Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Ironing out the details of the Earth's core

Caltech researchers obtain highest-pressure vibrational spectrum of iron

Identifying the composition of the earth's core is key to understanding how our planet formed and the current behavior of its interior. While it has been known for many years that iron is the main element in the core, many questions have remained about just how iron behaves under the conditions found deep in the earth.

This shows the vibrational spectrum of iron, the most abundant element in Earth's core, at 171 gigapascals. By squeezing iron between two diamond anvils (inset), Caltech researchers reproduced the pressures found in Earth's core. Credit: Caitlin A. Murphy

Now, a team led by mineral-physics researchers at the California Institute of Technology (Caltech) has honed in on those behaviors by conducting extremely high-pressure experiments on the element.

"Pinpointing the properties of iron is the gold standard—or I guess 'iron standard'—for how the core behaves," says Jennifer Jackson, assistant professor of mineral physics at Caltech and coauthor of the study, which appears in the December 20 issue of Geophysical Research Letters. "That is where most discussions about the deep interior of the earth begin. The temperature distribution, the formation of the planet—it all goes back to the core."

To learn more about how iron behaves under the extreme conditions that exist in the earth's core, the team used diamond anvil cells (DAC) to compress tiny samples of the element. The DACs use two small diamonds to squeeze the iron, reproducing the types of pressures felt in the earth's core. These particular samples were pressurized to 171 Gigapascals, which is 1.7 million times the pressure we feel on the surface of the earth.

To complete the experiments, the team took the DACs to the Advanced Photon Source at Argonne National Laboratory in Illinois, where they were able to use powerful X-rays to measure the vibrational density of states of compressed iron. This information allows the researchers to determine how quickly sound waves move through iron and compare the results to seismic observations of the core.

"The vibrational properties that we were able to measure at extraordinarily high pressures are unprecedented," says Jackson. "These pressures exist in the earth's outer core, and are very difficult to reproduce experimentally."

Caitlin Murphy, a graduate student in Jackson's group and first author of the paper, says the group was happy to find that their data set on the vibrational properties of iron evolved smoothly over a very wide pressure range, suggesting that their pressure-dependent analysis was robust, and that iron did not encounter any phase changes over this pressure range. To help achieve these successful measurements at high pressures, the group used some innovative techniques to keep the iron from thinning out in the DACs, such as preparing an insert to stabilize the sample chamber during compression. Additionally, they measured the volume of the compressed iron sample in situ and hydrostatically loaded the iron sample with neon into the sample chamber.

"These techniques allowed us to get the very high statistical quality we wanted in a reasonable amount of time, thus allowing us to obtain accurate vibrational properties of compressed iron, such as its Grüneisen parameter," says Jackson. "The Grüneisen parameter of a material describes how its total energy changes with compression and informs us on how iron may behave in the earth's core. It is an extremely difficult quantity to measure accurately."

The team was also able to get a closer estimate of the melting point of iron from their experiments—which they report to be around 5800 Kelvin at the boundary between the earth's solid inner core and liquid outer core. This information, combined with the other vibrational properties they found, gives the group important clues for estimating the amount of light elements, or impurities, in the core. By comparing the density of iron at the relevant pressure and temperature conditions with seismic observations of the core's density, they found that iron is 5.5 percent more dense than the solid inner core at this boundary.

"With our new data on iron, we can discuss several aspects of the earth's core with more certainty and narrow down the amount of light elements that may be needed to help power the geodynamo—the process responsible for maintaining the earth's magnetic field, which originates in the core," says Jackson.

According to Murphy, the next step is to perform similar experiments alloying iron with nickel and various light elements to determine how the density and, in particular, the vibrational properties of pure iron are affected. In turn, they will be able to evaluate the amount of light elements that produce a closer match to seismic observations of the core.

"There are a few candidate light elements for the core that everyone is always talking about—sulfur, silicon, oxygen, carbon, and hydrogen, for instance," says Murphy. "Silicon and oxygen are a few of the more popular, but they have not been studied in this great of detail yet. So that's where we will begin to expand our study."

The study, "Grüneisen parameter of hcp-Fe to 171 GPa," was funded by the California Institute of Technology, the National Science Foundation, and the U.S. Department of Energy. Bin Chen, a former postdoctoral scholar in Jackson's lab, and Wolfgang Sturhahn, senior technologist at NASA's Jet Propulsion Laboratory and visiting associate at Caltech, were also coauthors on the paper.

Lawren Markle | EurekAlert!
Further information:

More articles from Earth Sciences:

nachricht UCI and NASA document accelerated glacier melting in West Antarctica
26.10.2016 | University of California - Irvine

nachricht Ice shelf vibrations cause unusual waves in Antarctic atmosphere
25.10.2016 | American Geophysical Union

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

'Neighbor maps' reveal the genome's 3-D shape

27.10.2016 | Life Sciences

Gene therapy shows promise for treating Niemann-Pick disease type C1

27.10.2016 | Life Sciences

Solid progress in carbon capture

27.10.2016 | Power and Electrical Engineering

More VideoLinks >>>