Lighter filling in Earth’s core

Jun 23, 2005

New experiments conducted by a team led by the Carnegie Institution’s Dr. Jung-Fu Lin suggest that the core of the Earth may contain more light elements than previously thought. The research is published in the June 24, 2005, issue of Science.

“The composition of Earth’s core has been the subject of scientific debate for years,” commented Lin. “The prevailing consensus is that the outer core is a molten cauldron mostly of iron with some light elements and the inner core is made of solid iron with a little bit of light elements. We can’t sample the core directly, so we’ve made these estimates by reading seismic waves as they travel through the interior and through experimentation and theory,” he continued.

As depth increases inside the Earth, so does the pressure and heat. The pressure in the core varies from 1.4 million times the pressure at sea level at the outer edge of the core, to 3.6 million times that pressure at its center. Current models suggest that center conditions are also a scorching 8,000 to 10,000 degrees Fahrenheit (5000 to 6000 K). Materials in this environment become so compressed, dense, and hot that the atoms behave very differently from those under normal conditions. Until now, scientists have deduced the nature of core materials by measuring seismic waves as they pass through the interior and applying a law known as Birch’s law, which predicts that sound velocities travel slower through less-dense material and faster through denser materials. The scientists discovered through their experiments on iron, however, that temperature had a significant effect, with a resulting impact on the velocity/density relationship. “We found that when temperature is added to the experiment, the velocities of the compression waves (the waves that force atoms closer for a moment) and shear waves (when the atoms rub against each other) actually decreased with increasing temperature even though the pressure was moderately high,” stated co-author of the study Wolfgang Sturhahn.

The researchers compared their results with seismic-wave measurements of the Earth’s interior and determined that there are more light elements contained in the iron there than previously inferred from linear extrapolation at room temperature.

“The law is a first approximation,” stated Lin. “It assumes that we only needed to consider the density effect in the interior. Our study demonstrates that we need to deal with the pressure and temperature effects.”

Using a diamond-anvil pressure cell, the scientists subjected iron to pressures up to about 720,000 times the atmospheric pressure at sea level, and with laser heating they increased temperatures up to 2,600° F. They witnessed the changes to the iron atoms with the intense X-rays of the nation's premier third-generation synchrotron source, the Advanced Photon Source at Argonne National Laboratory near Chicago. They measured the sound velocity through the compressed, hot iron with a sophisticated technique known as nuclear resonant inelastic X-ray scattering. “The development of this new technique was crucial for our studies, which had to advance far beyond the more common structure investigations to provide us with these unique insights into the planetary interior,” commented Sturhahn, who developed the technique and is leading the High Resolution X-ray Scattering group at the Advanced Photon Source.

“For the past 50 years, Birch’s law has helped geophysicists to understand dense materials under the extreme conditions in Earth’s interior. Our results show how new technology can bring added understanding of the interior,” reflected co-author of the study Ho-kwang (Dave) Mao, the director of the High-Pressure Collaborative Access Team at the Advanced Photon Source.

Source: The Carnegie Institution of Washington

Explore further: To conduct, or to insulate? That is the question

Related Stories

Earth's core reveals an inner weakness

Jan 27, 2014

(Phys.org) —The word "core" conjures up an image of something strong. However, new experiments show that the iron found in the Earth's core is relatively weak. This finding is based on x-ray spectroscopy ...

Earth's iron core is surprisingly weak, researchers say

May 17, 2013

The massive ball of iron sitting at the center of Earth is not quite as "rock-solid" as has been thought, say two Stanford mineral physicists. By conducting experiments that simulate the immense pressures deep in the planet's ...

Going to Earth's core for climate insights

Mar 10, 2011

(PhysOrg.com) -- The latest evidence of the dominant role humans play in changing Earth's climate comes not from observations of Earth's ocean, atmosphere or land surface, but from deep within its molten core.

Recommended for you

To conduct, or to insulate? That is the question

17 minutes ago

A new study has discovered mysterious behaviour of a material that acts like an insulator in certain measurements, but simultaneously acts like a conductor in others. In an insulator, electrons are largely stuck in one place, ...

Soundproofing with quantum physics

18 minutes ago

Sebastian Huber and his colleagues show that the road from abstract theory to practical applications needn't always be very long. Their mechanical implementation of a quantum mechanical phenomenon could soon ...

Extreme lab at European X-ray laser XFEL is a go

1 hour ago

The Helmholtz Senate has given the green light for the Association's involvement in the Helmholtz International Beamline (HIB), a new kind of experimentation station at the X-ray laser European XFEL in Hamburg, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.