Scientists probe Earth's core

Apr 28, 2010
Researchers David Eaton and Catrina Alexandrakis from the University of Calgary used measurements of distant earthquakes to learn more about the Earth's core. Credit: Meghan Sired, University of Calgary

We know more about distant galaxies than we do about the interior of our own planet. However, by observing distant earthquakes, researchers at the University of Calgary have revealed new clues about the top of the Earth's core in a paper published in the May edition of the journal Physics of the Earth and Planetary Interiors.

Knowledge of the composition and state in this zone is key to unraveling the source of the Earth's magnetic field and the formation of our planet.

"Some scientists have proposed a region of sediment accumulation at the top of the core, or even distinct liquid layers, but this study shows that the outer core is, in fact, well mixed," says professor Dave Eaton, co-author of the paper. "This inaccessible region is composed of molten iron, nickel and other as-yet unknown lighter elements such as silicon, sulfur, carbon or oxygen."

To help try and determine the materials that make up the Earth's core, which is 2,891 km below the surface, Eaton and co-author Catrina Alexandrakis, University of Calgary PhD student, measured the speed (speed of sound) at the top of Earth's core.

"Observation of distant earthquakes is one of the few tools that scientists have to investigate deep parts of the Earth," says Alexandrakis. "This isn't the first time data has been used, but our research method is the most definitive to date."

The researchers' method is based on 'listening' to earthquakes on the other side of the planet using an approach that is akin to hearing a conversation across a whispering gallery, such as those in the domes of some large cathedrals.

Using a novel digital processing approach, they analyzed faint signals, produced by 44 earthquakes, and were able to measure the sound speed at the top of Earth's core with unprecedented accuracy.

Their results will help to guide research efforts at laboratories where core composition is studied by simulating extreme pressure and temperature conditions that exist in the Earth's core.

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More information: Precise seismic-wave velocity atop Earth's core: No evidence for outer-core stratification by Catherine Alexandrakis and David Eaton is published in the journal Physics of the Earth and Planetary Interiors: dx.doi.org/10.1016/j.pepi.2010.02.011

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omatumr
1 / 5 (2) Apr 28, 2010
Thanks for this publishing this story about the research of David Eaton and Catrina Alexandrakis.

Some believe that Earth may have accreted heterogeneously - beginning with the formation of its core from Fe,Ni-rich material produced by the e-process in the deep interior of a supernova.

Such material might have formed Earth's solid core.

Beyond the Fe,Ni rich material would be S, then Si, and finally O - according to the onion-skin model of a pre-supernova star.

The present study found no evidence of stratification in the outer core, a liquid alloy of Fe and Ni with a 10% fraction of light elements such as O, S, or Si.

With kind regards,
Oliver K. Manuel
out7x
not rated yet Apr 29, 2010
Travel time tomography of Pwaves or Swaves or ???????????????
Sepp
1 / 5 (1) May 01, 2010
In a certain sense we are blinded by what we already know - or rather what we think we know - so any interpretation of the waves' behavior by these scientists must conform to the rigidly set dogma of a molten interior of the earth.

What a pity. It would be so interesting to see something new, something we didn't have a clue of before, but it apparently isn't to be ... yet.
omatumr
1 / 5 (1) May 01, 2010
In a certain sense we are blinded by what we already know - or rather what we think we know - so any interpretation of the waves' behavior by these scientists must conform to the rigidly set dogma of a molten interior of the earth.

What a pity. It would be so interesting to see something new, something we didn't have a clue of before, but it apparently isn't to be ... yet.


Actually there is something new about the giant balls of iron (iron meteorites) that accreted to form Earth's core.

In 1991 Qi-Lu reported that isotopes of molybdenum retained nucleogenetic isotopic anomalies from the reactions that made them, even in massive iron meteorites [Qi-Lu, Doctoral Dissertation, The University of Tokyo, 1991].

This finding, later confirmed by others [ Nature 415 (2002) 881], shows that iron meteorites formed directly from the iron-rich region of SN debris, not by geochemical differentiation of an interstellar mix of elements.

With kind regards,
Oliver K. Manuel