Compositional convection and stratification of Earth's core

Fearn, David R.; Loper, David E.

doi:10.1038/289393a0

Cited by 145 publications

(72 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…S) into the liquid outer core as the inner core solidified 11 , as is the case for the present-day geodynamo 6,12 . To assess this hypothesis, the magnetic moment, magnetic Reynolds number and local Rossby number (Extended Data Figure 7) were calculated 13 for a compositionally driven dynamo throughout the period of core solidification (Fig 3c).…”

mentioning

confidence: 91%

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Bryson

Nichols

Herrero‐Albillos

et al. 2015

Nature

151

View full text Add to dashboard Cite

Paleomagnetic measurements of meteorites 1-5 suggest that, shortly after the birth of the solar system, the molten metallic cores of many small planetary bodies convected vigorously and were capable of generating magnetic fields 6 . Convection on these bodies is currently thought to have been thermally driven 7,8 , implying that magnetic activity would have been short-lived 9 . Here we present a time-series paleomagnetic record of the field recorded by the Imilac and Esquel pallasite meteorites, derived from nanomagnetic images 10 of their metallic matrices. The results reveal a history of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shut down of the magnetic field. We demonstrate that magnetic activity driven by progressive solidification of an inner core 11-13 is consistent with our measured magnetic field characteristics and cooling rates 14 . Solidification-driven convection was likely common among small body cores 15 , and, in contrast to thermally driven convection, will have led to a relatively late (hundreds of millions of years after accretion), long-lasting, intense and widespread epoch of magnetic activity among these bodies in the early solar system.The pallasites are slowly cooled (2 -9 K Myr -1 ) 14 stony-iron meteorites 16 , which originated from the mid-to upper-mantle of a ~200-km-radius body 1 . The slow cooling rate of these meteorites allowed for characteristic microstructures to form in their metal matrix 17 , a key feature of which are regions of intergrown nanoscale islands of tetrataenite (ordered FeNi) 18,19 and an ordered Fe 3 Ni matrix 20 , collectively known as cloudy zones (CZ) 21 . During parent body cooling, these tetrataenite islands exsolved and subsequently coarsened over tens of millions of years 22 . The island diameter decreases systematically across the CZ, reflecting a decrease in the local formation age of the islands 20 . Each island adopted one of three orthogonal magnetic easy axes as it formed 18,23 , thus could display any one of six magnetisation directions. Variations in the intensity and direction of an external magnetic field led to measurable differences in the populations of each magnetisation direction 20 . Crucially, the temporal evolution of an external field is recorded by the variations in the relative proportions of these directions across the CZ 10 , which can be quantified using high-resolution nanomagnetic imaging. These images were captured for the Imilac and Esquel pallasites, utilising X-ray magnetic circular dichroism 24,25 at the X-ray photoemission electron microscope (XPEEM) 26 at the BESSY II synchrotron, Berlin, which provides the spatially resolved magnetisation of a sample surface with a resolution down to 40 nm over a 5 µm field-of-view 10 .Four and six non-overlapping, 450-nm-wide regions across the CZ (decreasing age) were extracted from the XPEEM images of Imilac and Esquel meteorites, respectively (Fig. 1). The field recorded by each region was deduced by comparing the experimental XPEEM sig...

show abstract

mentioning

confidence: 91%

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Bryson

Nichols

Herrero‐Albillos

et al. 2015

Nature

151

View full text Add to dashboard Cite

show abstract

“…Fearn and Loper (1981) suggested that light elements could rise through the core and accumulate in a thin layer beneath the coremantle boundary (CMB). Gubbins et al (1982) discussed the possibility of a thermally stratified layer developing over time as the Earth cooled.…”

Section: Introductionmentioning

confidence: 99%

Dynamos with weakly convecting outer layers: implications for core-mantle boundary interaction

Sreenivasan

Gubbins

2008

Geophysical & Astrophysical Fluid Dynamics

View full text Add to dashboard Cite

show abstract

“…Based on the result from many geophysical disciplines, thermal and chemical boundary layers at the base of the mantle are thought to be an origin of mantle plumes (LOPER, 1991). The existence of a stably stratified layer at the top of the core has been discussed with relation to the Earth's thermal history (GUBBINS et al, 1982) or the growth of the inner core (FEARN and LOPER, 1981). The mechanical and/or electromagnetic coupling between the core and mantle was also proposed through geomagnetic studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

Velocities and Chemical Stratification in the Outermost Core

Tanaka

Hamaguchi

1993

J. geomagn. geoelec

View full text Add to dashboard Cite

Travel times of long-period SKS and S2KS phases recorded at the GDSN and WWSSN stations were analyzed to retrieve information about the radial structure of the outer core. We propose a new velocity model for the outermost core named KTH. The velocity at the top of the core is 8.016 km s-1, and the velocity in the outermost 200 km of the core is 0.11 km s-1 faster than that. of HALES and ROBERTS (1971), that in the outer 200400 km of the core is identical within 1% to that of HALES and ROBERTS (1971). We find that the inhomogeneity index rl is slightly larger than unity in the outermost 100,200 km of the core where a preferable value of q just beneath the core-mantle boundary is 1.5 which corresponds to Brunt-Vaisala frequency N of 8.6 x 10-4 s-1. We suggest that the outermost 100200 km of the core is stably stratified. The thickness of the stable stratified layer in the present study is not far from those of 7080 km thickness derived from theoretical considerations. By comparing possible lateral heterogeneity in the outermost core with temperature distribution from a geomagnetic study, we infer that a chemically stratified layer is preferable in the outermost core.

show abstract

Compositional convection and stratification of Earth's core

Cited by 145 publications

References 11 publications

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Dynamos with weakly convecting outer layers: implications for core-mantle boundary interaction

Velocities and Chemical Stratification in the Outermost Core

Contact Info

Product

Resources

About