Potassium-40 heats up Earth’s core
could be a significant source of heat in the Earth's core.
V Rama Murthy from the University of Minnesota and
colleagues have shown that potassium-40 can exist in the
core of the Earth and provide heat via its radioactive
decay. The result could have important implications for
theories of thermal evolution of planetary cores and the
origin of geomagnetic fields.
Potassium-40, which has a radioactive half-life of about
1.2 billion years, could be an important source of heat
in the Earth's core but this has never been unambiguously
confirmed in an experiment. Murthy and colleagues used an
iron and iron- sulphur mixture to represent the Earth's
core and potassium silicate glass to represent the shell.
They measured the partition coefficient - the
concentration of potassium-40 in the sulphur mix divided
by its concentration in the silicate - at temperatures
and pressures approaching those found deep in the Earth's
The researchers found that the logarithm of the partition
coefficient is inversely proportional to temperature. The
results suggest that potassium-40 can move from the
silicate 'shell' to the iron-sulphur 'core' and that it
would be possible for a high enough concentration of
potassium-40 to build up in the core.
The team calculated a core potassium-40 content of
between 60 and 130 ppm, which produces between 0.4 and 0.8
TW of heat. Estimates of the core-mantle boundary heat
flux are between 8 and 10 TW, so the heat produced by
potassium-40 could significantly contribute to the heat
flux at the boundary. Recent studies have shown that the
present level of heat flux would have been insufficient
to sustain the Earth's magnetic field for the past 3.5
billion years. This 'extra' radioactive heat could thus
have allowed the field to exist.
"We now plan to expand these measurements to much
higher pressures and temperatures," Murthy told
PhysicsWeb. "We shall also extend the experiments to
the other major radioactive heat sources in the Earth,
uranium and thorium."
Zdroj: PhysicsWeb, Belle Dumé
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