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The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution (1). Estimates of CMB heat flux (2-5) depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work (6) and fit the seismologically determined core density and inner-core boundary density jump (7,8). We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat fluxbased on mantle convection (1); the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core., First principles calculations of transport properties based on density functional theory (DFT) have been used in the past for a number of materials (see, for example, refs 9, 10). Recently, [...]

The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection (1-3). Mantle convection extracts heat from the core at a rate that has enormous lateral variations (4). Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary (5-7). This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre (7,8) or convection with temperature equal to the solidus but with composition varying from the outer to the inner core (9). The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered (10)., The core responds passively to the non-uniform heat flow imposed by the mantle: it plays a purely passive role in this coupled convective system. Variations in heat flux around the [...]

A three-dimensional kinetic dynamo action for a convection-driven fluid flow class was studied to establish similarities between the geomagnetic field and steady dipole solutions. The influence of the meridian circulation effect on steady and oscillatory solution stability was examined. Magnetic flux concentration, caused by downwelling fluid, was used to determine both sides of the magnetic field morphology.

Melting of Earth's inner core David Gubbins and colleagues present geodynamo simulations showing that variations in heat flow at the core-mantle boundary are transferred to the inner core boundary. They find that the variations can be large enough to cause heat to flow into the inner core and, if this were to occur in the Earth, to cause localized melting. Such melting would release heavy liquid that could form a variable composition layer, providing a simple explanation for seismic velocity anomalies seen immediately above the inner core boundary. Localized melting and freezing could also provide a mechanism to create seismic anomalies in the inner core itself. The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection.sup.1,2,3. Mantle convection extracts heat from the core at a rate that has enormous lateral variations.sup.4. Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary.sup.5,6,7. This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre.sup.7,8 or convection with temperature equal to the solidus but with composition varying from the outer to the inner core.sup.9. The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered.sup.10., Author(s): David Gubbins [sup.1] [sup.2] , Binod Sreenivasan [sup.3] , Jon Mound [sup.1] , Sebastian Rost [sup.1] Author Affiliations: (1) School of Earth and Environment, University of Leeds, Leeds LS2 [...]

The existence of four apparently stationary flux concentrations or lobes at the surface of the liquid core of the earth are revealed by historical geomagnetic measurements which cover 400 years of geological history. Stationary flux concentration is also found in the region from Atlantic to the Indian Ocean. The time average over scale of thousand years is determined by palaeomagnetic data. Geomagnetic field morphology and secular variation have persisted for several million years, as indicated by the data.

Has Earth always had a magnetic field? Yes--or at least for a very long time. There are magnetized rocks of all geological ages, going back some 3 billion years. It [...]

A new model explains the apparent tendency of the virtual geomagnetic pole (VGP) to favor certain longitudinal routes during geomagnetic reversals. The model holds that VGP paths must stay within narrow longitude bands even though the transition field between the Earth's mantle and core is non-dipolar in structure. Moreover, under this model VGP paths indicate core-mantle interaction but not near-dipolar transition fields.

The inner-core of the earth regulates magnetic reversals, and oscillations in the geomagnetic dipole may be good indicators of these magnetic changes. Full reversals arise from large oscillations. The expulsion of magnetic flux beneath the South Atlantic may be responsible for the oscillations. The external section of the inner-core cylinders with expulsion of flux inhibits the dynamo action and renders stability to the inner-core.