THE puzzle of the low density of the Earth鈥檚 core may have been partly
explained: it might be full of dissolved hydrogen, says a geochemist.
Geologists believe that about 4.5 billion years ago, the matter in the
forming Earth separated into different layers. Silicate materials became the
molten magma, while most of the iron sank to the central core. Elements that
happily dissolve in iron, such as sulphur and platinum, should also have sunk to
the core. But strangely, the current abundance of these iron-loving elements in
the crust and mantle are higher than expected.
The mystery may have been solved by experiments reported in last week鈥檚
Science (vol 278, p 1781) by Takuo Okuchi of the Tokyo Institute of
Technology. Okuchi heated and compressed iron and silica to re-create conditions
in the Earth鈥檚 core, and exposed them to water. The iron gobbled up the water鈥檚
hydrogen with little ado, while the oxygen joined the silica. Soon 25 per cent
of the atoms in the iron material were trapped hydrogen atoms.
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Okuchi thinks the Earth鈥檚 core was equally hydrogen-hungry as it formed, a
possibility previously ignored by scientists because they thought hydrogen was
too volatile to be trapped in the core. 鈥淲hat鈥檚 interesting is that all the
hydrogen goes into the metal,鈥� says Bernard Wood, a geochemist at the University
of Bristol.
Wood says the hydrogen may have prevented other elements sinking into the
core, explaining the overabundance of iron-loving elements in the mantle. It
would also explain why the core is so light. Studies of seismic waves moving
through the core have hinted that it is 10 per cent less dense than expected.