Innerer Erdkern möglicherweise älter als gedacht

[karmaka]

Der innere feste Erdkern ist möglicherweise 1,2 Milliarden Jahre älter als gedacht

Forschungsergebnisse von Aleksey Smirnov, einem Professor für Geophysik von der University of Rochester and Yale, und seinen Mitarbeitern legen nahe, dass der feste Erdkern möglicherweise 1,2 Milliarden Jahre älter ist als angenommen und somit vor 2 bis 3,5 Milliarden Jahren entstanden ist.

http://www.mtu.edu/news/stories/2011/november/story51323.html (11.11.11)
http://www.mtu.edu/news/images/2011/image51320-horiz.jpg

autom.Übersetzung: http://translate.google.de/translate?sl=en&tl=de&js=n&prev=_t&hl=de&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.mtu.edu%2Fnews%2Fstories%2F2011%2Fnovember%2Fstory51323.html

http://www.sciencedirect.com/science/article/pii/S0031920111000926  (Mai 2011)

Physics of the Earth and Planetary Interiors; Volume 187, Issues 3-4, August 2011, Pages 225-231
Special Issue: Planetary Magnetism, Dynamo and Dynamics

Abstract

Paleomagnetic data provide one of the few probes available to interrogate early evolution of the core. Here we apply this probe by examining the latitudinal dependence of paleosecular variation (PSV) data derived from high-quality paleomagnetic data collected from Proterozoic and Neoarchean rocks. These data define a Neoarchean geomagnetic field that was more dipolar than that during Proterozoic times, indicating a change in core conditions. The signals observed may reflect a change in forcing of the dynamo and an early onset of inner core growth. We propose a model that links evolution of the core, mantle and crust in three principal phases: (i) Before approximately 3.5 Ga, an entirely liquid core may not have hosted a geodynamo. If heat transport was sufficient across the core–mantle boundary, however, a geodynamo could have been generated. If so, sources in the shallow outer core could have been more important for generating the dynamo relative to deeper convection, resulting in a field that was less dipolar than that generated in later times. (ii) Cooling of the lower mantle between ca. 2 and 3.5 billion years ago was promoted by deep subduction and possibly coincided with inner core growth. The geodynamo during this episode was deeply-seated producing a highly dipolar surface magnetic field. (iii) After ca. 2 billion years ago, continued subduction led to large-scale core–mantle boundary compositional and heat flux heterogeneity. With these changes, shallow core contributions to the geomagnetic field grew in importance, resulting in a less dipolar field. [...] ► The solid inner core may have formed between ca. 2 and 3.5 billion years ago.

(Quelle: http://www.sciencedirect.com/science/article/pii/S0031920111000926  )

 

Martin

[karmaka]

Und er dreht sich ein wenig schneller als die Erde in östlicher Richtung

Die Dynamik des inneren Erdkerns

LINK

Electromagnetically driven westward drift and inner-core superrotation in Earth’s core
P.W. Livermore, R. Hollerbach and A. Jackson

Abstract

[karmaka]

Neue Ideen zur Entstehung des Erdkerns

LINK

Formation of an interconnected network of iron melt at Earth’s lower mantle conditions

Nature Geoscience (2013) , doi:10.1038/ngeo1956

Core formation represents the most significant differentiation event in Earth’s history. Our planet’s present layered structure with a metallic core and an overlying mantle implies that there must be a mechanism to separate iron alloy from silicates in the initially accreted material1, 2. At upper mantle conditions, percolation has been ruled out as an efficient mechanism because of the tendency of molten iron to form isolated pockets at these pressures and temperatures3, 4, 5, 6. Here we present experimental evidence of a liquid iron alloy forming an interconnected melt network within a silicate perovskite matrix under pressure and temperature conditions of the Earth’s lower mantle. Using nanoscale synchrotron X-ray computed tomography, we image a marked transition in the shape of the iron-rich melt in three-dimensional reconstructions of samples prepared at varying pressures and temperatures using a laser-heated diamond-anvil cell. We find that, as the pressure increases from 25 to 64 GPa, the iron distribution changes from isolated pockets to an interconnected network. Our results indicate that percolation could be a viable mechanism of core formation at Earth’s lower mantle conditions.

Schematic diagram showing possible Earth core formation mechanisms

Regions of interest in the Fe-melt/silicate sample prepared under different pressure–temperature conditions.

3D distribution of iron alloy melt in silicate perovskite

[Andyr]

Das erinnert mich im ersten Moment an Melt Pockets. Auch hierfür sind ja u.a. hohe Drücke verantwortlich. Im einen Fall ist es ein kurzzeitdynamischer Impaktdruck im anderen Fall dauerhafte isostatische Drücke. Die Maßstabe sind natürlich auch gänzlich andere. Aber trotzdem scheinen beide Prozesse zu ähnlichen Ergebnissen zu führen.