrepancy would bring
enough metals to the planet to account
for the quantities of those elements
observed today, says Willbold.
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A DEC
IRVING AWARD
Ian Tebbett
Outstanding Leadership
2011
