BEIJING, April 2 (Xinhuanet) -- Scientists have stuck
a thermometer in the Earth's inner core and found it's really, really hot --
about 9,000 degrees Farhrenheit, just 1,000 degrees cooler than the sun's
The findings will help geologists as they seek to understand how heat is transferred through the planet's
interior, which drives all geologic processes like earthquakes and volcanoes,
and Earth's magnetic field.
Robert van der Hilst of MIT and his colleagues
studied an region under Central America by monitoring earthquake-generated
seismic waves in real time. The speed of the seismic waves indicates the
chemical and physical properties of the material they encounter.
The waves penetrate thousands of miles beneath
Earth's surface, effectively taking the temperature of the boundary between
Earth's core and the surrounding mantle by combining this seismic data with
mineral physics. The team calculated the temperature at this boundary as well as
above and below it.
Specifically, a mineral called perovskite transforms
into so-called post-perovskite at certain temperatures and pressures. The
location of the core-mantle boundary, a place where abrupt temperature and
pressure changes occur, can be identified by locating the exact spot of this
mineral transition. The scientists' calculations put this temperature at about
6,650 degrees. Scientists estimate Earth's inner core to be about 9,000
"What is really the important thing is the amount of heat
that can flow from the core into the mantle, and the amount of heat is related
to the contrast in temperature," van der Hilst said.
Combined with a past study that estimated heat loss
in an area beneath the Pacific Ocean, the research team suggests Earth's total
heat loss at the core-mantle boundary is about 7.5 to 15 terawatts, much higher
than previous estimates. Global energy use by humans is about 13 terawatts.
From their measurements, the scientists
estimate about one-third of the heat that radiates from Earth's surface
into the atmosphere -- estimated to be 42 terawatts -- comes from our planet's
The new temperature measurements will also help
geoscientists refine their understanding our planet's magnetic field, which
protects us from cosmic rays and solar storms. The field fluctuates over time,
for reasons not fully understood, and now and then it even shrinks to zero
before flipping polarity entirely.
"We know the Earth's magnetic field is generated and
maintained in the liquid outer core of the Earth where you basically have rapid
flow of metallic iron," van der Hilst said. Since iron is charged, the swirling
iron mix sets up an electric field that gives rise to Earth's magnetic field.
The turbulent flow is the result of convection, and a
higher rate of heat loss indicates more convection and a faster flow. With
computer simulations, scientists have estimated the amount of energy needed to
maintain the magnetic field. But this study is arguably the first to nail down
concrete estimates, not computer-modeled ones, of these temperatures, van der
"The heat flow that we measure is larger than what is
needed to drive the geo-dynamo, so there is actually more energy down there than
people thought," van der Hilst told LiveScience.
The findings are reported in the March 30 issue of
the journal Science.