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Powering Earth’s dynamo with magnesium precipitation from the core

O'Rourke, Joseph G. and Stevenson, David J. (2016) Powering Earth’s dynamo with magnesium precipitation from the core. Nature, 529 (7586). pp. 387-389. ISSN 0028-0836. http://resolver.caltech.edu/CaltechAUTHORS:20151123-091123924

[img] Image (JPEG) (Extended Data Figure 1: One example of the evolution of the composition of the precipitate) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 2: Additional results from models of Earth’s core–mantle differentiation) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 3: Posterior probability densities for parameters in the two-stage model of Earth’s core–mantle differentiation) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 1: Parameters with uncertainties used in models of Earth’s differentiation) - Supplemental Material
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Abstract

Earth’s global magnetic field arises from vigorous convection within the liquid outer core. Palaeomagnetic evidence reveals that the geodynamo has operated for at least 3.4 billion years, which places constraints on Earth’s formation and evolution. Available power sources in standard models include compositional convection (driven by the solidifying inner core’s expulsion of light elements), thermal convection (from slow cooling), and perhaps heat from the decay of radioactive isotopes. However, recent first-principles calculations and diamond-anvil cell experiments indicate that the thermal conductivity of iron is two or three times larger than typically assumed in these models. This presents a problem: a large increase in the conductive heat flux along the adiabat (due to the higher conductivity of iron) implies that the inner core is young (less than one billion years old), but thermal convection and radiogenic heating alone may not have been able to sustain the geodynamo during earlier epochs. Here we show that the precipitation of magnesium-bearing minerals from the core could have served as an alternative power source. Equilibration at high temperatures in the aftermath of giant impacts allows a small amount of magnesium (one or two weight per cent) to partition into the core while still producing the observed abundances of siderophile elements in the mantle and avoiding an excess of silicon and oxygen in the core. The transport of magnesium as oxide or silicate from the cooling core to underneath the mantle is an order of magnitude more efficient per unit mass as a source of buoyancy than inner-core growth. We therefore conclude that Earth’s dynamo would survive throughout geologic time (from at least 3.4 billion years ago to the present) even if core radiogenic heating were minimal and core cooling were slow.


Item Type:Article
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http://dx.doi.org/10.1038/nature16495DOIArticle
http://www.nature.com/nature/journal/v529/n7586/full/nature16495.htmlPublisherArticle
http://rdcu.be/fXEXPublisherFree ReadCube access
ORCID:
AuthorORCID
Stevenson, David J.0000-0001-9432-7159
Additional Information:© 2016 Macmillan Publishers Limited. Received 9 January; accepted 26 November 2015. Published online 20 January 2016. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant number DGE-1144469 (J.G.O’R.). Contributions: J.G.O’R. performed the calculations and wrote the manuscript. D.J.S. designed the project, discussed the results, and commented on the manuscript. The authors declare no competing financial interests.
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
Record Number:CaltechAUTHORS:20151123-091123924
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20151123-091123924
Official Citation:Powering Earth’s dynamo with magnesium precipitation from the core Joseph G. O’Rourke & David J. Stevenson Nature 529, 387–389 (21 January 2016) doi:10.1038/nature16495
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62317
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:21 Jan 2016 20:57
Last Modified:21 Jan 2016 23:51

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