How does Earth sustain its magnetic field?
How did the chemical makeup of our planet's core shape its geologic
history and habitability?

Date:
July 6, 2020
Source:
Carnegie Institution for Science
Summary:
Life as we know it could not exist without Earth's magnetic field
and its ability to deflect dangerous ionizing particles. It is
continuously generated by the motion of liquid iron in Earth's outer
core, a phenomenon called the geodynamo. Despite its fundamental
importance, many questions remain unanswered about the geodynamo's
origin. New work examines how the presence of lighter elements in
the predominately iron core could affect the geodynamo's genesis
and sustainability.



FULL STORY ==========================================================================
How did the chemical makeup of our planet's core shape its geologic
history and habitability?

==========================================================================
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles from the solar wind and
more far-flung cosmic rays. It is continuously generated by the motion
of liquid iron in Earth's outer core, a phenomenon called the geodynamo.

Despite its fundamental importance, many questions remain unanswered
about the geodynamo's origin and the energy sources that have sustained
it over the millennia.

New work from an international team of researchers, including current
and former Carnegie scientists Alexander Goncharov, Nicholas Holtgrewe,
Sergey Lobanov, and Irina Chuvashova examines how the presence of lighter elements in the predominately iron core could affect the geodynamo's
genesis and sustainability. Their findings are published by Nature Communications.

Our planet accreted from the disk of dust and gas that surrounded our
Sun in its youth. Eventually, the densest material sank inward in the
forming planet, creating the layers that exist today -- core, mantle, and crust. Although, the core is predominately iron, seismic data indicates
that some lighter elements like oxygen, silicon, sulfur, carbon, and
hydrogen, were dissolved into it during the differentiation process.

Over time, the inner core crystallized and has been continuously cooling
since then. On its own, could heat flowing out of the core and into
the mantle drive the geodynamo? Or does this thermal convection need
an extra boost from the buoyancy of light elements, not just heat,
moving out of a condensing inner core? Understanding the specifics of
the core's chemical composition can help answer this question.

Silicates are predominant in the mantle, and after oxygen and iron,
silicon is the third-most-abundant element in the Earth, so it is a likely option for one of the main lighter elements that could be alloyed with
iron in the core. Led by Wen-Pin Hsieh of Academia Sinica and National
Taiwan University, the researchers used lab-based mimicry of deep Earth conditions to simulate how the presence of silicon would affect the transmission of heat from the planet's iron core out into the mantle.

"The less thermally conductive the core material is, the lower the
threshold needed to generate the geodynamo," Goncharov explained. "With
a low enough threshold, the heat flux out of the core could be
driven entirely by the thermal convection, with no need for the
additional movement of material to make it work." The team found that
a concentration of about 8 weight percent silicon in their simulated
inner core, the geodynamo could have functioned on heat transmission
alone for the planet's entire history.

Looking forward, they want to expand their efforts to understand how the presence of oxygen, sulfur, and carbon in the core would influence this convection process.


========================================================================== Story Source: Materials provided by
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========================================================================== Journal Reference:
1. Wen-Pin Hsieh, Alexander F. Goncharov, Ste'phane Labrosse, Nicholas
Holtgrewe, Sergey S. Lobanov, Irina Chuvashova, Fre'de'ric
Deschamps, Jung-Fu Lin. Low thermal conductivity of iron-silicon
alloys at Earth's core conditions with implications for
the geodynamo. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020-17106-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200706140856.htm

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